[Milsurplus] [MMRCG] Speculations on ground radios of the fifties
John Vendely
jvendely at cfl.rr.com
Thu Apr 30 09:20:29 EDT 2026
Howdy,
If I recall correctly, the ARC-21/ARC-65 conversion article was in the
Dec. 1956 IRE Journal, which was a special single sideband issue. I
have it around here somewhere and will try to dig it up. It also
contained a detailed article about the ARC-58.
Regarding the ARC-38A, I overhauled three of them back in the mid 1980s
for use in a Lockheed P2V-7 owned by the Indiana Museum of Military
History which we flew on the airshow circuit. I made many contacts and
some phone patches back to the Museum on long flights, and we had a
lotta fun with it. RCA did an excellent job on the SSB conversion, and
I found the ARC-38A to be an excellent performer, though the SMO system
did require the periodic TLC typically required of all synthesized sets
of the time. An unsung feature of the ARC-38A was its very effective RF
clipping speech processor, one of the earliest such processors I'm aware
of.
There was an excellent article on our restoration and operation of this
aircraft in the April 1987 issue of Sport Aviation...
73, John K9WT
On 4/30/2026 3:23 AM, Jim Whartenby via Milsurplus wrote:
> Mark
> I know of an article about the conversion of the ARC-21 to SSB that
> was in the "RCA Engineer", April 1963. Do you know the year and date
> of the IRE article?
> Jim
>
> Logic: Method used to arrive at the wrong conclusion, with confidence.
> Murphy
>
>
> On Wednesday, April 29, 2026 at 07:19:59 PM CDT, boeing377 at gmail.com
> <boeing377 at gmail.com> wrote:
>
>
> The ARC 21 to ARC 65 conversion is the subject of a very interesting
> article in the journal of the IRE, Institute of Radio Engineers.
>
> When I was much younger, I tried getting an ARC 65 on the air. I was
> able to get the receiver working and it was a VERY good HF receiver,
> but I never was able to get it to transmit.
>
> Mark
> AF6IM
>
>
> On Wed, Apr 29, 2026 at 1:32 PM Jim Whartenby via Milsurplus
> <milsurplus at mailman.qth.net> wrote:
>
> Ray
> The first airborne synthesized, fully automatically tuned, HF
> transceiver would be the ARC-21, made by RCA. It is an AM
> transceiver or "double sideband" as RCA would describe it which
> was also capable of CW operation. It also used RCA designed
> mechanical filters, two as IF filters and one as the BFO
> oscillator for CW operation. Perhaps this is the first use of
> mechanical filters in a military radio? It does not use 400 cycle
> power as all of the servo tuning systems are DC powered. It is
> capable of 100 watts RF output over the frequency range of 2 to 24
> mc with 500 cycle increments over all frequencies. It was
> designed for the first jet bomber, the B-47 and it's support aircraft.
>
> Some five years or so later, SSB became the main mode for
> communications so in order to recoup the investment in equipment
> already on hand, the ARC-65 was developed. This modification was
> done by replacing the modulator, power amplifier and reference
> oscillator with most of the other modules of the ARC-21 remaining
> with appropriate modifications. With this successful experience,
> RCA was tasked with doing the same for the ARC-38.
>
> The ARC-21 is listed in JANAP-161 as is the 618S-1 but not the
> ARC-38. I'm not sure why this is so as it is my understanding
> that the ARC-38 was in development before the release of the
> 618S-1. Perhaps the ARC-38 was only used by the Navy so it was
> not listed in JANAP 161? Both are wired to accept the SMO, servo
> amplifier and 500ks oscillator, IIRC, so I suspect that both were
> in development concurrently by Collins.
>
> As for the Army not converting to SSB, weren't they more impressed
> with VHF FM?
> Regards,
> Jim
>
> Logic: Method used to arrive at the wrong conclusion, with
> confidence. Murphy
>
>
> On Wednesday, April 29, 2026 at 10:05:12 AM CDT, Ray Fantini via
> groups.io <http://groups.io> <rafantini=salisbury.edu at groups.io>
> wrote:
>
>
> Want to Thank Nick for posting the info on the R-808 and GRC-14,
> over the years have owned a couple of radios but never any of the
> GRC-14 family of components. Would assume that it's somehow a
> competitor of the GRC-19, R-392/T-195 but never as successful. The
> ARC-38, 618, T-195 and T-631 are all using the dual winding servo
> tuning systems along with 400 cycle Chopper / Discriminator
> systems for PA and Antenna tuning, maybe the first true Autotune
> system developed. Remember that allegedly autotune radios like the
> ART-13 and the like are only radios with mechanical presets where
> the servo radios like the ARC-38 have a true automatic tuning
> system that thru the use of discriminators can arrive at a
> solution for PA and antenna resonance.
> Spent many hours learning the ways of the ARC-38 and 180 L tuners,
> dealing with phase relationships and mechanical conversions of
> small DC voltages to high AC voltage to drive system. Similar
> system on the T-195 and the 618 family of SSB transceivers. The
> GRC-106 amplifier employes the same idea of discriminators and
> resonance balance but relies on the operator to be the motor.
> A weird quirk of the T-195 was that they pushed the capability of
> the autotune a little too far maybe and occasionally the radio
> would not achieve a tuning solution, I always suspected that this
> was a result of attempting to do both PA and Antenna match in one
> stage. Don't know if that's the case or not. But looking at the
> design of the GRC-14, they may have resolved that issue. It's
> going to annoy and aggravate a bunch of people out there but just
> looking at the manual have to say that although I never worked on
> or used the GRC-14 it may be a superior set to the Collins GRC-19,
> but at least the GRC-19 is lighter than a GRC-14 and smaller too.
> GRC-19 sets were everywhere, least until the death of AM and still
> held out in RTTY ops until the GRC-106 came along but the GRC-14
> appear to only have limited use and were quickly phased out as
> soon as SSB was adapted as a standard. Too bad no one ever reverse
> engineered the GRC-14 sets for SSB like the ARC-38A
> Another question would be why the ARC-38A happened ? The basic
> ARC-38 was a groundbreaking autotune transceiver with its
> self-tuning , variable IF and mechanical filters. It was years
> ahead of anything else out at the time. But by the sixties
> everyone knew SSB was the way HF communications were going, and
> the 618T was still in development, so how did it happen that
> someone decided to do the huge conversion from AM to SSB? And why
> when it was a Collins design, did RCA get the job? I like how RCA
> would also paint over the front cover, so you would no longer see
> the big Collins logo or name.
> Also have to wonder why there was no attempt to re fit the
> R-392/T-195 (GRC-19) for SSB? Once again just looking at the book
> think it would have been easy to re-work the GRC-14 stuff then
> deal with how densely things were stuffed into the GRC-19
>
>
> Ray F/KA3EKH
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