[ARC5] Jeeps with Radio Equipment

Sat Jul 31 17:24:07 EDT 2021

The 1939 A.R.C. RAT and RAT-1 covered 13.5 to 27 MHz.  They were liaison receivers that extended coverage of the 1939 A.R.C. RU-11 (12v) and RU-12 (24v) liaison receivers, which ended at 13.575 MHz.  There existence was prompted by the frequency coverage of their associated liaison transmitters GO-4, -5, -6.

The extended frequency coverage was required because the contemporary GE-made (1938, 1939) liaison transmitters GO-4, -5, and -6 had coverage to 26.5 MHz.  RAT and RAT-1 provided just enough coverage to overlap the RU-11/12 end at 13.575 MHz and extend just beyond the GO-4, -5, -6 end at 26.5 MHz.  That rather odd 13.5 MHz to 27.0 MHz coverage of RAT and RAT-1 had a very definite well-defined basis for its selection.

The 1940 A.R.C. RAV liaison receiver set replaced ALL of the RU set coverage with six receivers similar to RAT-1 that covered 0.19 to 13.5 MHz, plus the two original RAT-1 receivers now designated RAV.  RAV was 24 vdc only.  The RAV was A.R.C.'s dying gasp attempt to produce a satisfactory liaison receiver with coverage to 27 MHz.

In 1940 the first two RAV receivers were modified to remove the loop antenna posts and switch, becoming ARA command set receivers.  The third, fourth, and fifth RAV receivers were adopted with NO change except nomenclature as ARA receivers.

Thus, ALL of the receivers which became "command sets" were first produced as part of an A.R.C. liaison receiver system.

The RAV was decidedly defeated by GE's RAX-1 liaison receiver set, which covered the same range with three receivers of better design (the receiver that covered the upper ranges had one more RF amp and one more IF amp, compared to RAV), much better bandspread, three instead of eight dynamotors, almost half the vacuum tubes, in a smaller volumn and weight and lower power consumption.  That is why RAV components are great rarities, especially the 9 to 13.5 MHz CBY-46107...none of the 50 appear to have survived intact.

The ARA receivers except the one for 1.5 to 3.0 MHz were adopted (eventually) as SCR-274-N receivers, identical except for AF impedance and wiring of the front panel connector.

The AN/ARC-5 MF/HF receivers were improved versions of the ARA equivalents, including more wiring changes at the front panel connector and the return of the RAV's loop antenna posts and switch on the first two receivers.

There is indeed a 12v receiver in the AN/ARC-5 system...the R-148/ARC-5X.  That is the 12v equivalent of the R-23A/ARC-5.

Mike / KK5F

-----Original Message-----
From: J Mcvey <ac2eu at yahoo.com>
Sent: Jul 31, 2021 2:12 PM
To: Captain D. <mkdorney at aol.com>, Tim <timsamm at gmail.com>
Cc: ARC-5 List <arc5 at mailman.qth.net>
Subject: Re: [ARC5] Jeeps with Radio Equipment

The ARC-5 series were ALL 28V aircraft radios.
However there was a "RAT" series of receivers which covered 20 meters and up to 27 Mhz.
They were 12v receivers that looked like ARC-5 , but had no matching transmitters.
The ARC-5 series stopped at 40 meters in the HF band.

The dual 12v batteries and maybe a APU to charge them must have been how they did it.
I doubt they modified the radios for 12V . 

Besides, those radios would have drained the jeep battery pretty fast.

On Saturday, July 31, 2021, 2:25:14 PM EDT, Tim <timsamm at gmail.com> wrote:

If you look at the Iran photo VERY carefully you can see the jumper cables running from the C-87 Put Put APU over to the jeep battery bank...

(Sorry, couldn't help myself!)

Tim
N6CC

On Sat, Jul 31, 2021 at 11:18 AM Captain D. via ARC5 <arc5 at mailman.qth.net> wrote:
Radio modification of the transmitters for the ARC-5/ SCR-274 is extremely difficult, but not impossible.  So modification would really depend on the motivation of the tech doing the mod, and his ability to find the parts needed.  If the regular USAAF/USN  radios were not available, then use of an SCR-274/ARC-5 is brought into play.  The photos of the modified vehicles do not positively show a power source, and a 24 volt kit to convert the vehicle electrical system was not available for the MB/GPW ( or the WC-series 3/4 ton vehicles, for that matter) until well after WW2 ended, and there were no 24 volt electrical system 1/4 or 3/4 ton wheeled vehicles factory produced for field use until the 1950s..  I agree that in such a situation, converting the radios to 12 volt is not likely, since parts to do so would not be readily at hand.  So we're left with getting a scrounged generator/APU to supply the 24 volts needed to power the radio/ recharge a bank of batteries to provide the necessary 24 volt power to the radio in the picture.  There is no APU/generator anywhere in the pictures that have been posted to far. The only assumption that can come from that is the equipment used to power the radios/recharge the battery bank was supplied by something not in the pictures.  A trailer mounted generator/APU makes sense, especially and APU.  The APU was already in USAAF inventory, and was commonly used for bomber aircraft.  The APU could be connected to the radios using a theatre made cable with plugs and sockets gotten through regular supply channels, or scrounged from damaged/not airworthy aircraft. 

Mark D.
WW2RDO 

"Courage is not having the strength to go on.  Courage is going on when you don't have the strength."   -  Theodore Roosevelt

Sent from my AOL Desktop

.

In a message dated 7/31/2021 12:59:22 PM Eastern Standard Time, kgordon2006 at frontier.com writes: 
On 31 Jul 2021 at 16:43, Mike Morrow wrote:

> The radios may not be ARC-5, SRC-274 or ARA radios. They may be an
> earlier> look-a-like that ran on 12 volts.Rule that out positively.
> There were no such radios anywhere anytime in military service...ever
> (except the R-148/ARC-5X and its rack... a 14 vdc version of
> R-23A/ARC-5).  When use of an aircraft MF/HF command set was required in
> a 12 vdc environment, the USAAF used the SCR-A*-183 and the USN used the
> appropriate RU/GF system.> Either that, or parts were scrounged and
> radios were heavily modified.This suggestion lacks credibility.The full
> SCR-274-N installation shown in Bill's photo looks like one pulled
> "lock, stock, and barrel" from a USAAF aircraft with no attempt to
> tailor it to just whatever HF capability that jeep may have required.
> (Certainly it did not need a beacon band receiver.)  Just how great
> would be the motivation to locate ten rather uniquely configured 12 vdc
> relays of six different types, install them in five different
> components, rewire filaments in six different components, and rewire
> carbon mic excitation just to be able to install a stock-looking
> complete SCR-274-N in a 12 vdc jeep?  Occam's Razor indicates that the
> ONLY reasonable and logical conclusion is:  That SCR-274-N is being
> supplied 24 vdc.Mike's photo of a custom single receiver single
> transmitter installation provokes these comments:1.  The transmitter
> control box appears to have a built-in key on its top.  Only the ATA
> CBY-/CCT-23243 and SCR-274-N BC-451-A control boxes have a key...the
> very rare C-29/ARC-5 does not.  That indicates the equipment is ARA/ATA
> or SCR-274-N.2.  ALL components have black paint.  That indicates the
> equipment is ARA/ATA or EARLY SCR-274-N.It is equally unlikely that this
> equipment has been reworked for 12 vdc for the same reasons I cited
> above except that only six 12 vdc relays of six different kinds would be
> required.  Anyone performing such a quixotic feat should also have
> realized that a single-transmitter system using only VOICE emission
> requires NO transmitter control box.  Some post-WWII USN training
> aircraft used only the T-19, R-23A, and R-26/ARC-5.  There were C-125
> controls present for the R-23A and R-26, but the ONLY transmitter
> control was the instructor's PTT switch.My conclusion:  The sets in each
> of these photos without any doubt are being supplied 24 vdc.

I absolutely agree with this statement!!!

>  I will not
> speculate from where the 24 vdc comes.Mike / KK5F

Ha ha! **I** will! :-)

Ken W7EKB
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