Radio Boulevard
Western Historic Radio Museum

RCA's Amazing AR-88 Series of Receivers

Part 4

Collector's Gallery of AR-88 Photos
Operating AR-88s in Diversity
Performance Compared to Other Receivers
AR-88 Performance Today
Non-invasive Muting Mod
Using the CR-91 on Long Wave
References

WS-430 - Chi-Comm Copy of the AR-88

Collector's Gallery of AR-88 Series Receivers

W3TA - AR-88D

 with Smooth Finish Semi-gloss Black Panel with Engraved Nomenclature

Tom W3TA owns this early AR-88D SN:005112 that has the smooth finish semi-gloss black panel with engraved nomenclature. All of the early AR-88 receivers used this type of front panel. The very earliest receivers also had a solid-yellow tuning dial (not alternating black and yellow scales.) Nearly all of these early versions of the AR-88 were exported to England using Lend-Lease. This receiver either was sent and somehow came back (not many did,) or, it was never shipped overseas in the first place. Also, of note,...this receiver has the RCA Carrier Level meter installed. Original RCA meter installations on WWII AR-88s were seldom produced due to a shortage of meters during WWII. It's thought that during the post-WWII period, RCA offered a kit that provided AR-88 users with the correct meter and components along with instructions for proper installation.

NOTE: Take a look at the cover of the WWII AR-88 brochure shown in Part 1. Note that the artwork shows the smooth finish front panel with the receiver installed in wrinkle-finish cabinet.

WS-430 & WS-430II - Chinese PRC Version of CR-88A/SC-88

In the mid-1950s, the Chinese started building copies of the RCA CR-88A (and possibly the SC-88.) These receivers were designated as WS-430 and while they are very close copies, they are not what one could call replicas. Instead the Chinese used Russian tubes, slightly changed the locations of some of the components and ultimately replaced some of the tubes with miniature versions. These later copies were designated as the WS-430II. These receivers were used in airports and other communications locations in China. Note in the photograph that this receiver is equipped with a Diversity IF Gain control which implies that this receiver may have been used in a diversity system. With the top of the chassis mounted crystal for the Crystal Filter and the Diversity IF Gain control it is possible that the SC-88 was copied.

Today, the WS-430 series doesn't seem to be very popular with Chinese hams or collectors although this one was pictured on a website of Chinese equipment. Apparently, most Chinese hams prefer new, modern equipment and are not fans of receivers that were copies of USA designs.

Thanks to WA6OPE and WB6NVH for the WS-430 info.

ZS6JPS - CR-88A

This nice condition CR-88A is located in South Africa and is owned by Jacques Scholtz, ZS6JPS. The receiver's serial number is 001700. It has an original, RCA umber '88 series cabinet although the two screw covers are missing. CR-88A receivers were typically for triple diversity receivers but many were sold as "stand alone" receivers by RCA. The CR-88A is the post-WWII replacement for the AR-88F.

K5UJ  -  CR-88

This very nice CR-88 is owned by K5UJ, Robert Akinson. It was purchased at a Ft. Wayne, IN hamfest last November. The receiver had been fully rebuilt and also featured the "hard to find" Carrier Level meter (all CR-88 receivers were originally equipped with CL meters but sometimes they've been removed for some reason.) Robert uses the CR-88 with a pair of 8 Z ohm 12" speakers in cabinets and also utilizes a TR switch with the receiver when paired with a transmitter. This CR-88 is sn 1695.    NOTE: Color is way off in this photo. See the W7MS CR-88 below for an accurate front panel color representation.

W7MS - CR-88 sn: 001341

Mike just finished his restoration of CR-88 sn 001341 recently. The receiver has had all of the tub caps replaced and the Micamold caps were also replaced. All out-of-tolerance resistors were replaced. Mike also sweep-aligned the CR-88 for attaining the best audio response from the receiver. Note that this CR-88 has the original carrier level meter.

Mike came up with an easy non-destructive way to mute the receiver. All CR-88 receiver panels are punched for the Diversity IF Gain control but have a snap-hole-plug installed instead. Mike removed the snap-plug and installed a two position rotary switch with RCA knob. The switch has the RF Gain control ground return routed to one terminal and ground on the other terminal thus providing a front panel mute function. By switching to the "non grounded" position (or "mute") the RF Gain pot is then not going thru the 6.8K resistor to ground so the RF gain line goes to the high side of the bias supply which simulates turning the RF Gain maximum CCW. Mike also mentioned that a line from the gain control side of the switch could be run to the AVC terminal (with the AVC wire unsoldered and its end insulated with shrink tubing) on the rear of the chassis thus providing a remote mute function. So, either local or remote muting is provided with non-destructive mods. A really easy solution to the common problem on all of the '88 receivers and their lack of a remote standby that doesn't involve the soaring B+ when TRANS is used. More details on these remote muting mods below in "Using the AR-88 as a Ham Station Receiver."

W3TA - CR-88  sn: 001262

This is an unusual CR-88 the was retro-fitted with much more durable stainless steel nomenclature tags and one large nomenclature plate. The panel is fine wrinkle finish in a light greenish-gray color. The standard color would have been RCA Umber and the use of a wrinkle finish type of paint would seem to indicate an end-user paint job. Obviously, the refinish work was professional-level and the solution to the nomenclature problem was accomplished using stainless steel tags that were engraved using a pantograph machine and then filled with black paint. The end result is quite professional in appearance. It's suspected that this receiver was either a special order for maritime use or, more likely, it was rebuilt for marine duty by a professional marine-radio rebuilding business. The CL meter was standard for the CR-88.

N1QCR - CR-91A  sn: C385

This unusual CR-91A is owned by Chris N1QCR. Chris found the receiver at a swap meet where it was offered in "as is" conditions - dirt and all. After a clean-up, the CR-91A was found to in very complete condition, including all of the alignment tools (located under the RF Cover.)

What is unusual about Chris' CR-91A is that it was "reconditioned" by a private electronics firm in Canada, "Canadian Aviation Electronics LTD" with a date on the tag of FEB/5/1953. Obvious in the photograph are the white dials and meter scale. RCA-Montreal apparently supplied some CR-91A receivers equipped with white dials to certain end users (RCAF?) The metal tag on the front panel is the standard RCA-Victor Montreal data plate.

Chris is planning to fully restore the electronics of the unique CR-91A and incorporate it into a relay rack for use with a vintage transmitter.

NOTE: The Carrier Level meter is correctly showing FS with power off. The original '88 meters are FS mechanical zero

Additional NOTE: It appears that some CR-91A receivers equipped with white dials were supplied by RCA-Montreal to certain end users. The second CR-91A "white dial" receiver is a RCAF receiver with the SN: C241M.

N6YW - CR-88B

The last version of the RCA '88s, the CR-88B. Few were built and today it is an extremely rare receiver. Condition doesn't get much better than this example owned by William Yates, N6YW. Billy also has the original matching loudspeaker for this rare receiver.

Operating Multiple AR-88 Receivers in Diversity

Let's take antennas first. The DR-89/RDM manuals state that the required antenna spacing is 1000 feet oriented in a triangle. However, this was military/commercial set-ups and provided absolutely the best diversity effect for nearly all frequencies in the MF and HF part of the spectrum. Usable diversity effect can be achieved with antenna spacing at around one wavelength at the received frequency, sometimes even less. If space is really tight, one antenna can be a vertical and the other a dipole, in other words, one vertically polarized and one horizontally polarized antenna - assuming dual diversity. For most frequencies in the HF region, 100 feet of separation will give usable diversity effect most of the time. It's a little close for 80 meters so if you can get greater spacing then try for at least one wavelength.

Next are the particular AR-88 receivers that you are going to use. Your AR-88 receivers should be the actual diversity models that were used in the DR-89, RDM or OA-58A/FRC receivers. That way you'll have the separated Diode Load and Diode Return lines and you'll have the AVC line available. Additionally, only the diversity receivers have several resistor changes in the IF section for better diversity effect. Although all AR-88 versions provide a terminal to access the AVC line, only the true diversity versions will provide terminals to allow "diode-OR'ing" of the second detectors of each receiver to achieve true diversity operation.

When receivers designed for diversity operation are used, you'll find that the second detector output is brought out to terminals on the rear of the receiver marked "Diode Load" and Diode Return." When operating two or more receivers in diversity, each of the receiver's detector outputs, the Diode Load, are connected together, in other words, "diode-OR'd." This then allows the receiver with the strongest signal to dominate the other receivers. As the signals fade because of multipath phase shifting on any of the antennas, whichever receiver has the strongest signal will dominate the Diode Load line. The Diode Return line was provided to route the signal on to the receiver's audio output circuits. Only one receiver needs to provide audio output for the diversity system. The remaining receiver's audio circuits are generally left not connected to the Diode Return. 

In order to keep the diversity system stable it is necessary to have feedback for control and this is accomplished with the AVC line. All AR-88 versions of the receivers will provide an output for the AVC line at the rear of the receiver. For diversity operation, all of the receiver's AVC line terminals need to be connected together.    >>>

Now in the original DR-89 diversity rack, the operator had the Monitoring Unit where each receiver's Diode Load current could be actually measured. However, most amateurs don't have all the pieces to the diversity rack. An elaborate set-up could use three current meters (0-300uA) in the Diode Load to Diode Return line to act as a more accurate reference for balancing. In the professional set-ups, much of the copy was done by machines that required absolutely perfect signals but since our use is only for listening pleasure, balancing by ear is certainly close enough. As the receivers become equal in response (balanced,) the diversity signal will become more stable and fading will disappear.

Dual diversity with properly spaced antennas will reduce fading about 90% while triple diversity with properly spaced antennas will reduce fading by 99%.

Comparisons with the AR-88's Contemporaries

SP-200SX - 1940

HRO Senior - 1940

SX-28 - 1940

The AR-88 Performance Today

The AR-88 series receivers are examples of 1940s receiver designs that will perform so well you'll think it was designed in the 1950s or 1960s. They were actively used by RCA and RMCA up into the 1970s when most 1940 radio designs had long since retired. Highly sensitive all the way up to 10 meters with five steps of selectivity to cope with crowded bands, an effective noise limiter and, of course, that fabulous audio that reproduces those low bass tones with no distortion.

The AR-88 high frequency sensitivity is renown and was achieved by using polystyrene coil forms in the higher frequency bands - and this in a day when most people had never heard of polystyrene plastic. Full sensitivity is available all the way up to 10 meters. Hearing stations was really never a problem with the AR-88. Selectivity is a little problematic because the early AR-88 design assumed that all you wanted the Crystal Filter for was to narrow the IF passband. It does that very well but, as many AM ham ops know, a good crystal filter can also be used to eliminate heterodynes. CW ops know that a good Crystal Filter can enhance certain audio tones making CW easy to copy through QRM and QRN. RCA decided to change the AR-88 design after WWII and moved the Phasing Control to the front panel. If you want to have the advantage of a Crystal Filter Phasing control easily accessible on the front panel, you'll have to find the CR-88 version or other late versions of the receiver.

Dial accuracy is where almost all vintage receivers find their detractors and the AR-88 is no exception. The tuning dial is "1940s" accurate but since wide slices of the spectrum are covered in each band, the resolution of the dial is necessarily vague. The ability to have 1.0kc readout (or better) on a receiver has been around since the late 1940s but many of today's hams have never been exposed to how frequency accuracy was achieved without a Collins-type readout (or, a modern digital readout.) Before the digital world, every commercial and military station had heterodyne frequency meters and if it became necessary to know exactly where the receiver was tuned, these instruments allowed the operator to set the receiver frequency to better than 1.0kc accuracy. The extreme scaling of the logging dial (4400 divisions) then allowed the operator to return to that exact frequency once the relationship of tuned frequency to logging dial reading was known.

SSB signals are easy to copy on the AR-88 and you don't need to do any modifications either. Simply turn off the AVC, increase the AF gain to near maximum and then reduce the RF gain by about 25%. Tune in an SSB signal with the receiver in REC CW (BFO on) until the voice sounds normal but overdriven. Then slowly reduce the RF gain until the audio clears up. Usually, the RF gain is about 60% or so on most SSB signals but it depends on signal level and the band in use.   

Since a VT-150 tube regulates the +150vdc voltage (which is used for the LO and BFO plates besides the receiver screen supply) the AR-88 is very stable. Drift is practically non-existent after about a 10 minute warm-up. You can listen to the West Coast 40M SSB Swap Net (or your local Amateur HF SSB Swap Net) without getting up to retune every five minutes. For CW, the stability makes this mode easy to enjoy when using the AR-88 as the receiver.   >>> 

The antenna connections are originally terminal strips but it is easy to utilize coax as the feed line by connecting the shield to the ground-A2 terminals and the center conductor to A1. Spade lugs can be crimped or soldered to the coax shield and center conductor for easy connection to the terminals. This provides an unbalanced input to the AR-88 which is the normal output from a standard antenna coupler that would be used with a typical ham antenna. The type of antenna used with the receiver will determine its level of performance. A matched resonant or tuned antenna will give the best results on the lower frequencies and a gain antenna like a yagi or quad will give excellent results on the highest frequencies. Using random length, untuned end fed wires will result in very limited performance potential for the receiver.

Using the correct impedance loud speaker will provide very loud audio output from the 2.5 ohm Z terminals. The original speaker is hard to find but any speaker from 3.2 to 4.0 ohms Z will provide very loud audio output and can reproduce significant bass. Speakers with 8 ohms nominal impedance require that the AF gain be advanced substantially. Try to use the lower Z speakers for best audio performance. The AR-88 AF gain control is normally advanced about 20% to 30% for normal listening when in the AVC-controlled AM mode and driving the correct speaker impedance. You can also utilize the 600 ohm Z "line" audio output with a matching transformer but I have always found the 600 ohm Z audio to not be quite as clear sounding as the 2.5 ohms Z output. If you do use the 600 ohm line for the audio output be sure to install a 4.7 ohm 2W resistor on the 2.5 ohm Z output terminals for a load.

Using a good quality, 3.2 ohm Z speaker will provide excellent audio but don't be fooled into thinking that a modern 4 or 8 ohm Z stereo speaker box will sound really great - they usually don't. The reason is they aren't very efficient with only 2.5 watts of drive power available from the AR-88. The old style, fairly stiff suspension, 12" PM 4 ohm Z speaker mounted in a large box with bass reflex port will sound best. If you can find a large speaker with a 3.2 ohm Z voice coil, the performance will be even better since you won't have the AF gain quite so advanced as with the higher Z speakers (for some reason, 12" speakers with 3.2Z VC seem to be hard to find.) The original MI-8303D speaker is only an 8" speaker but it is very good for communications-type audio. The larger speakers with good enclosures will show-off the AR-88 audio best but it does depend on what you're listening to. AM-BC or SW-BC will offer the best demonstration audio. One last note on audio,...if you're doing CW you don't want a lot of bass so use to HF TONE control to enhance the higher tones and that makes CW much easier to copy.

Then there's the weight issue. There's no doubt that the AR-88 is a very heavy receiver. In the cabinet, with all of the shields installed, it will weigh just slightly over 100 pounds. This makes moving the receiver around a strenuous effort. I find that it's very helpful to remove the receiver from the cabinet when moving. If the bottom cover is installed, it should also be dismounted. This will lighten the load by around 20 to 25 pounds. I've found that AR-88 chassis alone weighs less than 75 pounds. If the bottom shield is removed, the weight goes down to about 70 pounds. I don't know where the idea that the "bare" rack-mount receiver weighs 100 pounds came from - it doesn't. But still, the use of a roll cart is a tremendous help when moving the receiver from the work bench to another room - like the ham shack.

Finally, remote standby was never incorporated into the AR-88 series because of its primary function as a surveillance receiver. There's also quite a bit of negative history reported if TRANS is used actively for a panel-type of standby switch. Use of an electronic TR switch also has its own disadvantages unless CW is your only mode employed. If an actual T-R relay is used and it provides isolation to the receiver during transmit then the RF gain can be turned down to avoid audio feedback in the Voice mode. Separate transmit and receive antennas can also be used but still the receiver needs to be muted if the mode of transmission is Voice (AM.) The following section, "An Easy and Reversible Muting Mod for the AR-88 Receivers" provides the details on incorporating a very easy to install mod that doesn't do any damage and is easy to remove if desired. It provides a method to remotely mute the AR-88 while in the transmitting mode.

An Easy and Reversible Muting Mod for the AR-88 Receivers

Utilizing the AR-88 receiver or one of its variants in a ham station will require some serious thought on how to accomplish receiver "stand-by." This is because all versions of the receiver are designed to not use the station transmitter to actuate a remote standby condition in the receiver. If your AR-88 is a "stand-alone" version with the "TRANS RELAY" terminals, you'll find that RCA designed the receiver to provide the Send-Receive function (closure of switch contacts) with the operation of the function switch to the "TRANS" position. This function was meant to operate the station Send-Receive relay but, of course, having the receiver control the Send-Receive function is opposite of the normal ham station operation. While you could have the "TRANS" position operate a transmitter's remote push-to-talk line with the receiver, not all transmitters provide a remote PTT line.  

If your AR-88 is a Diversity receiver, you won't even have the "TRANS RELAY" terminals (although some early diversity receivers do have the two wires included in the harness.)  >>>

If you operate CW only, then the easiest solution is to use an electronic T-R switch to protect the receiver's input. These devices were originally developed for "break-in" keying which actually allowed you to keep the receiver operating while you were transmitting CW. You could actually hear some signals in between your sending (unless you sent fast CW in which case you had to pause between sentences for "break-in" stations.) The electronic T-R switch can be used on AM but it has so many disadvantages that most of the potential users become frustrated with the incessant feedback and end up using the "TRANS" position for full muting. The following simple modification will provide the AM operator an easy and reversible way to remotely mute his AR-88 receiver.

So, if you have a standard receiver, e.g. AR-88D, AR-88LF, CR-91 or CR-88, this mod will be incorporated using the AVC terminal. If you have the diversity versions, e.g. AR-88F, CR-88A or SC-88, this mod will be incorporated on the DIODE LOAD/DIODE RETURN terminals.

What the mod is going to do is to relocate the RF Gain control ground-side terminal to either the rear AVC terminal or to the DIODE LOAD/DIODE RETURN terminals. Since the RF Gain controls the bias voltage, if we remove the ground connection at the potentiometer, the RF Gain bias will go to maximum negative voltage thus simulating turning the RF Gain all the way down. The RF Gain control chassis ground connection is through a 6.8K ohm resistor that can actually be any value from 5.6K to 6.8K depending on which model AR-88 you have. The 6.8K resistor prevents taking the bias voltage directly to chassis ground if the RF gain control was at maximum gain (minimum resistance.) When disconnected from chassis for muting, it doesn't matter where in the circuit the 6.8K resistor is BUT for receiving the 6.8K resistor must be between the RF Gain pot and chassis. It will be noted that the AVC terminal mod disconnects the 6.8K from chassis while the DIODE LOAD/DIODE RETURN mod disconnects the pot from the 6.8K resistor that always has one end connected to chassis. Both connections function identically for muting.    >>>

Using the DIODE LOAD/DIODE RETURN Terminals (AR-88F, CR-88A or SC-88) - Remove the 6.8K resistor from the RF Gain pot and chassis. Unsolder the DIODE LOAD and DIODE RETURN wires from the rear terminal strip and solder these two wires together. Use shrink tubing to cover the solder joint. Now install a solder lug under the nut that mounts the terminal strip. Solder the 6.8K resistor from the DIODE RETURN terminal to the solder lug. Next solder an 24" long wire to the DIODE LOAD terminal. Route the other end of the wire along the wiring harness up the center of the chassis to the front panel. Trim the length of the wire as needed. Solder the end of this wire to the RF Gain pot terminal where the 6.8K resistor was connected. This completes the mute mod. You can now remotely short the DIODE LOAD and DIODE RETURN terminals for normal operation of the RF Gain control or remotely open these terminals for muting.

Remote Mute Cable - Since the muting line is essentially an extension of the RF Gain control that will be "floating" when the receiver is muted, it is necessary (when a transmitted RF signal is present) to use a two-conductor, shielded cable for the external connections from the receiver to the auxiliary contacts on the T-R relay. The shield of the cable can be connected to the chassis of the receiver using the antenna ground terminal which is easily accessed. At the relay end, the shield should be connected to the relay body. There are several screws available for a ground connection on most relay bodies (the Dow-Key, for example.) Keep the length of cable as short as possible by mounting the T-R relay nearest to the receiver.

NOTE:  The basis for this simple mod came from W7MS. Be sure to take a look at "Collector's Gallery" above and specifically the W7MS CR-88 receiver. Mike added a rotary switch in the IF Gain pot hole that provides an easy way to "mute" the receiver either locally (from the front panel) or remotely (repurposing the AVC terminal on the rear chassis.) Thanks to Mike for this really useful, non-invasive and easily reversible mod.

UPDATE: I've installed this muting mod on my CR-88A receiver using the DIODE LOAD and DIODE RETURN terminals as described above. I have the CR-88A set up with a Collins 32V-2 transmitter running just over 100 watts output. I'm using the auxiliary contacts on a Dow-Key T-R relay with shielded cable (about two feet long - probably longer than necessary) from the receiver to the transmitter. Operation on AM is a real pleasure now. No more manually switching to the TRANS position for standby and no more feedback when I forget to switch. This easy to install (and non-destructive) muting mod has made the CR-88A really enjoyable to use as the station receiver. One note, if you turn up the receiver Audio Gain to maximum you will slightly hear the audio modulation of your transmission but it's far below a level that causes feedback. At normal listening levels (Audio Gain about 25%advanced) nothing will be heard in the loudspeaker when the receiver is muted.

CR-91 SN 050068 with MI-8303D Speaker
note that the CR-91 has "PHONE" and "BFO" indicated on front panel function switch nomenclature rather than "REC MOD" and "REC CW" - this photo was taken in April of 2010.

Using the CR-91 on Longwave - 2010
 

The AR-88LF and the CR-91 receivers will tune from 70kc up to 550kc on Bands 1 and 2 allowing the user to tune in the thousands of Non-directional Beacons, NDBs, around the world. NDBs transmit in both the LF and MF part of the spectrum and are found from 195kc up to 525kc. Each NDB is assigned a two or three letter identification that is sent in MCW (Modulated CW) every few seconds. The transmitter antenna is usually located very near the airport runway since these were a primary navigation signal at one time. Most airport NDBs run 25 watts while regional beacons may run up to several hundred watts. Transoceanic beacons may run as much as 2000 watts. The modulated signal uses a 400 hertz tone and the CW is sent at a rather slow speed, usually about 10 words per minute (or less.) During the daylight hours only local NDBs will be received. Regional NDBs can sometimes be received as far as several hundred miles during the day, depending on the time of year. Nighttime listening is by far the most fun as NDBs can be received from thousands of miles away. Even 25 watt NDBs can be received at great distances when using good equipment and a proper antenna.
 

Finding the CR-91 in Reno in 2009 - I was lucky enough to have purchased CR-91 SN 050068 from Reno's only surplus store, Twin City Surplus, in late-2009 (unfortunately, after decades of supplying the surplus needs for Northern Nevadans, Twin City Surplus has closed and is now out of business - 2020.) I was told about the receiver by a visitor to our museum who had seen it at Twin City the day before. To my surprise, in Reno the following day, the CR-91 was still there. It looked in good shape and was installed in a Scott SLR cabinet (actually a Navy RCH receiver cabinet.) After a little haggling, I purchased the receiver for $125. The CR-91 was setting up on a high shelf that was about six feet off the floor at the rear section of the surplus store. To my surprise, the store employee grabbed a small (but stout) wooden box, placed it on the floor in front of the shelf, stepped up on top of the box and then proceeded to grab the CR-91and pull it off the shelf (that was about shoulder-level when standing on a box.) Keeping his arms extended and holding the CR-91 out at chest-height, he stepped off of the wooden box and, without pausing, carried the CR-91 (still chest-high with arms extended) up to the front counter, 25 yards away. I was impressed, even though the guy did look like he could bench-press 300 pounds pretty easily.

Since the AR-88LF and the CR-91 are designed for a substantial LF antenna of 200 feet or about 500 to 700 pf of capacitive load, performance in that part of the spectrum will suffer with a small antenna. I use my 135' center-fed tuned dipole with the feed line shorted together and fed to the antenna as an unbalanced load. This could be acting as a 43 foot vertical with a large capacity hat, kind of like the old style "T" antenna. Anyway, it seems to work quite well with the CR-91. A tuned loop antenna will work wonders on a superhet receiver providing lower noise reception and directional characteristics. I highly recommend using earphones for NDB reception.

During an evening and a short morning listening sessions this past February (2010) I was able to tune in around 50 or so NDBs with the CR-91. The best DX was YQA 272kc located in Muskoka, ON, Canada, about 2000 miles from Nevada. Best airport beacon DX was SYF 386kc in St. Francis, KS. This was somewhat past the optimum winter conditions of December and January. The advantages of the CR-91 are an accurate tuning dial and plenty of sensitivity. The disadvantage is that the CR-91 is pretty noisy in the LF/MF part of the spectrum. Next season, I'll be trying the CR-91 on the tunable loop antenna.*

Summing up the 2022 CR-91 MW Reception Testing using a Pixel Loop Antenna - The MW Reception Test started on January 21, 2022 and ran until February 3, 2022. The test consisted of six listening sessions with each session running about 30 minutes with the time usually being from 2200hrs to 2230hrs PST. 57 different NDBs were heard during the testing and 117 total (counting stations heard on more than one session) NDB stations were received. Best DX to the East was YKQ 351kc in Waskaganish, Quebec, Canada. Best USA DX East was FIS 332kc in Key West, Florida. Best DX West was LLD 353kc in Lanai City, Hawaii and POA 332kc in Hilo, Hawaii. The TRIMM Hi-Z Phones shown were used for reproducers.

CR-91 during the 2022 MW Reception Testing

Conclusion

Today, the AR-88 series of receivers have world-wide admiration, not only for their WWII historical significance but also for their tremendous performance capabilities and fabulous audio reproduction. AR-88s and their variants can still be found in AM ham stations where they are providing marvelous audio reproduction of quality AM signals transmitted from classic ham AM transmitters and even from the retired AM BC transmitters that several hams operate today. For the dedicated SWLs, the AR-88 receivers still can dig out some of the weakest of SW signals, especially from CW-based utility stations. Of course the audio from quality SW-BC stations can be a listening pleasure. The MW enthusiasts find that the AR-88LF, CR-91 and CR-91A provide excellent reception of Non-Directional Beacons or 630M ham signals. The AR-88's robust construction, which resulted in a receiver that weighed nearly 100 pounds in the cabinet, has somewhat curtailed the easy exchange of surviving examples due to expensive shipping rates. And, even the 75 pound, "out of the cabinet" examples can be a challenge to pack safely. However, the AR-88's superior audio, great sensitivity and fabulous "looks" has resulted in many devoted fans from around the world that are willing to pay for shipping or are willing to travel great distances to pick-up one of these incredible receivers. The AR-88 was a milestone classic of radio design and the surviving examples are still reliably providing great radio signal reception just as they did 75+ years ago.

Hardcopy Material

1. RCA Manuals for NAVY MODEL RDM, AR-88D, CR-91 and CR-88
2. U.S. Army Signal Corps Manual TM 11-899 - R-320/FRC (RCA SC-88)
3. "Diversity Reception" by Murray G. Crosby, March 1933 Radio News - Article on the history of Diversity - Crosby worked for Harold Beverage at RCA
4. "Radio's 100 Men of Science" by O.E. Dunlop - Details on Beverage and Peterson's Diversity work for RCA
5. The Short Wave Magazine, "Getting the Most From Your AR88" by D.M.Gill 4S7MG, Aug 1958 - Servicing, Adjustment and Maintenance
6. The Short Wave Magazine, "Getting the Upmost from the AR88" by W.K.Miller G6QF, Aug 1953 - Calibration, IF and RF Alignment, Checks and General Testing
7. The Short Wave Magazine, "Servicing the AR88" by Harry Leeming G3LLL, Oct & Nov, 1965 - Ideas from Practical Experience with "D" and "LF" Models
8. Electric Radio - "RCA AR-88 - A Classic in Radio Design" by Sam Thompson W6HDU, July 1990 - General Information
9. Radio Bygones - "Rebuilding an AR-88D" by John Wells, Dec 1992 - Mostly information on types of problems found with AR-88s in Great Britain
10. Short Wave Magazine - "Buying and Renovating the AR88" by Harry Leeming G3LLL, August 1993 - General information and some simple modifications
11."A Biographical History of the AR-88, RCA's World Class Communications Receiver" by Bob Haworth W2PUA, OTB Vol.32, May 1991, No.1 - general info, plus info on Lester Fowler
12. RCA "Supplemental Instructions for Aligning AR-88 I.F. Stages in the Field" - Internal RCA Tech Note ca. 1942 - Details on sweep alignment of the AR-88 IF stages

Web Material

1. www.radiomarine.org - Header Photo of Fred Baxter at KPH - Great photos and history of RMCA's KPH
2. www.radiojamming.info  - DR-89 photo, Vilnius, Lithuania - Interesting website on history of radio jamming in Eastern Europe during the Cold War
3. www.portsdown-tunnels.org.uk  - WREN photo and history of the Portsdown Tunnels - Comprehensive history of Portsdown Hill in Great Britain
4. www.jproc.ca/rrp/stadacona_ve1ho  -  photo of  VE1HO, Stadacona, NS, Canada - Short history of VE1HO
5. www.radiovaticana.org  - photo of their CR-88B - lots of photos relating to the Vatican shortwave radio station
6. www.jproc.ca/rrp/whitehorse_radops.html  - photo of CR-88A and SP-600JX - lots of photos and information on the RCAF Whitehorse Listening Station. Jerry Proc's website is comprehensive on the communications radio history of Canada. An excellent source of information with great original B&W photos.
7. Wikipedia - Lend-Lease Act of 1941 - Details on Lend-Lease Act
8. VMARS - UK Manual Source - reference #1217 to #1221 for E773 - British Manual available as PDF - details on AR-88 series circuit with voltage charts

Hearsay

1. Thanks to Alan Ford, VK2DRR for providing his AR-88D, F and LF serial number logs and his thoughts on the RCA serial number methodology 
2. Thanks to the many AR-88 enthusiasts who, over the years, have related their stories and other information either by telephone, over the airwaves, via the web or in person
3. Thanks to UA1OSM - Serge provided photos of UA-UK hams with AR-88 receivers and the history of AR-88 in Russia and information on Russian military receivers
4. Thanks to Mike Student W7MS for the Remote Muting Mod info

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