Radio Boulevard
Western Historic Radio Museum


Vintage Longwave Receivers - Part 3

Profiling the COLLINS R-389/URR

 Profiling the HAMMARLUND SP-600VLF-31

Profiling the RACAL RA-17C-12 with RA-237-B MW-LF-VLF Converter

Rycom R1307A/GR and Using Selective Level Meters as LW Receivers

Other Receivers with some MW or LF Coverage

Regenerative Receivers versus Superheterodyne Receivers on LW

The Ultimate LW Receiver?





U.S. Army Signal Corps

Collins Radio Company



MW, LF, VLF  Double Conversion Superheterodyne

15kc to 1500kc

SN: 268  from 1951 Contract (1953 build date)


1953 R-389 SN: 268 installed in CY-979A Mobile Table Cabinet

Basic Description - Electronics - Built along some of the same lines as the famous R-390 receiver, the Collins R-389 is essentially the LF companion to the R-390 receiver, covering 15kc to 500kc in one tuning range and 500kc to 1500kc in the second tuning range. The R-389 uses very complex methods, both electronic and mechanical, to achieve its complete MW, LF and VLF coverage while still utilizing a 455kc IF. The receiver uses 36 tubes within five modules that interconnect and are mounted within the main frame. The 15kc to 500kc tuning range utilizes five permeability-tuned RF bands. The 500kc to 1500kc tuning range utilizes two permeability-tuned RF bands. The band switching is motor-driven and occurs seamlessly as the receiver is tuned from the lowest to the highest frequency within the two tuning ranges.

Two RF amplifiers are used and the first conversion mixes the incoming RF signal frequency with the VFO (470kc to 1955kc output f) plus the 10.455mc Crystal Oscillator (8.5mc to 9.985mc resulting f) to achieve a 10mc IF. The second conversion mixes the 10mc IF with the same 10.455mc Crystal Oscillator to achieve the 455kc IF. This double conversion scheme was to allow complete coverage from 15kc to 1500kc with no gaps in the frequency coverage. Additionally, since the two mixer stages are 180 degrees out of phase, any drift within the conversion mixers is cancelled leaving only the VFO drift. This is similar to how the "drift-cancelling" Wadley Loop operates.

From the second mixer circuit on, the R-389 utilizes the same modules that are found in the R-390. That would be the six-stage IF module, the two channel audio and electronic voltage regulator circuit module and the power supply module. Although the 70H-1 PTO (VFO) looks exactly like the one in the R-390, it's very different inside and tunes from 470kc to 1955kc.

Mechanical Details - The manual tuning of the receiver RF front end uses clutch-coupled gears to rotate the main RF tuning shaft that has worm gears that perpendicularly engage and rotate the gear-driven front and rear line shafts that have worm gears that in turn engage gear-driven vertical screw-shafts (cut with forward and reverse threads) that raise and lower the various slug racks. When this gear-driven system is correctly adjusted and lubricated sparingly with light-weight oil it will be easy to manipulate and have the feel of a good condition R-390A gearbox. Since the two tuning ranges cover so much spectrum a clutch-coupled, motor-drive tuning system is provided. A separate motor-drive band switching system is also provided to select the proper band (one of seven) to allow seamless bandswitching as the receiver is tuned throughout it ranges.

The Veeder-Root counter is somewhat different than that used in the R-390 and provides two sets of digits, one for 15kc to 500kc (lower set) and the other for 500kc to 1500kc (upper set.) The resolution of the digits (tuned f) is to the tenth of a kilocycle (which are the red background digit wheels.) Neither a calibration oscillator or an antenna trimmer are provided (or needed.)

Most of the controls are the same as those found on the R-390. The BFO controls, the Noise Limiter, the Local Gain, Line Gain, Line meter range switch, RF Gain, AGC switch, Break-in switch, Audio Response switch and Function switch. The controls that are unique to the R-389 are Motor Drive, IF Bandwidth (five ranges instead of six,) RF bandwidth KC indicator and the single tuning knob. The two meters perform the same functions as the R-390 meters, that is, Carrier Level and Line Level.

More Details - Physically, the R-389 is the same dimensions as the R-390 and will fit into the CY-917 or CY-979 table cabinets. If installed into a table cabinet, the top and bottom covers should be removed. The receiver weighs 82 pounds but, for easier moving (e.g., up or down stairs,) the power supply and AF module can easily be removed and then the receiver weighs around 65 pounds.

Two antenna connectors are available. Balanced input for 125 ohms input impedance from dipoles or other balanced antennae. Balanced is connected to the primary winding of each antenna coil. Unbalanced input is for random length wire antennae. This input is capacitively-coupled through a .01uf capacitor to the RF amplifier coils. The Unbalanced input impedance is not specified but is probably fairly high assuming that end-fed wires were probably the design target Z. The Balanced input utilizes a "Twin-ax" two-pin coaxial connector and the Unbalanced input utilizes a "C-type" coaxial connector. As mentioned, no antenna trimmer is provided so the antenna impedance should be somewhat matched to the particular antenna input used.

Both audio outputs, Local Audio and Line Audio, are 600 Z ohm outputs and can provide about 500mW on Local and about 10mW on Line. The phone jack doesn't disconnect the audio output (LOCAL) from its respective load. There is a series resistor and a load resistor to the PHONES jack to keep the audio level (5mW) from over-driving the headset if the proper 600 Z phones are used.   >>>

photo right
: Top of the R-389 showing the RF module and IF module mounted in the receiver. The RF module has the slug racks located under the cover. The two tubes showing thru the opening are the two RF amplifiers. The Crystal Oscillator and first mixer is the to the left and the second mixer is to the right. The IF module is to the left side of the main frame.

>>>  The AC power connector is a four-pin military connector that is keyed and held in place with a central screw that has a fold-down, wing-type handle. There are at least two different types that fit,...sort of. The original (CX-1358/U cable + connector PN) connector has a small round cylinder-shaped housing with a cable exit tube on the side. This type will fit in almost any orientation and can be used if the receiver is installed into a table cabinet. There is also a large square housing with the triangular top type that will only fit in one orientation that won't interfere with the terminal strip or the fuse housing. With the larger connector installed the receiver must have spacers to elevate the bottom enough for the connector body (if the receiver is setting on a table) to clear the table. Also, with this larger connector, the receiver won't fit into the table cabinets.

Unlike most other LF and VLF receivers, the R-389 doesn't have any fixed-circuit audio restrictions within the audio module other than the switch-selected Broad-Medium-Narrow. Selecting Broad results in a fairly wide audio bandwidth. Medium is shaped for voice with noisy conditions and Narrow is a bandpass filter at 800hz for CW. The IF bandwidth can be restricted down to 100hz. Both 100hz and 1000hz IF bandwidths use a crystal filter that's onboard the IF module. The 2kc, 4kc and 8kc IF bandwidths are determined by the IF transformers and Q-resistor set-up. For static bursts and other types of atmospheric noise, the dual positive-negative noise limiter is available. When tuning in the AM BC range, the receiver's bandwidth can be increased to 8kc and BROAD and, with no other specific audio restrictions, the resulting audio isn't too bad. However, the audio is more-or-less communications-grade audio so don't expect high fidelity because it isn't. Most listening on LW will usually be using a headset. Most listening on the AM-BC band will be on loudspeaker.

The R-389 is a "top notch" MW, LF and VLF receiver but using it today can result in user frustration due the very high noise levels that plague LF enthusiasts in many locations. The R-389 does cope with significant noise levels very well. It can do a good job with a wire antenna (probably what it was designed for anyway) especially if the user is located in a RFI-quiet area. Using a loop antenna may help in extremely noisy areas. Of course, like any LW receiver, best results will be experienced when listening "at night" during the "LW Season" (Oct thru Mar.)

photo right
: Bottom of the R-389 showing the Power Supply module on top, the VFO in the center and the Audio and Electronic Voltage Regulator module on the bottom. Motor drive system is directly behind the front panel. The long rectifier (green with fins) is part of the motor-drive tuning power supply. The long bent metal arm directly behind the tuning knob is the motor-drive clutch actuation arm that is cam-driven from the MOTOR TUNE control. The three coaxial cables behind the VFO are from the Antenna Relay box and are routed to the RF Module.

R-389 Restoration Log (Started March 11, 2018)

This probably isn't really a "restoration" but more of a full and complete "servicing" of the R-389. Includes the removal of any "non-military" modifications in order to return the circuit to the original design. Before starting it's worth noting that the receiver does function - not to spec, but it does receive some signals. This indicates that most circuits are working but probably not aligned where needed. The R-389 is a very mechanical type of receiver and this servicing will probably include not only electronic alignments but also mechanical alignments.

The R-389 Restoration Log has been expanded upon and that enlarged version which contains more information on the VFO end point error adjustments and other details can be found in the "R-389 Section" of "Rebuilding the R-390A Receivers - Part 4"

March 11, 2018 - Disassembled receiver by pulling all modules. Power Supply, Audio-Regulator and IF module are easy. RF module requires dropping front panel. Like the R-390A, the gearbox is integral to the RF module. Only the frequency that the receiver (RF module) is tuned to has to be remembered when doing the reinstallation because the VFO (PTO) remains in the main frame.

March 12, 2018
- Finished dismounting the RF module. Inspection of the line shaft gears showed that some type of black grease was used. It's probably Molybdenum-grease. Excessive amounts of "multi-purpose" grease were used in the gearbox. Like the R-390A gearbox, the R-389 gearbox really doesn't need any grease and copious amounts of grease will just trap dirt and then "harden" over time. The manual states that "no lubrication is better than too much lubrication." A light coat of 10W machine oil is all that's necessary. After all, you wouldn't grease a clock's gear work,...right?

March 13, 2018
- Started removal of the excessive grease. I used WD-40 as a solvent to remove and clean the areas on and around the line shafts of the moly-grease used. This required several "cleanings" to remove all residue. Started removing the excessive multi-purpose grease in the gearbox. Anything that rotated was "greased."

March 14, 2018
- Grease, grease and more grease. Some of the grease in the gearbox is as hard as candle-wax. I'm having to scrape it off in some places. I'm using WD-40 applied with a small paint brush but this doesn't hardly touch the hardened grease. I switched over to a small wire brush and WD-40 which removes the hard grease much better.

March 15, 2018
- Used WD-40 to "flush" the gearbox and that got it very clean with all of the hard grease gone. Cleaned all of the threaded rods that comprise the slug rack lifters. The manual Frequency Change still seemed "heavy." I readjusted the motor-drive clutch and discovered it was adjusted to "full engagement." This had the motor-drive clutch turning with the manual tuning. Once the clutch was adjusted to "slip" when manual tuning, the "heavy" tuning was gone and the gearbox "feel" was very much like a clean R-390A gearbox. Also, the slip-clutch in the tuning knob had been adjusted to "full engagement" because of the heavy tuning. The slip-clutch was adjusted to be engaged with manual tuning but to "slip" if any binding or other drag occurred in the entire tuning mechanism. The problem was caused by all of the grease creating so much drag in the gearwork, the motor-drive clutch had to be in full-engagement to get the motor to turn the gears. The slip-clutch in the knob needed to be in full-engagement to turn both the drive clutch and all of the grease.

photo above: Under the RF module after cleaning off all of the grease. Note the two line shafts that drive the gears that turn the threaded shafts that raise and lower the nine slug racks. The motor-drive bandswitch is in the center of the chassis with the gear drive at the very rear of the module. The motor for the motor-drive tuning is in the lower right of the photo. Note the date on the motor - Sep 10 53.

March 17, 2018 - Checked Antenna Relay Box connectors because when operating the receiver, Balanced Antenna didn't seem to work. Found connector J110 center pin damaged on Antenna Relay box. Also, found mating connector, P110 also had center pin bent.

March 18, 2018 - Dismounted Antenna Relay Box and removed bottom plate. I could see that the Balanced Input wiring had been changed from original. The mod has the Bal. Ant. connector wired to go to the output BNC connectors IF the receiver is turned off. When the receiver is turned on, then the Bal. Ant. input is connected to chassis ground. The reason for this mod seems to be prevention of using the Bal. Ant. input. Check April 4th for correction.

March 19, 2018 - Mod to B+ fuse and HV winding CT found. This mod removed the wires from the B+ fuse holder and soldered them together to eliminate the fuse in that circuit. Then the power transformer CT (pin  6) was disconnected from chassis ground in the power supply module and a wire routed from the CT to pin 15 (unused in ps) of J-118. This pin 15 P-118 connection was originally to the DC 20A fuse but was now routed to the B+ fuse holder and then to chassis-ground (on the Local Audio ground terminal.) This mod may have been installed because of the power supply module conversion to solid state rectifiers. It's likely that the "instant on" HV to the electronic regulator circuit tended to blow the 3/8 Amp B+ fuse. With the mod, fuse blowing would be at the power transformer HV winding current draw rather than at the output of the HV rectifiers to the input to the voltage regulator circuit. The mod also changed the fuse to 3/4 Amp.

March 20 - April 3, 2018 - I had to set aside the R-389 project temporarily. A Collins 32V-3 was acquired that needed testing, servicing and clean-up. I'll get back to the R-389 when the V-3 is completed (a few days, hopefully.)

April 4, 2018 - Well, two weeks (two other projects in addition to the V-3) and back to the R-389. De-mod'd the Power Supply by removing wire CT to pin 15 J-118. Reinstalled the correct bare 14 gauge, "tinned-copper" (TC) wire from chassis to both CT pins on power transformer as original. This completed the Power Supply.

Correction - Checked the Antenna Relay Box again and found that it is correct and original. The relay contacts are actually for grounding the antenna inputs when Break-In is actuated.

photo above: The gearbox after cleaning out all of the dried grease. The tuning knob has a built-in slip-clutch that's adjusted by the four recessed screws in the flutes of the knob (two screws are visible in the photo.) Behind the knob is the motor-drive clutch that is engaged when the motor drive switch is turned. This pushes down the lever which pivots against the adjustable standoff to the right and presses the clutch in which then drives the gears for motor tuning. Manual tuning is accomplished with the tuning knob and runs the gear train if the motor drive clutch is disengaged (that is, receiver not in "motor drive.") The tuning knob does "spin" while motor drive tuning.

April 5, 2018 - The B+ fuse mod had actually broken the side terminal off of the DC 20A fuse holder. I had to remove the TC (tinned-copper) wire and the large gauge stranded wire from the to rear terminal in order to remove the broken fuse holder. I located a duplicate of original, good condition, original fuse holder to install.

April 6, 2018 - Removed all wires from non-original connections. Cleaned, straightened and re-tinned all lead ends. Installed DC 20A fuse holder and connected and soldered original wires. Re-wired B+ fuse to now have the original connection to the HV rectifier output. Cleaned all "mod writing" off of the back panel using WD-40 and "Goof-Off." This completed mod removal on the Main Frame.

April 8, 2018 - Performed the check on the mechanical alignment for the RF module. This check involves setting the lower frequency readout to specific frequencies and then checking the height that specific slug racks have been raised. All checks are verifying the each of the nine slug racks are at their maximum lifted height and also at specified heights from the top of the RF coil shields at the specified frequency readout. There are silk-screened frequencies and lines that measure the specified height on the back of the rear panel of the RF module. The test starts at 14.8kc and goes through eight other settings ending with 565.0kc. Though the written procedure is in the manual, it's easier to just use the silk-screened information on the back of the RF module. All nine slug racks were at the proper height at the specified frequency. This check only assures that the slug racks are traveling correctly. The electronic alignment will assure that the slugs themselves are at the correct position for accurate tracking.
April 10 - 14, 2018 - Another distraction. This time it was checking out the W6MIT-built "1625 Rig" - a homebrew transmitter. Acquired on April 10 and had it "on the air" on the 14th.

April 15, 2018 - Back to the R-389. I double-checked some of the RF module mechanical alignments just to verify that everything was correct. Cleaned up some residual grease and splatter that I'd missed earlier. Cleaned the Main Frame bedplate. Cleaned the Veeder-Root counter and repainted the decimal point. Reinstalled the RF module into the Main Frame. This has to be carefully done because there are four cables that have to be routed through holes in the bedplate as the module is lowered into place. The position of the module has to be slightly moved so that the three bedplate captive screws thread in along with the two side screws and the one rear screw. When all six screws have been partially threaded into their pem-nut receptacles then all of the screws can be tightened. Don't over-tighten. Just snug is enough.

Mounted the front panel. The only unusual item to remember to install is the spring-loaded shaft that couples the Frequency Range switch to the mechanism that operates the dial mask. There is a steel brace that screws between the bottom of the RF module at the gearbox to the Main Frame that has to be installed. There are eight 10-32 FH screws that mount the front panel to the Main Frame that have to be installed. The motor drive power cable has to be plugged in. The two harness connectors have to be plugged into the RF module. The three antenna coax cables that come from the RF module and are routed through the Main Frame have to be plugged into the Antenna Relay Box. The remaining coaxial cable connects to the VFO.

I noticed that several of the knobs were the incorrect size for where they were installed based on the panel nomenclature size. I referenced the manual artwork and the manual front panel drawing to install the correct size knobs in their proper locations. Went to my R-390A spare knobs box to find nice condition replacements as needed.   

April 16, 2018 - Touched-up the chips on the knobs that had problems. Not all had chips. About five needed touch-up. I used black nitrocellulose lacquer applied with a small brush.

I found a correct style, good condition Line Level meter on eBay. This was cleaned up and installed. Apparently, when the original R-389 meters were removed the meters were "chopped" out with a cold chisel. On both meters, three of the mounting screw holes had paint scraped off however one hole on each meter mounting was severely "gouged" with a huge aluminum burr that prevented the meter from setting flush against the panel. I used masking tape to protect the panel and then used a file to remove the gouge's deformed metal to allow the meters to mount correctly. Once the Line Level meter was installed, the wires were soldered to the terminals. NOTE: It's odd that the original meters would have been removed for radiation since the original R-389 meters didn't have radium coated needles or scales.

More grease! This time on the VFO front gear driven switch. Also the oldham coupler was all greased up. The only reason for the grease on the oldham coupler is to hold it in place while installing the VFO. Only a very small dab is necessary on one side only. Once the greasy mess was cleaned up, the VFO was installed. I had set the frequency to 780kc (no particular reason but it's easy to remember - KOH's freq) so, since the VFO position wasn't moved and the RF module was set to 780kc, then the oldham coupler was in the correct position to allow the VFO to mount easily. The VFO is mounted with five captive screws. (I later had to actually synchronize the VFO for the correct output frequency of 470kc at 15.0kc.)

Installed the Audio Module and installed the Power Supply Module.

There was a brass blade screw used on the front panel to mount one of the resistor boards. Replaced this screw with the correct stainless steel flat head Philips screw.

Cleaned IF module as it seemed to have a light coating of oily dirt on it. Installed IF module and connected the three coaxial cables and the power input plug.

The R-389 was now ready for power-up, testing and electronic alignment.

April 17, 2018 - The Carrier Level meter wasn't the correct style. I've been unable to find a suitable one on eBay or from other sources. I decided to harvest a Carrier Level meter from a junk R-392. These meters look similar to the meter used in the R-389 but the scale is slightly different. Original meter FS was 100db and, although the R-392 meters have 100db as the highest number shown, the scale goes one more graduation beyond (or around 120db FS.) Also, the R-392 meter has "DB CARRIER LEVEL" on the meter scale where the R-390 meter just has "DB" on the scale. Additionally, the meter case is actually slightly larger. When mounted, the meter is in contact with the beveled spacer on the grab handle. It's a tight fit but it will fit. One other problem is the meter FS current is slightly different resulting in a fairly "stingy" meter reading. So, I spent a couple of hours harvesting the R-392 meter and installing it into the R-389. It was a waste of time because the very next day an original R-390 Carrier Level meter came up on eBay. When it arrives, I'll replace the R-392 meter.

photo left
: The RF module with the cover removed. The two tubes between the slug racks are the RF amplifiers. Note the motor-driven bandswitch behind the tubes. The two left-most slug racks tune the VFO and Mixer Output Stages and Output Coupler. The remaining seven slug racks tune the bands 15kc-27kc, 27kc-56kc, 56kc-128kc, 128kc-255kc, 255kc-500kc, 500kc-855kc, 855kc-1500kc. Below the slug racks are the 34 RF transformers. Four for each band (28,) four for the output coupler and two for the VFO-Mixer output. Note the threaded rods that lift the various slug racks and the associated return springs (visible in the foreground openings.) The threaded rods are gear-driven by the two line shafts that are below the RF module chassis.

Powered up the R-389  - Everything is working. Motor drive is now fast and not bogging-down at all. Manual tuning is very light and feels like a clean R-390A gear box. Seems like there's a lot more audio now. Operated the receiver for about an hour. Tuned AM-BC KOH, then went to 60kc WWVB and 24.8kc NLK. Alignment is next after several more hours of "burn in."

April 18, 2018 - Ran the R-389 for a couple of hours. I'm sure this receiver was rarely operated by its former owner. It was in a small storage room located under the house when I picked it up. I believe that getting some "hours" on it will help reveal any latent problems and should result in a better alignment.

April 19, 2018 - Aligned the IF module. 455kc IF transformers slightly off. Gained about 1 vdc on Diode Load after 455kc IF transformer adjustment. Crystal Filter off quite a bit, especially the core adjust that equalizes the output on the .1kc and 1kc positions. AGC adjustment off quite a bit. About one full turn of the adjustment to attain maximum AGC voltage. Ended up with increase of +10db on CL meter.  >>>

>>> Performed the alignment on the VFO output stage, the Injection Mixer stage and the Output Coupler stage. This requires a RF probe and VTVM to monitor the test jack level and adjust for maximum output. The RF signal generator is not required because the circuit's crystal oscillator is used as the signal source. Alignment was fairly close but still some improvement was gained. Another note,...this was a good test for the motor drive system because alignment points are at the extremes of the tuning range. Motor drive worked great with no hesitation or bogging-down - just fast and easy to go from 15kc to 500kc or from 500kc to 1500kc in about 30 seconds or less.

April 20, 2018 - Aligned First Mixer Output Transformer, Second Mixer Output Transformer and the 10,455kc Crystal Oscillator. This entire section of the receiver was out of alignment. The Crystal Oscillator requires using a VTVM to read maximum RF voltage. One adjustment is accessed from under the receiver and the RF Module brace has to be removed (just two screws.) This adjustment was quite a bit out from peak. The secondary (top side adjustment) was severely out from peak. These adjustments resulted in another +10db increase in signal level on the CL meter. The next step is to align all of the slugs and trimmers for the seven bands that cover from 15kc up to 1500kc.

April 21, 2018 - The original style Carrier Level meter arrived today in excellent condition. Didn't need any cleaning as it looked almost new. Installed CL meter using correct type of hardware. Adjusted the CL meter pot for showing +5db with no antenna (just slightly above zero.) Tuned in local AM BC station and the CL meter went up to +70db. Tuned off of station and noise level showed about +20db. Nice improvement. Still have to align the slugs and trimmers on the seven bands. Since the signal generator has to be able to produce a sine wave down to 15kc, I'm going to have to use my HP Function Generator for signal inputs below about 50kc. I'll probably switch over to the HP 606B at 50kc or so. Most RF signal generators only operate down to about 50kc, some only go down to 100kc or so. For VLF applications it becomes necessary to use a Function Generator and produce sine wave outputs as low of a frequency as required. Most Function Generators will produce wave forms as low as 1hz or lower. They are ideal for alignments and checking signal response on the VLF range and the lower LF regions. (I actually found that this HP Function Generator was very unstable at 15kc up to 50kc. Both frequency and amplitude varied so much and so quickly it was difficult to align the receiver.) April 22, 2018 - Performed the RF tracking alignment. There are two tuning ranges but there are five bands in the 15kc to 500kc range and two bands in the 500kc to 1500kc range. Each band has four slugs and four trimmers the need to be adjusted. I didn't need a spline-wrench for adjusting the slugs as with a R-390A. Just a blade screw driver, like the R-390. I used a function generator from 15kc up to 50kc. From 50kc and up, I used the HP 606B RF generator. (I ended up realigning the frequencies below 100kc using a General Radio Type 1001-A RF signal generator. This sig gen will go down to 5kc with great accuracy and stability. Made a considerable difference in the LF and VLF performance.) After the RF tracking alignment, I gained another +5db on the Carrier Level meter when tuned to a local AM BC station. Off frequency CL measures +15db and on frequency CL measures +75db. Checked NLK, the USN MSK station from Jim Creek, Washington on 24.8kc. This station measured about +20db on the CL meter. NPM (USN MSK from Hawaii on 21.4kc) also measured about +20db. Listening was all on loudspeaker.

April 23, 2018 - Adjusted R-260. This adjusts the balance on the First Mixer with one signal from the 2nd RF amplifier and the other signal from the Mixer Driver (VFO plus other stages.) This adjustment was off causing about a 2 volt increase over the minimum setting. Reduces Mixer noise.

Performance - On Wire Antenna - Late-April isn't the best time for testing on Long Wave, especially using a wire antenna, but, the testing was done at 10PM in the evening to help with signal levels and with the noise. I used the 135' CF Inv Vee with 96' of ladder line with the lines tied together. This wire antenna usually provides adequate signals although the noise level is pretty high. I tuned from about 410kc down to 320kc. I had the Audio Gain at about 5 or 6 and the RF Gain at about 7 or 8. MGC was used and the BFO was on. The Unbalanced Antenna input was used. I heard MOG 404kc very loud, it's in Montegue, CA and runs about 50 watts. Also, very loud was BO 359kc in Boise, ID. Many NDBs were heard from Oregon, like MF, OT and MEF. Canadian NDBs copied were XX, NY and DC. All pretty easy ones. Conditions were okay for late-April but the noise level was very high. The R-389 seems to be operating like a typical, high performance Long Wave receiver in that many stations can be tuned in and it is capable of decent copy even though the antenna and the conditions weren't ideal.  - April 23, 2018 Antenna Testing - When first acquired this R-389 didn't receive signals if the Balanced Antenna input was used. I wanted to test that the problem was repaired (the bent pins on the BNC connector P110 and receptacle P110.) Connected a Twin-ax to UHF coax adapter to the Balanced Antenna input and hooked up the wire antenna. Local BC station KOH was showing +75db on Unbalanced and +72db on the Balanced input so the problem was corrected.

The next test was to check the remotely tuned loop antenna operating with the R-389. When first acquired this R-389 didn't receive any signals using the loop antenna. I now connected the loop to the Balanced Antenna input and tuned to 314kc which is the frequency of a nearby DGPS node (read - "very strong signal.") The DGPS signal was received and could be tuned with the variable bias control on the loop. I noticed a significant improvement when the shield of the remote tuner was grounded to the receiver chassis. I also used the HP 606B RF signal generator (connected to a small antenna) as a signal source that could be tuned. This verified that the remote loop could be "peaked" or "tuned" to various received frequencies and that the Q of the antenna was fairly sharp. The higher Q with a sharp peak will give good signal strength with low noise since the antenna is only responding to a very narrow tuned frequency.

For more details on the R-389 performance testing, VFO end point error adjustments and other alignments go the the expanded version of this write up in the "Rebuilding the R-390A - Part 4" in the R-389 section. Use Home/Index below to navigate.


September 24, 2018 - Finally the Autumnal Equinox has arrived and conditions on LW, especially in the early mornings are improving dramatically. All summer-long, I'd perform tests on the R-389 trying various LW signals using combinations of antennae from loops to wires. Barely any signals were audible. Once in a while, the carrier of MOG 402kc in Montegue, California could be heard but usually the MCW was not audible. At night, the static crashes and other atmospherics seemed to mask all of the LW signals except for the DGPS nodes which were about the only thing that assured me the R-389 was at least receiving some types of LW signals.

With the Autumnal Equinox approaching, I began by listening in the early evening on 9/21/18, which was the day before the Equinox. Only two NDBs were heard, MOG and ULS (392kc, Ulysses, KS) and the noise was still pretty severe. I decided that in the next couple of days I would have to try early morning to see if the noise was down and maybe the signals would be up.

At 0530 on 9/24/18 I started listening using the 100'x135' "T" antenna. Right off, I tuned in ZZP 248kc from Queen Charlotte Islands, BC. Multiple NBDs were heard on many frequencies. I tuned around 390kc and heard what sounded like a voice transmission. I widened the bandwidth to 4kc (from 2kc) and at 394kc I easily copied voice weather being transmitted. With BFO turned off, I could hear in the background RWO being sent in MCW. This was the NDB on Kodiak Island that transmits TWEB or Voice Weather. In about 30 minutes of listening, I had tuned in about 30 NDBs, three of which were newly heard NDBs, ZZP 248kc, RWO 394kc and POY 344kc (#328, #329 and #330, respectively.)

I guess this illustrates that besides a quiet location, a large antenna and a superb receiver, good receiving conditions are absolutely necessary for successful LW DX copy and that my concerns about the R-389's abilities to cope with the modern LW reception issues were unfounded. As conditions continue to improve, I'm looking forward to the "peak LW reception" which will be from mid-November thru mid-January.

R-389 UPDATE: Oct. 1, 2018 - Tuned in LLD 353kc in Hawaii at 0545 this morning using 100'x135' "T" wire antenna. Also, tuned in JJY on 40kc, pulse-encoded time signal from Japan at 0615.

R-389 UPDATE: Oct 18, 2018 - LW conditions are just getting better and better. 50 stations tuned in about 45 minutes starting about 05:30. DB 341kc Burwash Landing, Yukon, CAN, FS 375kc Ft.Simpson, NWT, CAN along with ZF 356kc Yellowknife, NWT and MM 388kc Ft. McMurray, AB were some of the Canadian NDBs. LLD 353kc Lenai City, HI is a regular every morning. I'm finding that the R-389 maintains excellent sensitivity even with the Bandwidth set to 100 cycles (.1kc.) Using the 100'x135' "T" wire antenna.

R-389 UPDATE: Nov 13, 2018 - Listening evenings now that we're back on Standard Time. YY 340kc Mont Joli, QC, Canada, YXL 346kc Sioux Lookout, ON, Canada, IN 353kc International Falls, MN were some of the NDBs heard around 19:30 PST. Also heard MA 326kc Midland, TX which isn't that far away but it's on the same frequency as Canadian powerhouse DC 326kc Princeton, BC, Canada. Also, I'm noticing that I can easily tune in NDB stations between the DGPS nodes located from 285kc up to 325kc in the West. All listening was with the bandwidth set to 100 cycles. Still using the 100'x135' "T" wire antenna as the noise isn't too bad and signals seem very strong using the wire antenna.

UPDATE: Jan 10, 2019 - Some interesting conditions on MW today. I was doing some follow-up testing on the R-389 receiver after a recalibration and noticed that MOG 402kc Montegue, CA was coming in quite well  at 1530 hours PST (the sun was still high up though it was late afternoon.) A quick scan of the tuning range from 400kc down to 325kc turned up some interesting copy. QQ 400kc Vancouver Is. BC, CAN, SX 367kc Cranbrook, BC, ZP 368kc Queen Charlotte Is., BC, NY 350kc Enderby, BC and DC 326kc Princeton, BC. I've received British Columbia NDBs during the afternoon before, so that wasn't too much of a surprise. The real surprise was VT 332kc from Buffalo Narrows in Saskatchewan, Canada - during the day! Most Canadian NDBs run substantially more power than their 25W USA counterparts. Most Canadian NDBs are running between 400 watts and 1000 watts. But, Canadian NDBs use relatively small antennas just like their USA counterparts. I was using the 135'x99' "T" antenna and, unbelievably, I was listening on a loudspeaker - not a headset. Though the R-389 is an excellent LF receiver and the antenna is a pretty good performer, certainly great conditions were the primary factor in this unusual daytime reception. During the evening, I tuned in 48 NDBs in 45 minutes of listening. Tuning between 325kc and 400kc. One newly heard NDB, BK 335kc Brookings, SD (25 watt) was heard (#340 total.)

UPDATE: Sept 27, 2019 - Tested new VFO set up with R-389 performance. Listened at 0505hrs to 0545hrs tuning from 300kc up to 410kc. Logged 45 NDBs. Two newly heard Alaska NDBs, JNR 382kc and EEF 391kc. Also, copied both Hawaii NDBs, POA and LLD. Alaskan RWO TWEB Voice WX on 394kc. DB 341kc at Burwash Landing, Yukon. It's a little difficult to remember to subtract about 6kc from the dial readout for the actual frequency but otherwise the R-389 is performing very well. Sept 30, 2019 - 0510 to 0545 hrs, logged 30 stations, two newly heard, X2 328kc at Athabasca, AB and PR 218kc at Price Rupert, BC.

UPDATE: Dec 2, 2019 - I had recently bought a used Pixel Loop antenna that was providing excellent results with some of the LW receivers I tested it with. When I connected the Pixel Loop to the R-389, I didn't hear much of anything. Then, around 356kc I heard a "not so strong" carrier. Expecting to hear NY 350kc, I was surprised that the NDB was actually DC 326kc and that the R-389 was once again 25kc off due to the erratic VFO problem. When the VFO is accurately tracking as it should, the R-389 is a great performer BUT trying to keep the VFO on frequency seems to be impossible. I'm convinced that the ferrite core has some kind of problem. I strongly suspect that the continuous operation of the oven every time the receiver was in use, possibly for decades, has taken its toll on the ferrite core.

NOTE: From late-2018 up to late-2019, the R-389 has been plagued with an intermittent VFO problem. The VFO will "jump" in frequency about 25kc. Then the receiver is recalibrated for that new VFO frequency and operation is fine for about one or two months, then the jump occurs again to a new and different VFO frequency. When I got this receiver, one of the things mentioned was that the receiver didn't operate very well until it had "warmed up" for 20 minutes, then there was a sudden change and the calibration was "right on" and operation fairly normal. Once I started investigating, I found that the VFO oven was turned on and I thought the heat brought about the F change. I thought that with the oven off the temp would never go high enough for the change, so recal'ing the VFO with the oven off should cure the 20 minute wait-problem. It did seem to work but about every month or two, the F-jump happens requiring a re-cal (not real difficult but it does require VFO removal.) My thoughts are that the long-term oven-ON heat has some how changed the ferrite material. The capacitors in the VFO aren't of a high enough value to cause a 25kc F change, even if they were removed (about 280pf is required.) I've been through this VFO several times and have done the recal at least four times. My next thought is to go back to the oven-ON setup, cal the VFO at temperature and see if I can get back to how the receiver had been set up. My guess is that when it had been calibrated last (before I got it) it had been done with the oven-ON. The receiver was probably "in service" and was left turned on 24-7. This probably ended up with the VFO jumping-F problem never being experienced. Update when I actually do this recal. July 23, 2021  



Hammarlund Manufacturing Company, Inc.



 MW, LF & VLF Superheterodyne Receiver

10kc  to  540kc


SN: 20101    from 1955


When the first paragraph of the SP-600VLF-31 manual states that the receiver is unique because the tuning "extends to audio frequency 10kc" one wonders whether the writer of the manual understood the difference between 10kc of varying air pressure (sound-audio) and 10kc of radio frequency oscillation (a varying electromagnetic field.) Of course, the writer was probably thinking of a RMS voltage varying at 10kc. The SP-600VLF is not just a standard SP-600 with LF coils in the turret. It's a very different receiver that was designed specifically for longwave reception. The SP-600VLF-31 was first offered in 1954. It was the first VLF version of the SP-600 series with a later SP-600VLF-38 for 25 to 60~ AC operation being the only other version produced. The receiver shown here is from 1955 (ink-stamped June 27, 1955 on backside of the front panel.) Hammarlund also produced several SP-600VLF receivers  for the Dero Research and Development Corporation. These receivers are identical to the SP-600VLF-31 except they will have "Dero Research and Development Corp." with "Model 2F VLF Receiver" engraved on the front panel and there's a small metal etched data plate tag with the Dero name mounted below the Audio Gain control. The Dero example I saw didn't have the Hammarlund data plate mounted on the tuning condenser cover but whether that is normal for all Dero receivers is unknown.

The 1950s was a time when the radio frequency spectrum below 500kc was brimming with signals that included many voice transmissions and lots of true CW transmissions. Signals that could be tuned included airport beacons (many TWEB NDBs with voice weather reports,) maritime weather and navigation signals, ship to ship traffic, ship to shore traffic, long wave AM broadcasting from foreign lands to name just a few. Nothing like today's almost entirely data-driven transmissions that defy decoding, unidentifiable signals of all varieties and the rapidly diminishing and displaced airport beacons (Non-Direction Beacons or NDBs.) In the 1950s, the SP-600VLF would have been used in the laboratory, in commercial coastal stations or perhaps onboard ship. It was an expensive receiver that probably wouldn't have interested the average radio amateur or average radio listener. It was mainly for laboratory, commercial or military users.

Comparison to the HF SP-600s - One notices the although the receiver is obviously a "600" it has several minor physical differences. One first sees that the chassis and most of the sheet metal is gold iridite finish. Also apparent are the quite different side panels used on the VLF (similar to R-390A panels.) Another difference is the "X" option that on the HF 600 has six positions and uses HC-6 crystals but the VLF has only four positions and uses FT-243 crystals. The Carrier Level meter is also only a single scale, bakelite case unit reading "db over 50uV" while the HF 600 meter is usually a metal-cased, dual scale unit. With the dual scale meter, a switch for RF-AF is on the HF 600 that is not necessary on the VLF. A "warning" tag is mounted between the tuning dial and the logging dial  There are two additional IF cans that are smaller than the standard IF cans that are for the AVC and for the IF output. The "X" option oscillator uses a different tube. Antenna input is not on the RF platform but is terminals on a rear bracket. Note that a top cover is missing. It appears that the cover was a right-angle bent aluminum sheet metal piece that would engage into the front "pinching" two-piece retaining slot and then, resting on top of the side panels angled lip edges, drop over the side panels vertical lip edges. At the vertical rear side panel lips screws were used to mount the top cover. The cover would be easy to replicate except for the iridite finish but I have the receiver installed in a Hammarlund SP-600 table cabinet that provides the necessary protection so a top cover isn't required.

photo above: Note that most of the coupling and decoupling capacitors are ceramic disks on this 1955-built SP-600VLF.

VLF Circuit - The SP-600VLF is not just an HF SP-600 with LF coils in the turret. It's a very different receiver. First, it's not a double conversion receiver (like the HF version) but it is double preselection in that two RF amplifiers are used on all bands. The frequency coverage is from 540kc down to 10kc in six bands. 21 tubes are used in the circuit (20 tubes are used in the HF version.) The IF is 705kc and a dual crystal filter is used for selectivity. One crystal filter is ahead of the first IF amplifier and the other crystal filter is ahead of the second IF amplifier. Five different IF bandwidths are available and all positions utilize the crystal filter (the HF version uses three of the six positions for the crystal filter.) There is a 1160kc crystal oscillator circuit in the receiver but this is to heterodyne with the 705kc IF to provide a fixed 455kc IF OUTPUT to drive RTTY devices or other types of equipment that require a 455kc input signal derived from the last IF amplifier stage (full selectivity.) The audio output uses a 600Z ohm transformer that's very similar to the HF version. AVC is provided as is a BFO and there is a Noise Limiter circuit. As expected for the vintage, the 600VLF uses a standard envelope detector circuit so the RF Gain has to be reduced for proper signal to BFO injection ratio (also the AVC should be off.) The "X" function provides for only four crystal channels using FT-243 type crystals. This "X" function provides a crystal controlled oscillator in place of the LO for increased stability. With two RF amplifers and four IF amplifiers provided the SP-600VLF has a lot of sensitivity and a lot of gain - but does that really help in today's noisy LF region of the spectrum?
VLF Performance - Noise versus gain - that's the problem. Certainly the number of times that the SP-600VLF receiver will be tuned to a voice modulated carrier signal, with AVC on and the BFO off, will be very limited. AM BC at 540kc and public information BC at 530kc will be about the only AM voice signals easily received. The only other voice modulated carrier signals will be from LW BC stations. Of the LW BC stations that can be heard in the western USA only Radio Rossii 279kc was an easy station to receive. Other LW BC were extremely weak so the tuning is done with the BFO on and tune to zero beat. This is called an "exalted carrier" type of reception of AM and it sometimes helps with weak signals. Unfortunately, all I could ever hear was the carrier and the modulation wasn't detectable. 

I haven't been able to reliably receive Radio Rossii 279kc from Sakhalin Island due to a digital-data beacon that has started up on 279kc. In late November 2013 I was able to hear Radio Rossii somewhat using the 6' loop antenna but the beacon severely limits intelligibility. Radio Rossii was the only LWBC station that could be received in the west and it now appears to have a case of "chronic QRM." (Radio Rossii LW BC and all other Russian LW BC stations were shutdown Jan. 9, 2014)

Although NDBs are MCW signals, all "NDB-chasers" use a BFO (tuned to ~ 400hz offset +/- from IF) to help locate the NDB carrier and then tune to zero beat to copy the MCW (this method results in a nice sounding 400~ note depending on the particular NDB station.) Best results for NDBs has the AVC off, BFO on and riding the RF Gain control.

Nearly all operation of the SP-600VLF will be with the RF gain throttled back to 5 or 6, Audio gain at about 5 to 7, with the AVC turned off and the BFO on (I've started having the AVC on in an effort to help reduce "pops and crashes" - it helps a little bit is all.) I've found that Selectivity at 1.3kc gives the best signal to noise ratio. The Crystal Filter should be set for narrowest bandwidth (about 8 or 9 on the dial scale.) With high noise it's sometimes better to reduce the Selectivity to the narrowest bandwidth while keeping the Crystal Filter at about 8 or 9. A 600Z ohm headset connected to the 600 Z ohm audio output (not the phone jack) gives the best results for weak signal detection. The Noise Limiter and AVC circuits are not very effective on static bursts or electrical "pops" so keeping the 'phones in front of the ears is necessary during these types of conditions. I'm using a six foot remotely tuned loop antenna. Nearly all of the NDBs tuned in seem to have two or three signals on each frequency. Stations below about 100kc require an outdoor wire antenna for best reception. Stations like JJY (40kc) or WWVB (60kc) can be received with the AVC on and with the BFO off which lets the Carrier Level meter function. In this set-up you can watch the meter respond to the pulse-encoded signal that either station sends out. USN Submarine Fleet comm stations NAA, HOLT, NPM and NLK are very strong MSK Navy VLF stations in the 19kc to 25kc region of the spectrum. MSK stations will require the BFO to be on. No information can be decoded from these stations and their usefulness to LW enthusiasts is that their exact frequency is known along with their location so they provide excellent test signals for the VLF region of the spectrum.

My first serious listening session was using my 80M Inverted Vee antenna with the feed line shorted. I logged two newly-heard NDB stations. Not that they were any great DX, being PND 356kc in Portland, OR and BF 362kc in Seattle, WA, but they were new ones (#259 and #260, respectively.) Super smooth tuning with oversize controls only adds to the pleasure of using the SP-600VLF.

Chronic Dial Slippage - All SP-600 receivers mechanically drive the tuning using the same set up. A brass drive wheel is rotated with the Tuning knob. This wheel in turn drives, by friction, a brass reduction wheel that is spring-loaded against the drive wheel. The reduction wheel is grooved and mates with the Logging dial driving it, by friction, at its perimeter. If contaminates are allowed to accumulate on the friction drive surfaces eventually dial slippage will be the result. Although some SP-600 enthusiasts believe that the "S" spring used for loading the reduction wheel causes the slipping, I've seldom had just the spring be responsible for dial slippage. Almost always, dirt and grease will have collected on the friction surfaces of the brass wheels or on the rim of the Logging dial and this is what is causing the slippage. Thorough cleaning is necessary to correct the problem. Fortunately, all parts are accessible without any disassembly. The brass wheels and be accessed with the receiver on its side and the Logging dial rim can be accessed from the top. Clean all friction surfaces with denatured alcohol. I use several Q-tips to clean the brass wheel surfaces. Repeat the cleaning until the Q-tips don't turn black. On the rim of the Logging dial, I use a small piece of paper towel that is dampened with denatured alcohol. Again, clean until the towels don't turn black. Remove and check the "S" spring. It should be straight or slightly bent out. If it's bent inwards then the spring load will be somewhat reduced. You can expand the "S" spring by just bending it outwards with your fingers. Reinstall the "S" spring. As an added help, lubricate all of the shaft bearings with a drop of 10W machine oil. Also, check that the Dial Lock is completely open and not "dragging" on the Logging dial. Check the SP-600 tuning now. It should not slip and should be "velvet smooth."

UPDATE: Jan. 1, 2018 - The slipping dial is back. Although I haven't pulled the receiver out of the cabinet I can see what I think is the problem. The logging dial rim has a small gouge that I think is causing the slippage since this "dent or gouge" changes the dial friction in the drive wheel groove when the gouge comes around. I also noticed that the logging dial has a significant bend so it isn't really engaging into the drive wheel groove with the same "fit" each revolution of the drive wheel. To repair this will be a receiver out of the cabinet and front panel off since I'll have to dismount the logging dial for straightening and repair of the gouge. I'll do this after the Longwave season is over - probably around March.

UPDATE: May 1, 2018 - Slipping dial issue required pulling the receiver out of the cabinet and then disassembling to the point where the front panel could be removed. The dial lamp assembly over the logging dial has to be removed. Then the three screw mounting plate is removed and the logging dial can be removed. Close inspection revealed that near "45" on the dial rim there was a deformation that had a "lumpy" feel to it. Also, between "50" and "55" was another rough area. I carefully dressed these areas with a very fine file. The dial also had a warp that was easy to take out with minor flexing of the dial. Upon reinstalling the dial on the hub, I found that the slipping was still happening in the same areas. I readjusted the "S" spring for a greater load against the drive wheel. No improvement. I thought about how improve the "grip" of the brass against brass surfaces and came up with using rosin. I dissolved some powdered rosin in some denatured alcohol to make a thin (viscosity like water) mixture. I used a small paint brush to apply the rosin mixture into the drive wheel groove. Then I rotated the logging dial to transfer some of the rosin mix to the rim of the dial. I let the mix dry (alcohol evaporates.) That did it. No more slipping - at all! I didn't need much rosin-mix, just a little brushed just into the drive wheel groove worked great. If the rosin somehow disappears from the drive wheel groove in the future, it's very easy to reapply the rosin-mix. Hopefully, the "grip" will last for quite awhile. NOTE: Very slight slippage noted in 2020. The rosin-mix probably should be reapplied each year for best results. For an update on the rosin/alcohol mix read the update for Jan 6, 2021 further down this page.

Also, during this rework that required removing the front panel, I noticed that the gray rubber boots over the toggle switches had deteriorated to the point where two of them ripped and came apart. Fortunately these rubber boots are still being made by the same manufacturer and using the same part number. I ordered a new set of four gray boots from Grainger via their eBay listings. The price was $4.50 per boot. The boots are for 15/32"-32 toggle switches and are manufactured by APM HEXSEAL (part number is IN1030.) I know these aren't original but I think these additions improve the front panel appearance and aren't serious deviations from originality.

photo above: The carrier level meter is unique to the SP-600VLF

photo above: Only four crystal positions are offered in the X option

photo above: Tag between the tuning and logging dials

UPDATE: 630M QSO with NO3M from Pennsylvania - November 5, 2018 - I had a sked with NO3M on 473kc at 1900 PST. I didn't think I'd be able to hear Eric since his QTH was in Pennsylvania - I've never even heard a NDB from Pennsylvania! Total surprise when I heard "CQ CQ CQ de NO3M NO3M NO3M K." Eric's signal wasn't strong, maybe S3 but it was Q5. I answered the CQ but Eric couldn't hear me. I was using the Hammarlund SP-600VLF and the six foot remotely tuned loop. My transmitter was the ART-13A with CU-32 loading coil to a 163' End Fed Wire. I was amazed that I could actually copy a ham signal that originated almost on the East Coast. As mentioned above,...the SP-600VLF is sensitive and it seems to work well with the remotely tuned loop antenna. I did have a successful two-way QSO with NO3M on December 7th.

photo above: The unique, iridite-finished side panels of the 600VLF

Conclusions - Medium Wave and LF Amateur Operation - NDBs are going "off the air" in droves. LW BC stations are almost totally gone. Loran-C is "long-gone." The spectrum below 500kc is rapidly becoming exclusively data transmissions that require special equipment or computer programs to decode. Nowadays, the SP-600VLF might have become a high-quality receiver that could be used to hear just a few interesting signals. Fortunately, now there are some MW and LF amateur bands that can present a real challenge for the SP-600VLF. 

Amateur operation on 472kc to 479kc (630M band) requires UTC approval for ham operations. Regulations allow CW and data with 5 watts EIRP.  As of March 2018, I've been successfully using the SP-600VLF as the receiver in my 630M station. I'm using a six-foot remotely tuned loop antenna for reception. The station is described in detail with photo in the section "Operating Vintage Gear on 630 Meters" further down this webpage.

The SP-600VLF is a "top notch" LW receiver but it's possible that some users may become frustrated by its performance in the high noise level areas that plague many LF enthusiasts. Unless your QTH is in a rural, RF-quite area, special antennas are going to be necessary for practically any receiver that tunes below 500kc and the SP-600VLF is no exception. The user's ability to hear LF signals will benefit greatly by employing a noise-reducing antenna system which generally means using a loop of some kind. In RF-quiet areas, various types of wire antennas can be used,...sometimes,...depending on receiving conditions which are dependent on the time of year and time of day. Loops don't provide stronger signals but they do provide a quieter noise level in the receiver that allows hearing somewhat weaker signals. The improvement is in "signal-to-noise" ratio and even better noise reduction can be experienced using a shielded magnetic loop.

2020-21 LW Season - Moving and Testing the Pixel Shielded Magnetic Loop Performance with the SP-600VLF-31 with weird results - I obtained this used Pixel Loop antenna in November 2019 and only tried it once with the SP-600VLF receiver before switching it over to the RACAL RA-17C-12/RA-237-B combination receiver and low frequency converter. Performance was so good using the Racal, I didn't go back to the SP-600VLF all of the 2019-2020 LW Season. I wanted to give the SP-600VLF a try this coming season and see how it responded to using the Pixel Loop. For some reason I thought it would be a good idea to have the SP-600VLF downstairs for convenience when using it in the early mornings or late at night. I set up the SP-600VLF and Pixel Loop downstairs on August 17, 2020 which typically is still too early for LW DX reception. As a test, the next morning (0550 hrs) I did a quick frequency check on MOG 404kc and found it was barely audible. No other NDBs were heard at that time. I don't expect much in LW DX reception until at least mid-September but MOG should be strong whenever it's dark out. Subsequent tests were also devoid of much in the way of MW signals. I got to looking at the room I was setup in. The entire wall to the East and North was filled with metal boatanchor radios (really nice ones,...on display shelves.) Additionally, I was at ground level. I'm pretty sure that the large amount of "metal" and the lack of height probably was the reason for no signals. I returned the Pixel Loop back upstairs and it performed normally with the RACAL setup. I left the SP-600VLF downstairs for the time being.

Jan 3, 2021 - Maintenance Required - I moved the SP-600VLF back upstairs with the intention of setting it up with the Pixel Loop for further testing. Earlier, I had been noticing that changing the SELECTIVITY would cause signal loss and erratic reception. The problem turned out to be in the SELECTIVITY switch that apparently I'd never cleaned. De-Oxit and a small paint brush (and cleaning out a few spider webs) got the switch operating fine. This seemed to clear up the problem. Also noted that for quite a while now the dial is again slipping. Not nearly as bad as before but it is getting worse. More rosin/alcohol mix needs to be applied to the drive wheel.

Pixel Loop Problem - Unbelievably during some equipment moving the day before (Jan 2, 2021,) I apparently hit the toggle switch that turns the Pixel Loop on and off while installing a piece of gear on the same table. I never even noticed that I had hit the switch box. At any rate, the next night I intended to try the Pixel Loop with the SP-600VLF but the toggle switch handle just "flopped" around and apparently was broken internally. It's a DPDT mini-toggle like those made by C&K. Replacement necessary. I thought I had several of these types of switches but an extensive search proved that I didn't even have one. They aren't hard to find, in fact, Dayton ham KB6SCO had about 50 of them, so we did a mutual trade of small items we each needed. The switch R&R was no problem and the Pixel Loop was back up and running for the evening of Jan. 5. Though I must have copied 50 NDBs between 320kc up to 400kc, including POA and LLD from Hawaii and YEK from Nanuvat along with many mid-western NDBs and Canadian NDBs from Ontario and Quebec, not one NDB heard was a "newly heard" one. Performance was excellent with both the Pixel Loop and the SP-600VLF - except for the slipping dial. It's getting much worse.

UPDATE: Jan 6. 2021 - The rosin mix was still working fine in the small groove of the idler wheel that actually drives the dial. The beveled drive wheel that interfaces with the idler wheel was where the slipping was happening since I hadn't ever applied the rosin mix there. I cleaned the bevel with alcohol and several Q-tips turned black indicating dirt or contamination of some type. Just cleaning the bevel gear helped with the slipping but I applied new rosin/alcohol mix to ALL drive surfaces this time. After the rosin mix dried, no slipping. Just as another precaution, I adjusted the spread of the "S" spring for the dial drive. This increases the engagement force of the idler wheel into the bevel of the drive gear. The dial drive now seems excellent with no slipping. We'll see how long this lasts.

Other minor stuff,...the former owner of this SP-600VLF had added a standard phone jack to the rear chassis apron for easy connection to the 600Z line. The mechanical workmanship was barely acceptable but the wiring was not even close to acceptable. Just a sloppy job with burned wire insulation and gloppy solder joints. I replaced the burned insulation wires and cleaned the terminals of the excess solder.  The joints were resoldered with minimal solder for a better connection that was neater in appearance.

The bottom chassis cover was bending due to it not clearing the garolite insulator that had been used for the phone jack installation that had to have the jack insulated from the chassis. The insulator had to be removed and trimmed on three sides by .250" to prevent interference with the bottom cover installation and to generally have a neater appearance. After the trim, the bottom cover fit correctly.

Interesting: Jan. 7, 2021 - 1925hrs PST, while listening on the SP-600VLF with the Pixel Loop. I was tuning the 630M band and was surprised to hear a "beacon." It was actually a ham propagation beacon sending CW at about 10 WPM. "WA4SZE/BEACON" was the message. RST about 539. WA4SZE is located in Manchester, Tennessee which would be good DX for a NDB but it's really good DX for a ham beacon.

Another Beacon - Mar 2021 - WB6ZBX Jeff in Fresno, California has set up an old Nautel NDB transmitter to operate on 478kc. Jeff has modified the Natel to operate mode A1 rather than A2 (MCW.) The power output is 125 watts to an inverted "L" antenna with an external matching network. The antenna is 55ft vertical and 90ft horizontal. The Nautel is on a timer and only operates from 1730hrs to 1830hrs Pacific Time and from 2100hrs to 2300hrs Pacific Time, every day. The beacon sends "de WB6ZBX/B" every 10 seconds. I've copied WB6ZBX/B here in Dayton, Nevada at about RST 559 using the SP-600VLF and the Pixel Loop.

Another Beacon - September 2, 2021 - N6NKS, Steve McGreevy of is operating a 630M beacon on 474.7kc in the A1a mode. The transmitter is homebrew and the antenna is a 24ft tall vertical with C-hat. I copied N6NKS at 0550hrs in the morning. RST was 549. I was using the SP-600VLF and the Pixel Loop.





RACAL Communications Ltd


RA-17C-12 Receiver with RA-237-B  L.F. Converter


980kc to 30mc Standard RA-17 Coverage

10kc to 980kc with L.F. Converter




RACAL Engineering Ltd was a British company that was founded by Raymond Brown and George (Jock) Calder Cunningham in 1950. The company name was derived from the names of the founders RAy Brown and Geo. CALder Cunningham. In 1953, the British Royal Navy wanted Racal to build a couple hundred Collins 51J receivers for RN use. Racal wanted to use mostly British parts but Collins insisted that parts from the USA had to used. After an inspection of the (then) small Racal manufacturing facility, Collins refused to license the manufacture of the 51J by Racal. Dr. Trevor Wadley was called to help design a new receiver that would have the specs of the Collins 51J but be a new original design. The "Wadley Loop" was a method of using a fixed crystal oscillator and a VFO combining in three mixers with harmonics from the crystal oscillator and the incoming signal to create a "drift cancelling" circuit.

Although the Wadley Loop might be the "heart" of the RA-17, it's the elaborate Antenna-RF preselector circuit that allows the receiver's performance to be maximized for any frequency or antenna used. The preselector has a very Hi-Q and has six tuning ranges plus a variable tuning control. This allows exact tuning of the RF amplifier grid input which results in the absolute best transfer of antenna energy to the receiver's front end. The film-strip tuning dial is six feet long and covers 1000kc divided into 1kc divisions. Dial accuracy is to the kilocycle. 100kc calibrator, triple conversion, six selectivity positions from 13kc down to 100hz, +/- 8kc BFO, long-short AVC, RF/AF/S-unit meter functions, 22 tubes (23 tubes in UK version,) four AF outputs with a 3Z ohm 1W audio for external loudspeaker (USA and MK.3 versions,) built-in monitor speaker (with off switch,) 100kc IF output were some of the features on the RA-17 receivers.  

The RA-17 was the first successful receiver to employ the "Wadley Loop" system for oscillator and conversion stability. The first British Royal Navy RA-17 receivers supposedly cost £ 300 each, an equivalent cost then of about $1500. The RA-17 was produced from around 1957 up to around 1973. The RA-17 was upgraded several times but also many variations were produced that were built for special purposes or to be used with other specific equipment. The RA-17 C series was built for North American use with standard US-type tubes and US-compatible hardware. 

Racal also produced many different types of accessory equipment for the RA-17, e.g., VLF/LF/MF converters, digital frequency readouts using Nixie tube displays, panoramic adapters, SSB adapters, diversity equipment, RTTY equipment and many other devices. Racal's official name changed several times over the years. Starting out as Racal Ltd, then Racal Engineering Ltd, then Racal Communications, etc., many variations. At one time, Racal employed 30,000 workers building many different types of electronics (not just radio equipment.) It was the third largest electronics firm in Britain and had facilities in 110 different countries. Calder Cunningham died in 1958 and, in 1966, Ray Brown accepted a political position in British government Ministry of Defense, retiring from the company. After 1966, Ernest Harrison was in charge of Racal. The company also owned Decca, Chubb and Vodafone to name a few of their holdings. Several reorganizations and division sales occurred in the 1990s and, in 2000, Thomson-CSF (aka Thalen Group) purchased the bulk of Racal Electronics.

L.F. Converter Type RA-237-B Circuit - There was a RA-137 LF converter that proceeded this later version, the RA-237-B. This version was designed to work with either the RA-17 or the RA-117 receivers. The "B" indicates that this LF converter was built in England for North America-use and was equipped with USA-type tubes, hardware and connectors.
The RA-237-B LF converter is connected via a coaxial cable to the 1mc crystal oscillator of the RA-17 using the BNC connector marked "1mc" on both units. The 1mc oscillator is then routed to a LF Harmonic generator and to a 2mc bandpass filter that passes the second harmonic of the 1mc oscillator. This 2mc signal is combined in the converter's Mixer stage along with the RF Amplifier output. The output of the converter's Mixer is essentially a tunable 2-3mc signal that is connected to the RA-17's 2nd IF amplifier which is also tunable 2-3mc. The 2-3mc signal is then routed through the remaining RA-17 circuitry. LF tuning is accomplished with the Kilocycle tuning on the RA-17 referencing the "red scale" on its tuning dial. The Megacycle tuning of the RA-17 is not active when the converter is being used so the position of the Megacycle tuning is not important. AVC from the RA-17 is wire-connected to the RA-237-B and controls the RF Amp if desired. Manual gain control can also be used. HT1 and HT2 are +250vdc routed from the RA-17 (wire-connected) through the OPERATION toggle switch of the RA-237-B to allow selecting either RA-17 normal operation (980kc-30mc tuning) or RA-17 + RA-237-B operation (10kc to 980kc tuning.)
Operation - With the RA-17 turned on and the RA-237-B power on, select "10kc to 980kc" with the OPERATION toggle switch. Using the Kilocycle tuning and observing the red scale on the RA-17 dial select a frequency, e.g. 350kc. On the RA-237-B, using the ANT RANGE switch, select 210kc to 500kc range. Using the RA-237-B ANT TUNING, adjust the dial to read approximately 350kc. As you near 350kc, the background noise in the RA-17 will increase and will peak somewhere near 350kc as read on the RA-237-B dial. As you search for a NDB station with the RA-17, peak the RA-237-B every 5kc or so. The converter's preselector circuit has a very high Q and the tuning is very sharp. The frequency is read directly on the red scale of the RA-17 and the approximate antenna peaking frequency is read on the RA-237-B dial. With very weak signals, switch off the AVC and control the front end gain manually. This will prevent the noise level from controlling the AVC and reducing the front end gain. Manual control also is necessary during very noisy conditions. The Hi-Q ANT TUNING is narrow enough to reduce a lot of the LF reception noise in most cases and AVC can be used during good conditions and moderate signal levels. If you want to return to HF just switch the OPERATE toggle switch to 980kc to 30mc position and the RA-17 front end takes over and allows HF reception. Below are reception logs for the RA-17/RA-237-B combo. The first four logs are with an outside wire antenna. Remaining logs are with Pixel Loop.

Reception Log for November 10, 2019  -  2150-2215hrs PST  -  Ant 135' "T"

1. YTL 328kc - Big Trout Lake, ON, CAN
2. VT 332kc - Buffalo Narrows, SK, CAN
3. DB 341kc - Burwash Landing, YK, CAN
4. RYN 338kc - Tuscon, AZ
5. YZH 343kc - Slave Lake, AB, CAN
6. POY 344kc - Powell, WY
7. SBX 347kc - Shelby, MT
8. YXL 346kc - Sioux Lookout, ON, CAN
9. NY 350kc - Enderby, BC, CAN
10. IN 353kc - International Falls, MN
11. YWP 355kc - Webequie, ON, CAN
12. ZF 356kc - Yellowknife, NWT, CAN
13. YQZ 359kc - Quesnel, BC, CAN
14. RPX 362kc - Roundup, MT
15. YMW 366kc - Maniwaki, QC, CAN
16. ZP 368kc - Sandspit, Queen Charlotte Islands, BC, CAN
17. EX 374kc - Kelowna, BC, CAN
18. CNP 383kc - Chappell, NE
19. YWB 389kc - West Bank, BC, CAN
20. PNA 392kc - Pinedale, WY
21. YL 395kc - Lynn Lake, MB, CAN
22. ULS 395kc - Ulysses, KS
23. ZSS 397kc - Yellowhead-Saskatoon, SK, CAN
24. FN 400kc - Ft. Collins, CO
25. QQ 400kc - COMOX Vancouver Is., BC, CAN






Reception Log for November 11, 2019  -  1920-1950hrs PST   -   Ant 135' "T"

1. UAB 200kc - Anahim Lake, BC, CAN
2. LU 213kc - Abbottsford, BC, CAN
3. EL 242kc - El Paso, TX
4. XC 242kc - Cranbrook, BC, CAN
5. QL 248kc - Lethbridge, AB, CAN
6. YCD 251kc - Nanaimo, BC, CAN
7. LW 257kc - Kelowna, BC, CAN
8. VR 266kc - Vancouver, BC, CAN
9. XS 272kc - Prince George, BC, CAN
10. YYF 290kc - Penticton, BC, CAN
11. TOR 293kc - Torrington, WY
12. DC 326kc - Princeton, BC, CAN
13. MA 326kc - Midland, TX
14. RYN 338kc - Tuscon, AZ

Reception Log for November 13, 2019  -  2220-2235hrs PST  Ant 135' "T"

1. LYI 414kc - Libby, MT
2. FQ 420kc - Foremost, MN
3. ATS 414kc - Artesia, NM - 25W
4. ZQ 410kc - Sir Wilfred Laurier, Canada Coast Guard Ship, BC, CAN
5. Z7 408kc - Claresholm, AB, CAN
6. MW 408kc - Moses Lake, WA
7. YLJ 405kc - Meadow Lake, SK, CAN
8. AZC 403kc - Colorado City, AZ
9. L4 402kc - Nipawin, SK, CAN - 200W  < newly heard station #345


Reception Log for Nov. 20, 2019 from 2150-2220 PST netted 36 stations logged about 30 minutes, tuning from 326kc up to 410kc. Listed here are only the newly heard stations using the RACAL set up. Other stations heard in this session are listed in the other logs.

1. YPO 401kc - Peawanuck, ON, CAN
2. JDM 408kc - Colby, KS  25W
3. YJQ 325kc - Bella Bella, BC, CAN
4. X2 328kc - Athabasca, AB, CAN
5. YY 340kc - Mont Joli, QC, CAN
6. XX 344kc - Abbotsford, BC, CAN
7. PA 347kc - Prince Albert, SK, CAN
8. LLD 353kc - Lenai City, Hawaii
9. AL 353kc - Trina, WA
10. ODX 355kc - Ord, NE  25W
11. YAZ 359kc - Tofino, Van Is, BC, CAN
12. SX 367kc - Cranbrook, BC, CAN
13. DPY 365kc - Deer Park, WA  25W
14. AA 365kc - Fargo, ND


11-10-2019 - Cndx were very good with fairly low noise
11-11-2019 - Cndx noisy probably due to the time I was listening
11-13-2019 - Cndx were very good with fairly low noise
11-20-2019 - Cndx were very good with low noise

Total NDBs logged with a wire antenna - 61

Antenna for these four sessions was the 135' "T" which is an 80 meter Inv Vee fed with 99' of ladder line with the ladder line wires tied together and connected to the center conductor of the Antenna Input of the RA-237-B.


NOTE: I've checked 630M (472kc to 479kc) several times and have only heard JT9 signals, no CW signals,...yet.

Performance - The RA-17 and RA-237-B combination works amazing well for LF reception. The reception logs show NDB stations received with a wire antenna which usually presents a fairly high noise level. However, the very Hi-Q of the preselector in the RA-237-B helps to reduce noise as does the double conversion scheme. None of the listening sessions were longer than 30 minutes and the total NDBs tuned in was 61 stations (RYN 338kc is listed in two sessions.) The 200kc to 300kc region has a higher noise level and also fewer operating NDBs which accounts for the fewer stations in that log. Tuning only 18kc of the 400kc region produced nine NDBs, one of which was a newly heard NDB (L4 402kc,... #345.) I'd have to rate the RA-17 and RA-237-B as a really fine set-up for LF listening. The manual specs the sensitivity for the combo at 1uv for A1 and 3uv for A2 which is certainly believable, although noise levels in the MW, LF and VLF regions don't allow reception of signals at that level of sensitivity. I'm sure with a noise reducing antenna such as a "tuned loop" even better DX could be achieved. But still, the wire antenna performance is impressive. Frequency readout is right-on, amazing accuracy but, like the R-390A, you have to add or subtract the BFO setting. 600Z phones were plugged into the front panel jack(s) for reception.

UPDATE Nov 30, 2019 - I've started using a Pixel Technologies Shielded-Magnetic Loop antenna with the Racal LF combo. So far, the performance of the loop has allowed receiving NDBs east out to Quebec and west to Hawaii. More details as more testing is completed. The Pixel Loop is profiled in the "Loop Antenna Designs" section in Part 4 of Vintage LW Receivers.

UPDATE Dec 6, 2019 - Below is the reception log for Dec 5, 2019 using the RACAL RA17/RA237B with the Pixel Loop. The loop was indoors (second floor) and pointed NE. Conditions were great. 28 NDBs logged in a 25 minute session. One newly heard station, YFM 332kc LaGrande, Quebec, #347. I also logged another newly heard station with the Pixel Loop/RACAL setup a few days earlier, PMV 329kc Plattsmouth, NE, #346

Reception Log for Dec 5, 2019, 1905hrs-1930hrs PST using Pixel Loop


1. YWB 389kc - West Bank, BC,CAN
2. PNA 392kc - Pinedale, WY
3. TW 389kc - Twin Falls, ID
4. JW 388kc - Pigeon Lake, AB, CAN
5. HAU 386kc - Helena, MT
6. QV 385kc - Yorkton, SK, CAN
7. PI 383kc - Tyhee, ID
8. MR 385kc - Monterey, CA
9. GC 380kc - Gillette, WY
10. YE 382kc - Fort Nelson, BC, CAN
11. EX 374kc - Kelowna, BC, CAN
12. YBV 370kc - Berens River AP, MB, CAN
13. AA 365kc - Fargo, ND
14. SX 367kc - Cranbrook, BC, CAN
15. ZP 368kc - Sandspit, Queen Charlott Is., BC, CAN
16. DPY 365kc - Deer Park, WA
17. RPX 362kc - Roundup, MT
18. YQZ 359kc - Quesnel, BC, CAN
19. ODX 355kc - Ord, NE
20. IN 353kc - International Falls, MN
21. PG 353kc - Portage, MB, CAN
22. NY 350kc - Enderby, BC, CAN
23. YXL 346kc - Sioux Lookout, ON, CAN
24. YZH 343kc - Slave Lake, AB, CAN
25. YY 340kc - Mont Joli, QC, CAN
26. RYN 338kc - Tuscon, AZ
27. ZU 338kc - Whitecourt, BC, CAN
28. YFM 332kc - LaGrande 4, QC, CAN < newly heard station #347

Reception Log for Dec 8, 2019, 1910hrs-1940hrs PST using Pixel Loop - 27 stations received (only stations not listed in previous logs are shown)

Reception Log for Dec 10, 2019, 1905hrs-1935hrs PST using Pixel Loop - 22 stations received  (only stations not listed in previous logs are shown)

1. ZZD 308kc - Edmonton IAP, AB, CAN
2. YIV 300kc - Island Lake, MB, CAN
3. Z1 305kc - Three Hills, AB, CAN 25W < newly heard station #348
4. UNT 312kc - Penticton, BC, CAN
5. YQF 320kc - Red Deer, AB, CAN
6. LGD 296kc - LaGrande, OR 25W
7. YER 334kc - Fort Severn, ON, CAN 195W < newly heard station #349
8. YLD 335kc - Chapleau, ON, CAN
9. MEF 356kc - Medford, OR

Total NDBs logged with RACAL setup - 94 (Nov 11 to Dec 11, 2019)

1. YNE 207kc - Norway House, MB, CAN 1KW < newly heard station #350
2. IB 209kc - Atikokan, ON, CAN
3. RL 218kc - Red Lake, ON, CAN
4. YKA 223kc - Kamloops, BC, CAN
5. CG 227kc - Castlegar, BC, CAN
6. BR 233kc - Brandon, MB, CAN
7. XE 257kc - Saskatoon, SK, CAN
8. ZSJ 258kc - Sandy Lake, ON, CAN
9. GEY 275 - Greybull, WY
10. NM 278kc - Matagami, QC, CAN
11. CEP 278kc - Ruidoso, NM
12. QR 290kc - Rigina IAP, SK, CAN

Using Selective Level Meters as Longwave Receivers

Rycom R1307A/GR  SN:538 - as acquired, it looked good,...from a distance. Obvious cosmetic problems are the National HRK tuning knob, a couple of incorrect bar knobs, a front panel "creamy white" repaint that oversprayed most of the screw heads and an oxidized spray-on clear-coat over all of the knobs. Several weak tubes, worn dial gears and alignment issues were the electro-mechanical problems found.

Selective Level Meters (aka Frequency Selective Voltmeters, Wave Analyzers or SLMs) are test instruments that incorporate a sensitive tunable radio receiver that usually features selectable modes of detection, bandwidth filters and attenuators with an output that drives a calibrated analog meter. Usually SLMs also have an audio output stage for aural monitoring purposes. SLM instruments were used for a variety of purposes such as measuring signal leakage on cables or interference on transmission lines, some SLMs were used to measure field strength from transmitters (or parasitics or harmonics from transmitters,) some SLMs even provided a built-in calibrator to assure accurate measurement of received signal levels. However, NONE of the SLMs were designed specifically just as Longwave receivers. It's just part of the design of many SLMs that a fully functional receiver was necessary and many times that receiver will provide excellent reception in the MW, LF and VLF portion of the spectrum.

If you're interested in acquiring a SLM you'll have to do a little research first. There are some types of SLMs that won't work very well at all as LW receivers. A good example of an unusable SLM is the common Sierra Electronics Corporation Model 125B. This is a vacuum tube model Frequency Sensitive Voltmeter. I have an example that's fully operational with a good set of tubes and I have performed a full alignment on the instrument. However, the Model 125B doesn't have a BFO to help locate weak NDBs and this makes it almost useless as a LW receiver. A BFO is absolutely essential because virtually ALL signals below 500kc are CW, MCW, MSK, Pulse Encoded, etc. Only the few TWEB NDBs and the very few LW BC stations left will have Voice transmissions. Without a BFO, you'll hardly hear any signals below 500kc. Another example of an ineffective SLM was a Cushman that was loaned to me by fellow ham and LW enthusiast, K7SSB. The Cushman was a solid-state model that did have an on-board BFO with USB and LSB capabilities. It didn't matter, I couldn't pick up any signals using it. K7SSB was also disappointed with the Cushman's performance as a LW receiver and he eventually sold it on eBay. But,...on the other hand, the following are a some SLMs that work great as LW receivers,...

One SLM that's a "standout" both in looks and performance is actually labeled that it's a "Radio Receiver." It was built by Rycom for the U.S. Navy. Rycom is the trade name for Railway Communications Inc., a company that built (and still builds) many types of measuring and locating devices.

Rycom R1307A/GR - Radio Receiver

Circuit - The U.S. Navy wanted a rack mount version of Rycom's portable SLM, the Model 2147A, so Rycom produced the R1307A/GR for the Navy. The R1307A/GR is a well-known and great performing SLM that really acts more like a radio receiver. It even has "RADIO RECEIVER" engraved on the front panel,...probably because 95% of the circuitry IS a radio receiver. The circuit is superheterodyne with a 2215kc IF. 17 tubes are utilized with four of those being nuvistor-type tubes (2-6CW4 and 2-7586.) Also, two transistors and several solid state diodes are used in the circuit. Frequency coverage is from 3kc up to 800kc in five tuning ranges with AM, USB, LSB, BFO and FM mode selections available. A single RF amplifier (called a Video Amplifier) acts as a cathode follower using a 7586 nuvistor tube. The Mixer is also a 7586 tube. Four IF bandwidths can be selected, 1kc, 2kc, 4kc and 8kc with each bandwidth determined by individual crystal bandpass filters. Three stages of 2215kc IF amplification are utilized. Separate detectors are used with an AM detector, product detector for SSB and CW signals and a discriminator-limiter for FM signals. As expected, no AVC is used since this is measuring device so the input signal level has to be controlled with the attenuator. There's an external audio output that's 600Z impedance, a built-in loudspeaker that can be switched on or off and a 'phones output on the front panel. Audio output is provided by push-pull 6AQ5 tubes. The large arced (and illuminated) dial features a two-speed vernier control of the tuning. The entire chassis is covered with a perf-metal housing.

Matching Antenna Z to Input Z - The R1307A/GR has a very high input impedance of  3000 ohms but that's because the INPUT is capacitively-coupled directly into the LP filter and attenuator before going to the RF cathode follower (called a Video amp) and Mixer stages. The Hi-Z input should be expected for a "volt meter" since you wouldn't want to "load down" whatever signal source you intended to measure accurately. But, for finding and measuring field strength or locating parasitics one would think that there was an external impedance matching device or a set of specifically "tuned" antennas for use as a calibrated field strength measuring device. However, nothing is mentioned in the USN manual (NAVELEX 0967-422-2010) about matching the antenna Z (or even the signal source) to the input Z.

Since the object nowadays is to use the R1307A/GR as an effective radio receiver the input Z should be matched to the antenna Z for best transfer of RF energy. Most antennas are going to have a much lower impedance than 3000Z, even end-fed wires. It's certainly possible to make a small balun with a high ratio, something around 40:1, to allow a better match for low-Z antennas. As a test, I connected an end-fed wire balun "backwards" so the Hi-Z side went to the receiver and the Lo-Z side went to a Pixel Loop. The measured gain increase was about 20db at 500kc but below 150kc the signal response dropped dramatically. This happens even using a wire antenna (which indicates the balan isn't designed for LF or VLF.) A small preselector would be an even better addition but the LF and VLF tuning range necessary would probably require a "homebrew" type of project for such a uniquely-specific, custom device. The "un-un" as a Z-match works fine for MW, especially with the Pixel Loop.

photo above
: Top chassis of the R1307A/GR - The four modules in the center of the chassis (with blue labels) are the four crystal filter bandwidth modules. To the right is the Product Detector and FM lim/disc module. The strip in front of the Prod Detector is the 2215kc IF amplifier module. Directly to the left of the IF strip is the shield covering the tuning condenser. To the left of the crystal filter modules are the two 7586 nuvistor tubes that are the RF cathode follower (called a video amplifier?) and the mixer tubes. The power supply is at the right rear and the audio output is at the rear left of the chassis. Note the red fabric cone of the loudspeaker (water proof.) The greenish residue next to the LP Filter appears to have been from a "stick-on" label. Trying to remove the residue would probably damage the iridite finish of the chassis.  Photo was taken after rebuild.

Reconditioning R1307A/GR  SN:538 - Front Panel Repaint - Although this Rycom R1307A/GR looked pretty good from a distance (see "as acquired" photo above) close-up the "amateurish" restoration was obvious. The tuning knob was from an old National receiver and the knobs used on the MONITOR LEVEL and BFO were also not correct. Additionally, all of the knobs had been sprayed with clear lacquer that was now beginning to flake off. The vernier drive for the tuning was loose and the dial pointer wasn't mechanically aligned with the tuning condenser. The most glaring problem was the front panel repaint. First, the color should be Light Navy Gray and not creamy white. The paint was applied while the controls and bezels were still mounted. Most of the mounting screws were just painted over. The dial bezel and the meter bezel were painted black using a brush because the restorer was too lazy to disassemble the receiver. The potted transformer and choke housings were repainted using a brush. Luckily, electronically, the chassis was all original with no modifications.

I was sure the creamy white paint had been sprayed over the original Navy Gray. This caused the engraved nomenclature to "fill" since the original fill paint was never removed. As a result, the new nomenclature fill couldn't be done in the correct manner since the engraving was already "filled." Close examination showed that a lot of the nomenclature was "touched up" and some looked like the fill was done with a brush. To repaint the front panel correctly required complete receiver disassembly to have the panel ready for stripping. I use Kleen-Strip because it doesn't contain methylene-chorlide but it actually works quite well. The white paint stripped off almost immediately. Once the non-original paint was gone I could see why the former owner had performed the repaint. The lower center part of the panel's original paint was worn down to the zinc-chromate primer so there was a large area of the lower panel that was yellowish-green. Another application removed the original gray paint down to bare metal however the engraving fill wasn't removed.

Apparently the fill paint was a durable type that was nearly resistant to the Kleen-Strip. A second application was applied only to the nomenclature and was left on for about an hour and a half. This did soften the fill paint enough that it could be removed using a brass wire brush. Even after the brush treatment, about 5% of fill was still adhering to the engraved metal sides. This last bit was removed with lacquer thinner, a dental pick and a brass brush.

Once all of the paint was removed the physical condition problems needed to be taken care of. The panel was bent somewhat. Not severe but it was noticeable. The panel was fairly soft aluminum so straightening was easy. There were lots of gouges and rack rash that had happened over the years. These had to be sanded or filed depending on their location. Final prep is to very lightly go over the entire panel with a hand sander using fine grit paper. This gave the new paint a good surface to adhere to but didn't remove any significant material.   >>>

photo left: Under the chassis. The shield at the front with the holes is the RF tuning circuit. Directly behind upper is the Mixer and RF Cathode Follower section. Directly below is the four Crystal Filter selection switches and adjustments. The rear shield covers the Attenuator circuitry, note the universal joint coupling from the front panel. The silver shielded box (lower corner) is the AC input filter.

>>> Finding the proper gray was difficult. I couldn't have the original color "matched" because the automotive paint store that used to do that sort of work had closed. Because of COVID-19 restrictions, browsing the paint isle in Lowe's or Home Depot was difficult. I tried to use the Internet to sample color chips of various spray paints but what colors were shown on the Internet ended up not being in stock at the store (even though the website said they were stocked.)

I ended up using Krylon Matte Glacier Gray* which was a little bit lighter gray than original but still fairly close. Since the panel had engraved nomenclature that had to be filled, no more than two coats could be used. The first try ended up with too much paint in the engraving so it had to be stripped off. On the second try I only applied one coat which was sufficient to impart the color but not fill the engraving with too much paint.

The nomenclature fill paint should be black so I used Artist's Acrylic in Mars Black. The technique is the paint some acrylic (thinned slightly with water) over the engraving for one control. Let the paint set for two minutes then wipe in one direction only with paper tower wrapped over a flat rubber eraser and dampened with Glass Plus. The paper towel is pre-cut into small pieces that just fit the eraser shape. I make a "stack" of them before starting the nomenclature filling. The rubber eraser gives the small paper towel piece a very flat surface and reduces the chances of pulling the paint out of the engraving. The paper towel can only be used once, then discarded and a new dampened paper towel piece wrapped around the eraser. This is repeated until the excess paint is removed and the engraving fill looks perfect. Also, excess "wipe off" paint has to be removed using a dampened paper towel to keep the panel area clean.   >>>

>>> Most of the time two applications and minor touchups are required to get the control nomenclature perfect. Nomenclature touchups can be applied with a toothpick or a small brush and final panel field touchups (if it's after the fill paint has dried) can be accomplished by carefully using a rubber eraser. Filling the nomenclature engraving is tedious work and it can't be rushed. I could only do a couple of control areas and then I had to take a break for a few hours. Once all of the engraving is filled, I let the fill paint set for a day and then wiped down the entire panel with a soft flannel cloth. Reassembly was started a couple of days later. This gives the paint a chance to cure and harden. Longer is ever better but two or three days will usually be enough for the paint to harden sufficiently for assembly.


* Krylon Matte Glacier Gray is a "Fusion" type of paint that combines primer and paint into one mix. This paint might be great for panels or metal pieces that don't have any engraving to fill. Since "Fusion" paints are primers they do have some type of "filler" in the mix. This has a tendency to have more paint than normal accumulate in the engraving making the nomenclature "fill" process much more difficult. Had it not been for the COVID-19 restrictions, I probably would have used an automotive-type paint that was custom matched to the original - although that would have required at least two trips to Reno.

Dial Mechanism Rebuild - The dial accuracy was off quite a lot to begin with. When I mechanically aligned the dial pointer with the position of the tuning condenser that moved the dial pointer even further off. That indicated that someone had performed an electronic alignment and had never checked the mechanical relationship of the dial pointer to tuning condenser's position. So, at minimum, a tracking alignment was going to be necessary. As part of the reconditioning, I disassembled, lubed and readjusted the tuning dial mechanism. The gear box was entirely dry which was probably okay when the brass gears were new. Now, with years of wear, there's a lot of clearance that can be felt when tuning. A fairly viscous grease has to be used as a damping medium which will greatly reduce "chatter" and "binding" within the worn gears and shafts. I used wheel bearing grease lightly brushed on the parts during reassembly. For severe wear, Nygel grease can be used which is made specifically for damping. With wheel bearing grease, when everything was back together the operation was smooth with no "chattering." I mechanically aligned the tuning condenser, which is mounted directly to the back of the tuning dial assembly and stays mounted as the entire dial assembly is removed from or mounted to the front panel. Switch Cleaning - All of the switch contacts appeared to be somewhat oxidized requiring detailed cleaning with DeOxit and a small paint brush.

Alignment - The manual indicates that the IF should be sweep aligned but the method described in the manual is quite different in that the input signal is at 120kc where the IF is 2215kc. This means that the IF alignment has the input signal go through the mixer conversion instead of using the IF input directly at 2215kc. The object of the sweep alignment is to maintain a broad, flat bandwidth by being able to observe on an oscilloscope the IF bandwidth curve. I've done sweep IF alignments before but never going through the mixer conversion. Usually the sweep is at the IF input with the 'scope monitoring the IF output at the detector with the sweep ramp output going to the horizontal channel of the 'scope. As expected, the Navy procedure must have used some special visual display equipment since it's not referred to as an "oscilloscope" in the procedure. With standard sweep gear, I couldn't get the IF curve to be stable enough to be sure of any alignment adjustments. Since the IF bandwidth seemed okay I proceeded onto the tracking alignment which was obviously needed.

photo above
: The R-1307A/GR after its repaint, several new tubes, dial rebuild and tracking alignment

Tracking - A RF signal generator applies 800kc to the input, the receiver is then tuned to the input signal and then the frequency of the IF output is monitored using a digital frequency counter. The LO output is dependent on an internal bias voltage but initial adjustments require an external +15vdc be applied to J6, the Frequency Control BNC. With the +15vdc applied, the digital counter reading is noted. Then the external bias voltage is removed and the internal bias control (BA) is adjusted so that the digital frequency counter reads the same frequency that it did with the external +15vdc applied to J6. Next, with 800kc input and the receiver tuned to the signal, C78 (high end band E) is adjusted so that the IF output reads 2215kc, the IF frequency. Once that's done, then the remaining adjustments set up the tracking on each band. The one inductance adjustment is set on the highest frequency band at 600kc and the tracking is set by varying the L and C for that band. The remaining lower frequency bands are adjusted at the middle of each band using the variable C trimmers provided.

The BFO had been misaligned so that zero beat was with the air variable fully unmeshed. Zero beat should be with the air variable at half mesh so that the BFO can select upper or lower sideband. The "+" the "0" and "-" indicate the direction of the apparent frequency displacement and aren't an indication of upper or lower sideband - not that there are any SSB signals being transmitted in the tuning range of the R1307A/GR anyway. However, its original use might have involved finding and tuning parasitics or subharmonics of USN SSB transmitters. Also the reason for USB and LSB modes. 

If you've used Navy manuals before and are accustomed to their cumbersome procedures then the Rycom R1307A/GR should come through the alignment with better overall performance. The Navy manual also has a few minor errors, like misidentifying the FC J6 as J5 (FM out) several times. The schematic and the alignment instructions are correct. As mentioned before, the sweep alignment requires a special "visual display unit" that apparently isn't a standard oscilloscope. It should be possible to input a sweep signal at the IF input and monitor the detector output on a standard XvsY 'scope for a typical sweep alignment but, unless there's evidence of some prior component replacements, the original IF alignment is probably fine.

Performance - The R1307A/GR will receive all of the usual LW signals. Navy VLF MSK stations and PE signals from WWVB and JJY can be received easily but for these LF and VLF signals I use a 135' "T" antenna directly connected to the input. That's really not a very good Z match and an "oversize" random length antenna can be a disadvantage as the R1307A/GR's high gain front end with the lack of any significant preselection can result in it responding to parasitics or sub-harmonics from nearby AM BC stations or other RF interferences (which was actually its original intended purpose) along with a very high background noise level. For MW I use a Pixel Loop antenna. DX NDB stations require nighttime listening. 'Phones should be used exclusively for DX reception. I've had the best results for all signals above 130kc, using the Pixel Loop with a "un-un" Z-match transformer. The Pixel Loop provides lower noise levels, increased front-end selectivity with no harmonic RFI using the loop and decent signal response. Best NDB DX was LLD 353kc in Lenai City, Hawaii (~2500 miles.) In Canada, ZP 367kc on Queen Charlott Islands, BC although this is a very powerful NDB running 1KW. All listening, so far, has been during the Summer which is when MW reception is poorest. From what's been received during midsummer, I would expect the R1307A/GR to be quite a good performer come winter. However, for best reception the antenna used must be matched to the very high 3000Z ohm input impedance.
Rycom Model 3135 - Selective Voltmeter - This is a portable solid-state SLM probably dating from the late-sixties. Since it's a portable, batteries are necessary for power although the 3135 will also run on directly on AC power. The AC power cable is the older style "test equipment" type with a three pin molded end with rounded sides. This type of AC power cable was used on some types of test equipment from the time period. Frequency coverage is from 3kc up to 1500kc in three tuning ranges. As with all SLMs, sensitivity is controlled by the attenuator. Two bandwidths can be selected, 2.5kc (monitoring) or 100hz (calibration purposes.) Modes received are AM, USB and LSB. The only audio output is via a front panel 'phone jack. Antenna connection (INPUT) is a pair of "five-way" binding posts. The 3135 is shown in the photo to the right.

The Rycom 3135 can be used as a LW receiver but there are a couple of disadvantages. First is that the bandwidth is essentially "fixed" at 2.5kc. This is a little wide for MCW NDBs and too narrow for AM BC. The IF bandwidth skirts are very steep and AM signals enter and exit the passband abruptly. The BFO is "fixed" since only USB or LSB can be selected and there's no front panel adjustment of the BFO. The dial isn't illuminated although the standard Rycom "push in for fast tuning" type of two-speed vernier is provided. Documentation is not very difficult to find.

One of the advantages of the Rycom 3135 is that it's usually not expensive. Most were used as portables and as a result they are usually banged up to a certain extent. In fact, the example shown is missing its front cover. A rough exterior doesn't seem to affect performance but some 3135s are cosmetically compromised so the prices are usually reasonable. The 3135 is very small and, being portable, doesn't weigh much,...maybe 10 pounds without the batteries installed.

As a LW receiver, the Rycom 3135 will perform adequately but there are many other SLMs that are much more versatile in modes received with better selectivity options resulting in a more pleasurable operating experience. I bought this Rycom 3135 for parts although it does function.       


Hewlett-Packard 310-A Wave Analyzer

Hewlett-Packard 310-A - Wave Analyzer  -  Wave Analyzers are SLMs and some types function quite well as LW receivers. However, many of the HP Wave Analyzers don't have a useful tuning range with the majority of models only tuning up to 50kc or so. But, HP did offer a few Wave Analyzers that featured a very useful tuning range. I happen to have the HP 310-A version which is shown in the photo to the left. The HP 310-A's solid-state receiver tunes from 1kc up to 1500kc and also has selectable USB or LSB and AM detection along with 200Hz, 1000Hz and 3000Hz selectable bandwidths. Lowest scale sensitivity is 10uv FS meter reading (maximum signal level) although using this sensitivity depends on how much atmospheric noise is present. With a tuned loop antenna, 10uv FS meter can almost always be used. During high noise periods with a wire antenna, 30uv FS provides better noise immunity. In the "Relative" measurement position the sensitivity is adjustable for best response versus noise. The HP 310-A is a late sixties to early seventies vintage (all solid-state) instrument. The mechanical digital readout is for receiver frequency while the long horizontal scale illuminates a red numeral depending on the sensitivity (max. signal) selected. The red and blue tags above the meter switch are USAF property identification tags. I purchased this Wave Analyzer at an industrial electronic equipment auction for $5.

I find that the performance of the HP 310-A is quite good. It's capable of receiving any LW signals being transmitted with conditions being the limitation. The 310-A has a much lower input Z of 50 ohms versus that of the Rycom R1307A's 3K ohms input impedance. This allows direct connection of antennas to the 310-A input without an impedance matching device. The 310-A doesn't have a noise limiter - mainly, because noise was one of the things the instrument was designed to measure. However, manipulation of the sensitivity versus the atmospheric noise seems to do pretty well for coping with the lack of a limiter. Since this is a measurement instrument, no AVC is provided, so strong signals will over-drive the 310-A, even when using a loop antenna. I watch the meter and keep the measured signal level at about 75% to 95% of FS with the Relative Gain control. Dial frequency readout is "to the kilocycle" accurate. I have received hundreds of NDBs from all over North America on my HP 310-A, from DDP 391kc in Puerto Rico to LLD 353kc in Hawaii.

The HP 301-A is such a good LW performer, I picked up another one in March 2021. I had to pay more for this one,...$20. Needs clean up/testing. More details when finished.

Conclusion - One should remember that SLMs weren't designed specifically as LW receivers and, as such, their features and performance can't compare to a "designed for longwave," high-end military LW receiver. Disadvantages in using a SLM for a LW receiver would be their lack of a noise limiting circuit or output limiter circuitry. Since the SLM function is to measure signals it can't have circuits that would affect the accuracy of level measurement. Using a low-noise antenna is almost always necessary. Sometimes selecting the minimum bandwidth available will also help to reduce noise without compromising the signal too much. Usually, SLMs have minimal front end selectivity and sometimes IF selectivity is also limited. Since AVC is rarely used for LW reception, the lack of AVC in SLM circuitry isn't really missed. The advantage for SLMs is usually their selling price. Since the SLMs are not that well-known as LW receivers, many times they are bargain-priced since they are often "lumped-in" with old test gear as virtually worthless. But, the good, usable SLMs seem to be well-known to many dealers, so don't be surprised at the asking price of sophisticated fairly modern types or for the Rycom R1307A/GR as a vintage example (mainly because the R1307A/GR IS identified as a "RADIO RECEIVER" on the front panel.) The HP 310-A is still somewhat unknown to dealers so it can be found at a reasonable price (mine was $5 at an industrial electronic equipment auction and just recently I picked up another one for $20.)

My conclusion is that Selective Level Meters and Wave Analyzers are designed for measuring RF field strength, finding and measuring RF leakage in transmission line systems, locating parasitics or harmonics from RF sources and other similar applications. Some of the SLMs are absolutely useless as LW receivers. Be sure to read up on any instrument you intend to purchase for LW reception and make sure that others have had success using it for that purpose. The first two instruments I tried, the Sierra 125B and the Cushman, were of the "useless" variety. The Rycom 3135 was barely usable but the Rycom R1307A/GR and HP 310-A are the best SLMs that I've tried and they perform very well as LW receivers.

photo right: The Sierra Model 125B Frequency Selective Voltmeter. The drum dial scale is at a "slant" because it is continuous tuning that has the scale spiral up as the drum is turned about four turns to go from 1kc up to 620kc. Lack of a BFO on the Sierra 125B makes it "useless" as a LW receiver.


Other Vintage Receivers with Some Medium Wave and Low Frequency Coverage

All but one of the receivers profiled in Parts 1, 2 and 3 were specifically designed for MW, LF and VLF coverage - generally 600kc down to 15kc. Many other receivers were offered in versions that covered a portion of either the MF or the LF spectrum. During the 1930s, many "All Wave" consumer entertainment radios for the home tuned down to 150kc because there was so much to listen to in that part of the spectrum then. Also, a few models of communication receivers were offered with limited MW/LF coverage. Some of these versions were excellent performers while others were barely adequate. The following is a short list, three receivers, that are the best performers with limited MW/LF coverage. None of the receivers listed below cover the entire "longwave" spectrum of 600kc down to 15kc. 

National Co., Inc. - HRO

Using coil sets G - 420kc to 200kc, H - 200kc to 100kc, J - 100kc to 50kc - Very good performer with long wire antenna or loop. These coil sets were generally optional equipment pre-WWII but the WWII military versions did include a complete set of coils, including those for MF/LF coverage. Of these military versions, the HRO-W and the RAS are the most common. LF coil sets can be used in any of the HRO receivers but alignment to the specific receiver is required for best performance. Double preselection (two TRF amplifier stages) are used in all coil sets for the HRO. IF is 456kc on almost all versions. Notice that there is a gap in frequency coverage from 480kc to 420kc (coil set F covers 920kc to 480kc.) This was because of the HRO's IF of 456kc. The RAS used 175kc IF and that allowed it to cover from 195kc up to 500kc without a gap in the frequency coverage (the USN wanted complete coverage in the 400kc to 500kc range which the standard HRO couldn't provide.) The RAS receiver must be used with RAS coil sets identified as coil sets 1 through 7 on a metal tag on the coil panel. Later HROs, like the HRO-50 and HRO-60, can also provide excellent performance using the G, H and J coil sets. The LW coil sets for these later receivers are a bit more difficult to find and are usually somewhat expensive because of that. Photo shows the 1940 HRO Senior.

Hammarlund SP-200LX aka BC-779


Covers 100kc to 200kc and 200kc to 400kc on the LF and MW bands, 2.5mc to 20mc on HF bands - Excellent with loop antenna, a bit noisy with long wire antenna (depends on your location.) If you can match the antenna Z to about 110Z of the receiver antenna input, noise response will be greatly reduced. Good dial accuracy. The BC-779 is probably the most popular of the military WWII versions of the SP-200 series. Some BC-779 receivers were built by Howard Radio Co. under contract. Band spread was not provided on the LF or MW frequencies. SP-200LX is the designation used for any pre-WWII or non-military version of the "200 Series" receiver. Photo shows the SP-200LX version. IF is 465kc on all versions and double preselection is used on all bands.

The earlier version of this receiver, the SP-100LX (1937-39) with the same frequency coverage, is profiled in Part 1 of this Vintage LW Receiver article.

RCA AR-88LF and CR-91/CR-91A

Covers 550kc to 73kc (550kc to 125kc on AR-88LF version) with SW coverage above 1.5mc up to 32mc - Excellent with long wire antenna or with a loop. Good dial accuracy. A heavy receiver weighing nearly 100 lbs in the cabinet. All steel construction is why. Stability was what RCA was trying to achieve and these receivers have virtually no drift. The AR-88LF versions were all sent overseas during WWII and are somewhat difficult to find in the USA. The CR-91 is the USA-built replacement for the AR-88LF but it's very rare. Photo shows the USA-built CR-91. Most CR-91s are actually the post-war CR-91A receivers that were built in Canada (RCA-Montreal.) The CR-91A receivers have gray panels and a front panel Phasing control for the crystal filter. IF is 735kc on all LF versions and double preselection is used on all bands.


Regenerative TRF Receivers versus Superheterodynes on Longwave

In the early days of wireless communications, all transmissions were on longwave. After the signing of the Alexander Bill in 1912 moved the amateur operation to 200 meters or below, experimentation into the shorter wavelengths began. Ships and navigation remained in the longwave region, (even today most navigation and submarine communications remain in the LW spectrum.) After WWI, most receivers used were regenerative detectors with two-stage audio amplifiers. Later, TRF stages were added ahead of the detector to further improve weak signal reception. As designs progressed, the superheterodyne did not immediately replace the TRF regenerative receivers on LW. At first, superheterodyne designs used rather low intermediate frequencies that limited coverage of certain segments of the LF bands. The USN RAA LW superhet receiver from the early 1930s used four different IF stage frequencies to optimize performance and provide complete tuned frequency coverage (10kc to 1000kc.)  For full LW (typically 15kc to 600kc) coverage, the regenerative receiver had no such limitations. Later LW superhet designs moved the intermediate frequency above the LW bands to give complete coverage.

Regenerative receivers have some advantages over the typical superhet receiver on LW. For example, receiver internal noise - regen sets are quiet and don't add much noise to an already noisy part of the spectrum. The frequency conversion required in the superheterodyne can create substantial internal noise in the receiver that limits its weak signal ability on longwave. Also, since a minimal number of tubes are used in regen sets, thermal noise is at a low when compared to a large tube-count superhet. The regen set's ability to be set-up as an Autodyne Detector, that is to produce an oscillating condition without a BFO, is also an advantage. With a superhet it is necessary to use the BFO to set-up a condition where the carrier can be heard however the BFO in a superheterodyne can sometimes mask weak signals. Though most BFOs are very lightly coupled in early superhet receivers to prevent "masking" this is not always the case in modern receivers. Additionally, when the regenerative set is oscillating, it is doing so at the tuned frequency while a superhet, using a BFO, is actually providing an audible heterodyne by injecting an oscillator signal at the detector that is somewhere near the intermediate frequency. It is the level of the injection that is important to weak signal copy. BFO frequency drift can also be a problem not found on regen sets. >>>

photo above:
   1923 RCA-Wireless Specialty Apparatus Co.  IP-501-A during a LW performance test. The receiver is powered by a Lambda 6vdc 4A power supply and a RCA Duo-Rectron regulated B+ power supply. The -C bias is supplied by three AA batteries in series. The antenna used is a 80M ham inverted vee with the feed line shorted. Since the regenerative detector is set to oscillate for NDB copy, some RF energy will couple back to the antenna. By wrapping a pick-up wire around the antenna lead-in, a digital frequency counter can used to provide an accurate frequency readout. This set-up only works while the detector is oscillating (autodyne.) The IP-501-A is tuned to local NDB "NO" from the Reno-Tahoe Intn'l AP (NOTE: NO 351kc was decommissioned in 2013.)

>>>  Lack of Automatic Volume Control (AVC) in the regen sets is also an advantage as a high noise level can capture the AVC and decrease sensitivity. Normally, with vintage superhet receivers, most CW listening is done with the AVC off  for that very reason. Most superhet communications receivers will provide switchable AVC. However, some modern receivers, especially SWL portable types, do not have a switchable AVC provision leaving the listener at the mercy of atmospheric noise. Selectivity can be be achieved by use of audio filters in later sets or by advancing the regeneration control to the point where oscillation just begins in earlier receivers. Many early receivers also provide a coupling control for selectivity (and for setting "critical coupling" for optimizing the ratio of signal to regeneration at the detector.) By using the ear and listening for a particular tone frequency our own brain can be a very effective filter although this does require some practice to become proficient at. Another habit that old radio ops had was to copy using earphones. This will allow hearing  weak signals that are at the "noise level" - of course static bursts can be almost painful at times when using early sets without limiters. Most WWII USN LW receivers will have audio output limiters that function very well at keeping static bursts at a manageable level. More common (and modern) "clipping" noise limiters don't seem to work as well as Output Limiters and will allow "pops" and static bursts through. This is because the clipping noise limiter works on repeating pulse patterns - like auto ignition noise - rather than acting on a single, quick, intense pulse. An easy method to preserve your hearing is to keep the 'phones slightly in front of the ears. Notice in vintage photos of USN radio ops that the phones are always in front of the ops ears. This method has been used by experienced CW ops since the early wireless days (when static bursts were just about the only "loud" signals heard.)

One of the best LW receivers was the RBA series built for the Navy during WWII. These receivers use three cascade TRF amplifiers feeding a non-regenerative triode detector followed by three audio amplifiers - in essence, the typical TRF receiver of the late twenties. However, that's where the similarity ends. The RBA also uses a "tracking" BFO that tunes via an additional ganged section of the five-gang tuning condenser. This allowed the BFO to always be 1kc above the tuned frequency and provide the heterodyne necessary to demodulate CW. Also, the RBA featured a "tracking" auxiliary gain control that was gear-driven from the tuning mechanism and kept the gain level constant throughout the tuning range. The RBA was used by the Navy for about two decades after WWII ended and its superior performance illustrates what can be accomplished in TRF design when cost was not an issue - the RBAs sold to the Navy for $3000 a piece in the 1940s.

Now, all of the above isn't saying that a vintage superheterodyne can't do a good job on LW reception - I'm just saying the regen and TRF receivers can also do a great job on LF. The superhet, when specifically designed for LW, with low noise tubes and circuits, can perform quite well on LW when used with the proper antenna. However, many superhets just added a portion of a LW band to a receiver that was really designed for HF. These types of superhets are common and their LW performance is usually barely adequate. There are exceptions with the National HROs (using G, H and J coil sets,) the Hammarlund SP-200LX (aka BC-779) and the RCA AR-88LF (aka CR-91) being noteworthy as high performance superhets that do a great job on their limited coverage LW bands.

Many casual LW listeners aren't aware that all of the "top performing" LW receivers must be operated with some type of  low-noise antenna, even in a RFI-quiet location, to achieve DX reception on LW. In reality, most "high-end" LW receivers have about the same abilities and superior performance is more dependent on the operator's experience, the antenna type used and the receiving location rather than on the type of receiver being used. If the LW superhet user runs his receiver with a tuned loop antenna or a low-noise wire antenna like a Beverage, he will find the signal to noise ratio is greatly improved and, in a quiet location, he should be able to receive ample LW DX.

The Ultimate Vintage Long Wave Receiver? - If you're looking to find the ultimate vintage LW receiver,...the one that's the most sensitive,...the one that can pick up weak DX signals through any sort of noise,...the one that doesn't require special antennas,...well,...unfortunately that receiver doesn't exist. There are very good performers and there are "not so good" performers but there really isn't one receiver that "stands out" above the rest as the ultimate vintage LW receiver. I've tested and used dozens of different models of vintage LW receivers and in my opinion the "best" of these LW receivers all perform at about the same level. While all of the receivers profiled in this article can perform quite well on LW, there are some that standout as my "favorites" to use.

I have two "first" choices,... number 1-A, not unexpectedly, would be the Hammarlund SP-600VLF-31 receiver. It's an easy to use, easy to maintain, very sensitive LW receiver, although this high sensitivity also produces a fairly high noise floor almost mandating the use of a well-designed loop antenna. The SP-600VLF-31 is fairly expensive but the Dero versions seem to sell for much less (and they are SP-600VLF receivers.)

Number 1-B might be a surprise to many but it's a great performer - the British-built receiver RACAL RA-17C-12 with the RA-237-B Low Frequency Converter. Easily comparable to the SP-600VLF in its ability to pull weak signals out of the noise with the additional benefit of "to the kilocycle" dial accuracy. Like all of the "high-end" receivers, the RACAL RA-17 versions aren't cheap and then you must have the Low Frequency Converter which can be very difficult to find (and expensive.) A side benefit of the RACAL combo is its complete frequency coverage from 10kc up to 30mc. Both the SP-600VLF and the RACAL combo are the best performing vintage LW receivers I've used.

The next choice is the US Navy RBA receiver. The RBA is somewhat difficult to maintain (because of a very common problem with the Hammarlund ACX "hex collar" trimmer capacitors used in all of the RF Coils.) The RBA is large and heavy so it's somewhat difficult to set-up with its equally heavy, separate power supply and armored cable. But, once the RBA is working correctly it's a great receiver that's well-known for phenomenal sensitivity and dial accuracy. The Output Limiter circuit is one of the best.

My last pick of the "top" LW receivers would be the Collins R-389, that is,...when it's working correctly. It's a fantastic LW receiver and I would rate it as "one of the best LF performers" except it's a paragon of unreliability (due to complexity) that can be difficult to maintain or repair which seems to be a frequent task. The absolute worst problem is that many of the front-end replacement parts that might be required for a professional-quality repair are in the "unobtainium" category (after all, only 856 were built.) Add to that, Collins collectors have driven the price of the R-389 into the stratosphere - expensive beyond belief. Even "parts sets" are rarely found and if you do find one it will still be priced like it was a fully functional receiver. If you're willing to become a budget-challenged, electro-techno-mechanical-masochist, then the R-389 might be for you. Again,...when all is working correctly, the R-389 is a great receiver. The challenge is to get your R-389 operating correctly and to keep it functioning that way if you use it a lot (probably why most R-389s are Collins Collector's "shelf-queens.")

These four receivers are about the best of the vintage LW receivers because all four can detect very weak signals that are "in the noise." All four have direct frequency readout with illuminated dials, the RBA receivers have excellent Output Limiters that are very effective "static crash" noise limiters, the RACAL has a very low noise floor with high sensitivity and "to the kc dial accuracy." All four have excellent mechanical construction. However, even these top vintage LW receivers can't perform well within certain environments or when LW receiving conditions are poor.

Regardless of the LW receiver used, for effective LW DX reception you absolutely need the following:  First and MOST IMPORTANT is a good receiving location that has very low RFI-noise levels (Radio Frequency Interference, e.g., manmade RF noise.) High RFI-noise areas will limit what even the best receiver can pick-up and separate from the interference. In most densely populated urban areas, LW reception is virtually impossible due to the tremendous amount of interference from almost every electronic device in close proximity operating simultaneously not to mention all of the industrial electrical noise present 24-7. In these types of environments, a shielded-magnetic loop might help but don't expect to hear weak DX signals. At most, "blow-torch" Canadian NDBs or local NDBs are about all that can be expected when listening from an urban location.

Second, is a good low-noise antenna. An antenna that "picks up" a lot of RFI-noise will only compound a noisy location problem, making even the best LW receiver a poor performer. Even in RFI-quiet areas, using a low-noise antenna will benefit your reception. In rural areas using a large wire antenna becomes a possibility and what can be heard with this type of antenna is impressive. But, atmospheric noise will limit how often a large wire can be used.

When you have a superb receiver operating in a quite receiving location with a good low-noise antenna then you absolutely must to use headphones for the audio output. You should operate the 'phones directly from the 600Z ohm audio output of the receiver if possible. You'll never hear the extremely weak signals using a loudspeaker. 'Phones are a must. Always have the 'phone cups just in front of your ears to protect your hearing from static bursts. Avoid using rubber cups or padded cushions that surround the ears since this will have the phones in position to direct static bursts directly into the ear canal resulting in "ringing ears" or worst. Try to use "bare cups" or phones with small rubber cups with the cups in front of the ears (on your cheek bone.)

Finally, you must have good receiving conditions and that means you must do your LW listening during "the LW season." This would be late-Fall and Winter nights and early mornings (the "LW season" is usually between the Autumnal Equinox and the Vernal Equinox.) The following sub-articles in Part 4 detail some of these MW/LF reception problems and some of the solutions to noise and what types of antennas are best for successful LW reception.



LW RCVRs Part 1                     LW RCVRs Part 2                       Home-Index



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