Radio Boulevard
Western Historic Radio Museum

 

Vintage Longwave Receivers - Part 3


Profiling the Collins R-389/URR

 Profiling the Hammarlund SP-600VLF-31

Regenerative Receivers versus Superheterodyne Receivers on LW

Using Selective Level Meters as LW Receivers

Other LW Receivers

National HRO,  Hammarlund SP-200LX,  RCA CR-91
 

The Ultimate LW Receiver?



from: www.navy-radio.com
 

 

U.S. Army Signal Corps

Collins Radio Company

 

R-389/URR
 

 

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.

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. (Read update at the bottom of this section for problem encountered due to using the HP Function Generator.) 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.

Next tests will be with the remotely tuned loop on the Balanced Input and listening at night.  - April 24, 2018

Performance on Loop Antenna - I tested the remotely tuned loop antenna at 10PM in the evening so it would be fairly close to the conditions that were present when I tested the wire antenna. The loop was attached to the Balanced Antenna Input. I first tuned to 314kc for the local DGPS signal. It was strong and could be "peaked" with the loop's remote tuner. I proceeded to tune from 325kc up to 405kc. Only the very strong NDBs could be heard. BO 359kc and MOG 404kc. I tried the Unbalanced input with even less response. I switched back to the wire antenna but with it connected to the Balanced input. Signals were much stronger and all of the usual NDBs were tuned in. Signals from Oregon, Montana and Idaho were copied. Also WL 375kc in Williams Lake, BC, Canada.

Further testing will be required to determine why the Loop Antenna performance is not as expected. I did modify the Loop to perform best with the Hammarlund SP-600VLF. I may have to do further modifications to the Loop to attain best performance with the R-389.

Another possible explanation is the time of year. Late-April isn't the best time for MW or LF signals. Most of the time, I quit listening to this part of the spectrum by late-February because of much higher noise levels and low signal levels, even at night. -  April 24, 2018

Signal Generator Test - A quick test used the HP 606B directly connected to the Balanced Antenna input. I used a fully shielded coaxial cable to input the signal. I set the HP 606B to the 0.1v scale and set the meter to read 1.0. This signal read 100db+ on the CL meter at 200kc. I used the attenuator to lower the signal level in steps. At 1uv input the CL meter was just at the internal noise level and the signal was easily audible on loudspeaker. I repeated the test at 300kc and at 700kc with the same results. This isn't a true sensitivity test, it's just to see that the receiver does respond to very low level signals.

So, what I can say right now is that the R-389 seems to be performing well. It does better on a wire antenna on LW. On the AM-BC band signals are very strong and push the CL meter to nearly +80db. The USN MSK VLF stations also will move the CL meter to about +30db. A comparison test with the SP-600VLF might be an interesting experiment.  -  April 25, 2018

Comparison Test - I tuned in a few signals using the SP-600VLF using the wire antenna (during mid-day.) I could just barely hear MOG 404kc. DGPS 314kc was strong. WWVB 60kc strong and NLK 24.8kc and NPM 21.4kc were strong. I tuned in the same signals with the same antenna using the R-389. The results were nearly identical. The exception was I could easily hear the carrier of MOG but I could only hear the MCW signal a few times. My conclusion is that the R-389 performs just about like the SP-600VLF. See September Performance Update below.

Minor Problem Corrected - This R-389 had this unusual problem that when first powered up the received frequency was about 20kc low. The former owner told me at the time of purchase that the receiver would have to "warm up" and after several minutes it would jump to the correct frequency. I experienced exactly what he described in that after the receiver "warmed up" for twenty minutes, the tuned frequency would jump up 20kc and then everything was ready to use. This didn't seem normal but it wasn't too much of an issue since one usually allows a receiver to "warm up" anyway and it always took the same amount of time for the frequency jump to occur.

After all of the repairs and the alignment, I used the receiver for awhile. When installing a new Twin-ax to BNC adapter on the Balanced Antenna input, I happened to notice that the OVEN was turned ON. I checked the manual and read that the oven was only on the VFO and was designed to raise its internal temperature up to 167F - Wow! Anyway, I started testing the R-389 with the VFO oven off. The frequency "jump" never happened after I turned the OVEN off. I left the receiver turned on for hours and always the tuned frequency remained 20kc low.  >>>

>>>  In thinking about this problem, I knew that I hadn't synchronized the VFO as I always do on any R-390A that I align. On the R-389, at 15kc, the VFO output should be 470kc - exactly. I used a tube extension to access pin 5 of V702, the VFO buffer output tube. I used a digital frequency counter to measure the frequency exactly. It was 452kc at 15kc on the Frequency Dial. I had checked the mechanical limit-stops prior to this and those were okay. I assumed that in the past during an alignment someone skewed the VFO to correct the frequency readout with the VFO oven ON. I loosened the clamp on the VFO coupler behind the gear-driven mechanical limit-stops. This allowed me to just change the VFO only. I set the VFO for 470kc output with the frequency set to 15kc and tightened the clamp. I then checked the DGPS node at 314kc and it was at 313kc (BFO on) and I also checked local AM BC KOH 780kc and it was at 780kc with the 2kc bandwidth. A "touch-up" on the alignment was going to be required. Actually, the adjustments below about 150kc were pretty far out. The higher the frequency, the less the alignment was affected. More details in the next section below.

Is this "Oven Induced Frequency Change" a component that fails under heat? Or, is it a component the suddenly "gets better" with heat? With the instant nature of the change, I'd think the component fails with excessive heat. I'm just going to leave the VFO oven turned OFF and use the receiver. In hours of operation the VFO never gets as hot as when its oven is ON (167F - that's hot!)   May 10, 2018

Be sure to read the update for Jan 9, 2019 (below) for more info on this VFO problem.

A Different RF Signal Generator - I wasn't very confident that the HP Function Generator provided a very stable signal for alignment below 50kc. It seemed to be very erratic in both amplitude and frequency. The HP 606-B would only tune down to 50kc. I happened to look at my General Radio Type 1001-A RF Signal Generator and noticed that it would tune down to 5kc. It's a top-notch generator dating from about two decades before the HP 606B. I had tested and serviced it a few years ago so it still was operating quite well. I decided to use the GR generator for the next alignment which was after the VFO had been synchronized as mentioned in the section above. The signal from the GR 1001-A was super stable both in amplitude and frequency. I found that the alignment I had done using the Function Generator was off by quite a lot. It's important to remember that adjusting the slugs doesn't affect the accuracy of the frequency readout. That's a function of the VFO and the 10.445mc Crystal Oscillator. You have to set the receiver frequency as specified and then "rock" the signal generator frequency and set it to the "peak" output as measured at the Diode Load. Then adjust the slugs for that band at that frequency. Do the same for adjusting the trimmers for the top end of the same band. Most of the errors in adjustment were below 150kc. Above 150kc there was very little error. The end result is much more gain in signals below 150kc and especially below 50kc.     May 13, 2018 PERFORMANCE UPDATE:  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: VFO Problem - January 9, 2019 - This problem started out with just a defective tube in the IF module but seemed to evolve into a major issue. The initial bad tube was the second IF amplifier that had an open heater. Besides the second IF tube, three other tubes then don't have heater voltage since these tubes are connected in series-parallel. I went ahead and tested all of the tubes since it had been about nine months since the last complete test. I found about four more weak tubes - not bad but reading about half of minimum acceptable (I was using the TV-2 tester this time which is more critical in its testing results.) The receiver was then working fine on the bench. Then I installed it back into the CY-979A cabinet and had planned on listening that evening. The evening session turned up another problem. The VFO was now causing the received frequency to be 40kc lower than the frequency readout (at 700kc.) Since the VFO was way off frequency, the rest of the receiver front end was essentially not in alignment so no signals were heard on MW. On the AM BC, strong stations could be heard but they were 40kc lower than they should be. This was the problem I had been having when the VFO oven was turned on. Now it was happening at ambient temperature except there was no "frequency jump" after a "warm-up" as before. I could "tap" on the side of the VFO and the frequency would sometimes jump the 40kc other times it wouldn't. It seemed that something mechanical had happened inside the VFO.

Pulling the VFO, removing the outer cover and oven, then the inner cover provided access to the VFO circuit. At first everything looked normal except that it was obvious that the VFO had been opened before and the desiccant packets removed. Closer examination with magnification showed that the rotor of the the trimmer capacitor was covered with white oxidation. Most of the metal parts inside the VFO had some contamination from this white powder. The oxidation seemed to brush off easily using a small stiff paint brush. I thoroughly cleaned the trimmer capacitor including cleaning both sides of each individual plate of the rotor and stator using a thick paper pulled thru the gap of the plates. All solder joints were checked.  >>>

>>>  After a complete cleaning, I reassembled the VFO and installed it into the receiver. Upon power up, the tuned frequency was about 40kc off. I left the receiver turned on for a couple hours and no changes occurred. I then resynchronized the VFO (470kc out at 15kc) and performance was pretty much back to normal.

I suspect that the corrosion was "growing" on the plates of the trimmer capacitor and intermittently contacting an adjacent plate (or plates.) The semiconductive nature of the oxidation may have caused a slight capacitance change rather than a short. The heat would cause expansion to increase the clearance enough to eliminate the "contacting" condition. The receiver was originally calibrated for this "non-contacting" condition. When I turned the oven off, the frequency "jump" didn't happen but probably the expansion was going to take much longer to occur so I thought that the problem was solved. The result was that I had calibrated the VFO for the "contacting" condition. For nine months the receiver operated fine and I didn't experience any change in calibration until the IF tube failure and subsequent repair effort. I think the physical movement of removing and installing the receiver into the CY-979 cabinet may have contributed to VFO issue showing up at this time.

Cleaning the oxidation in the VFO seems to have cleared up the problem. Since the "contacting" condition is hopefully gone for good, I had to recalibrate the VFO to the new, hopefully permanent, "non-contacting" condition. 

UPDATE: January 15, 2019 - The frequency "jump" is back but only 20kc this time. Pulled the R-389 out of the cabinet and turned it on its side. Gentle tapping on the VFO made the frequency jump back 20kc. More tapping didn't change the frequency. Have powered the R-389 several times over several days with no change in VFO operation. Seems mechanical. Disassembly of VFO will be necessary again for better cleaning and resolder all joints,...  

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.)
 

 

Hammarlund Manufacturing Company, Inc.

 

 

SP-600VLF-31

 
 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 may have just been thinking of an 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 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.


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 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. 

It's worth noting that, in 2014, I haven't been able to reliably receive Radio Rossii 279kc from Sakhalin Island due to a digital-data beacon also 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 shutdown Jan. 9, 2014)

Although NDBs are MCW signals, all "NDB-chasers" use a BFO (tuned to the exact 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.) 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 will probably 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 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 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.

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


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 tuned loop of some kind. In RF-quiet areas, various types of wire antennas can be used,...sometimes,...depending on receiving conditions.

SP-600VLF-31 UPDATE: Nov 2014 - Using the Remote Tuned Loop Antenna - I decided to try the six foot remote-tuned loop antenna with the SP-600VLF-31 receiver. The loop suffered a bit during the move down here to Dayton. I had it stored in one the shop garages. I brought the loop out for inspection and found that the wire had come out of the grooves in the combs in several places and there was wire hanging and getting tangled. All that was needed was to straighten out the wire and get it back into the grooves of the combs to get everything looking okay again. During the move I discarded the loop's stand because it was beginning to fall apart. So now I'm without a stand for the antenna but it can set on one of its corners and be propped up against the wall - at least for testing. A new 9vdc battery was installed to get the bias and remote tuning working again.

With the tuned loop upstairs and propped up so it was pointing sort of north-south, I tuned in FCH 342kc and peaked the signal using the remote tuner. What I noticed was the gain peak was not as pronounced as it seemed to be with other receivers. Still, there was a peak, so I figured the loop was working. I waited until dark and then positioned the loop east-west. In tuning from around 325kc up to 400kc several NDBs from the US mid-west were received and several Canadian NDBs from Manitoba and Ontario were also received. The improvement over the "ham antenna" with the feed line shorted was dramatic. The only thing noticed was the "peak tuning" of the loop is very broad and not all that much gain change is noticed. I suspect that there may be an impedance mismatch between the loop and the SP-600VLF-31 that will require a little more tweaking. But, for now, I have a nice improvement in signals and some directivity. - November 15, 2014         Removing one turn on the pick-up loop, which had three turns and is now two turns, has improved the loop performance with the 600VLF. Sharper tuning (higher Q) and seems to have better gain. - November 17, 2014        

NOTE: As of JAN 31, 2015 - 23 "newly heard" NDBs with the SP-600VLF so far with well-over 200 NDBs logged. Also, the Hawaiian LLD 353kc has been copied more than once - a distance of over 2500miles. The recommended "arrow" placement (position 5) of the Crystal Filter isn't particularly good for NBDs. I find that around position 8 gives better noise reduction and allows weaker signal copy. Once in a while, adjusting to 2 or 3 will increase the bandwidth and the "highs" and sometimes this helps with multiple signals on the same frequency.   
Feb 4, 2015 -
Newly heard NDB is another Hawaiian NDB, POA 332kc copied at 0550PST.

Modified the loop again, October 2018 - This time the pickup loop was increased to four turns and it was moved to three inches away from the tuned loop. More gain with the four turns and better selectivity with the increased distance between the pickup and the tuned loop. Trying for better performance on 630M.

UPDATE: 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 loop now that I've modified the pickup loop. I did have a successful two-way QSO with NO3M on December 7th.

 

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. >>>


photo above:
   1923 RMCA  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 has gone "off the air" 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.)

Mentioned above, the RCA-built USN RAA longwave superheterodyne receiver was a gigantic, 465 pound receiver that used 14 tubes and had four different IFs that were individually selected by the bandswitch(s.) Four specifically tuned BFOs were also needed in the RAA. The four different IFs allowed for uninterrupted coverage from 10kc to 1000kc. The complexity and expense of the RAA forced the Navy to reconsider earlier, less complicated and less expensive longwave receivers. After the RAA, all Navy longwave receivers were either TRF with regenerative detector or TRF with tracking BFO. Of the latter catagory is 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. When specifically designed for LW, with low noise tubes and circuits, a superhet 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 rather poor. 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 fine job on their limited coverage LW bands.

Also, there are two well-known, vintage, ultra high-end, designed specifically for LW, receivers that were made for the military and for the laboratory. The Hammarlund SP-600VLF is a top performer with continuous coverage from 10kc up to 540kc and the familiar "SP-600" appearance. However, it isn't just an SP-600 with LW coils installed in the turret but rather it's a completely "designed for LW" receiver that uses the basic SP-600 physical appearance and mechanical features. Unfortunately, the "VLF" is a rather rare and usually expensive version of the SP-600 and, while the SP-600VLF is an exceptional performer, it does require a low-noise antenna and, for LW DX reception, it's really helps to have a low-noise location. The other "high-end" LW receiver is the Collins R-389 LW receiver but it's so rare (856 built) and so expensive that it has become better known as an ultimate "Collins Collector's receiver" than known for its incredible LW performance. The R-389 is a mechanically and electronically complex, double conversion receiver that mixes the incoming RF LF frequency with a VFO plus crystal oscillator to convert the frequency to an IF of 10mc which is then mixed with the same crystal oscillator to achieve the 455kc IF (similar to the Wadley Loop.) This signal is then routed thru six IF stages using the same type of IF module used in the R-390 receiver. The remaining circuits and modules are the same as the R-390 receiver. The R-389 is another exceptional receiver but many times, its performance is reported as "adequate but not phenomenal." It's likely that many of the R-389 receivers in collections would benefit from a complete servicing since these complex receivers generally don't attain their high-performance capability unless they are well-maintained and expertly aligned by competent techs using laboratory quality test gear. As with any LF receiver, a low-noise location is necessary for LW DX reception.

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.

 

Selective Level Meters and Wave Analyzers as Longwave Receivers

Selective Level Meters and Wave Analyzers are test instruments that incorporate a tunable sensitive receiver with selectable filters and attenuators to drive a calibrated analog meter. These instruments are used for a variety of purposes such as measuring leakage or unwanted signal levels on transmission lines, testing response of various kinds of amplifiers, some types even provide a built-in signal generator for test signals. None of these type of instruments are designed specifically as Longwave receivers, however, some of them actually perform quite well in that function. I have used two Selective Level Meters as LW receivers, a Sierra Model 125B and a model made by Cushman. The Sierra 125B was a vacuum tube model and was fully operational with a good set of tubes and I had performed a full alignment. However, that particular model did not have a BFO to help locate weak NDBs. This made the Sierra 125B very limited in its usefulness as a LW receiver. I also had loan of another selective level meter made by Cushman. This 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. The set's owner was also disappointed with the Cushman's performance as a LW receiver and he eventually sold it on eBay. By far, the best instruments for use as longwave receivers are some of the Hewlett-Packard Wave Analyzers.

I happen to have the HP 310-A version in which the receiver tunes from 1kc up to 1500kc. The 310-A 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 instrument with a mechanical counter providing the digital frequency readout.

photo left: The Hewlett-Packard 310-A Wave Analyzer. 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 tags above the meter switch are USAF property identification tags.

 

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 is a severe limitation for using it as a LW receiver

I find that the performance of the HP 310-A is very favorably compared with any of the vintage longwave receivers profiled in this web-article. 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, especially when using a tuned loop antenna. Watch the meter and keep the measured signal level at about 75% to 95% of FS with the Relative Gain control. 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. My conclusion is that Selective Level Meters and Wave Analyzers are designed for finding and measuring leakage in systems, measuring frequency response or measuring unwanted signals on transmission lines and other similar applications. Some of these instruments are useless as longwave receivers. Read up on any instrument you intend to purchase for longwave reception and make sure others have had success using it for that purpose. The first two instruments I tried were of the "useless" variety, however the HP 310-A performs very well as a longwave 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" radios for the home tuned down to 150kc because there was so much to listen to then in that part of the spectrum at that time. 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.) 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" receivers. Photo shows the SP-200LX version. IF is 465kc on all versions and double preselection is used on all bands. There was also a SP-100LX version that is an earlier version (1937-38) with the same frequency coverage but this version is rare.

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


Covers 550kc to 73kc (550kc to125kc 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 generally 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. IF is 735kc on all LF versions and double preselection is used on all bands.

 
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 kinds of vintage LW receivers and in my opinion the "best" of these types of LW receivers all perform at about the same level. While all of the receivers profiled in the first section of this article can perform quite well on LW, there are a few that standout as my "favorites" to use. My first choice overall would be the Hammarlund SP-600VLF-31 receiver. It's an easy to use, easy to maintain, sensitive LW receiver. An extremely close "second" is the US Navy RBA receiver. The RBA is somewhat difficult to maintain and difficult to set-up because of the separate power supply and armored cable but its sensitivity is phenomenal. My third pick would be the somewhat rare Collins R-389. It's a fantastic LW receiver and I would rate it as "the best LF performer" except it's a paragon of difficulty to maintain and expensive beyond belief. These three receivers are about the best of the vintage LW receivers because all three can detect very weak signals that are "in the noise." All three have direct frequency readout with illuminated dials, the RBA receivers have excellent Output Limiters that are very effective noise limiters and all three have excellent mechanical construction. However, even these three 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. Second, 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. 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. Don't use the 'phones jack as the audio source. You must operate the 'phones directly from the 600Z ohm audio output of the receiver. 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. Never use 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. Always use "bare cups" with the cups in front of the ears. Finally, you must have good receiving conditions and that means you 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.

CONTINUE TO PART 4

 

LW RCVRs Part 1                     LW RCVRs Part 2                       Home-Index

 

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