[ARC5] MF/HF "Command" Set Receiver History vs. Hacks By The Military

[Mike Morrow]

Wayne wrote:

> Y'all please note that in WWII they "hacked" the equipment too. As the 
> esteemed Mr. White described in his legendary articles, USAAF techs 
> produced 9-13, 20-27 MHZ and 30-40 MHZ versions of BC-455's.

Wayne, there's a little being left out of this story, and there's a
problem with the sequence of events.  Let me outline a limited history
of the receivers from these sets, as I understand it.
  
Knowledgeable authors have shown that development under US Navy contract
of the ancestor to receivers now known as "command sets" began as early as
1936 by A.R.C. as the Type K command set.  This was not a production set,
and apparently the design, as far as it went, was concluded by 1938.  See
Mike Hanz's fascinating page http://aafradio.org/NASM/Hmmmm.html for a look
at the four Type K receivers, covering:
Type K Model 2 ( 200 to  575 kHz)
Type K Model 2 ( 520 to 1500 kHz)
Type K Model 2 ( 3.0 to  6.0 MHz)
Type K Model 2 ( 6.0 to  9.0 MHz)

A production two-receiver system was made by A.R.C. in 1939 under USN
nomenclature as RAT (12-vdc) and RAT-1 (24-vdc).  One receiver (RAT/CBY-46083
or RAT-1/CBY-46108) covered 13.5 to 20.0 MHz and the other (RAT/CBY-46084
or RAT-1/CBY-46109) covered 20.0 to 27.0 MHz.  These are the FIRST 
non-development versions of Type K designs that ultimately became THE 
"command sets", made in the millions by 1945.  Conclusions may differ,
but I believe available hard evidence suggests that the RAT/RAT-1 was designed
to supplement the receiving range of the RU-11/12 liaison receivers (made
also by A.R.C. in 1939).  A.R.C.'s RU-4/5/6/10/11/12 liaison receiver
coverage ends at 13.575 MHz, which is also where frequency coverage of the
Westinghouse 1937 GO-3 and earlier GO liaison transmitters ends.  But the
upper frequency range of General Electric's 1938 and 1939 GO-4/5/6 liaison
transmitters extends to 26.5 MHz.  A receiver system was needed to cover
that gap.  A.R.C. built the new Type K based 13.5 to 27.0 RAT/RAT-1
to precisely match (when used with the RU-11/12) the coverage of the
latest associated liaison transmitters.  A.R.C. didn't build many.
Just 50 each of RAT and RAT-1.  But, it's doubtful that many GO-4/5/6
transmitters were built either.  The GO was appropriate only for large
patrol aircraft in the late 1930s.

The ONLY receiver covering 9.0 to 13.5 MHz is the CBY-46107.  It one of eight
receivers in the 1940 24-vdc RAV system.  I believe that the RAV was designed as
A.R.C.'s late-1930s liaison receiver system to totally abandone the 1930-era
RU system.  It was not provided with components for remote control,  The RAV
covers the whole range of the contemporary GO-4/5/6 liaison transmitters by
using the latest Type K based receivers.  It thus would replace the RU-12 and
RAT-1 receiver system.  The RAV receivers are: 
CBY-46102 ( 190 to  550 kHz)
CBY-46103 ( 520 to 1500 kHz)
CBY-46104 ( 1.5 to  3.0 MHz)
CBY-46105 ( 3.0 to  6.0 MHz)
CBY-46106 ( 6.0 to  9.1 MHz)
CBY-46107 ( 9.0 to 13.5 MHz)
CBY-46108 (13.5 to 20.0 MHz)
CBY-46109 (20.0 to 27.0 MHz)
Notice that the CBY-46108 and -46109 were also part of the RAT-1.  There
was no 12-vdc version of the RAV.

Only 46 RAV sets were made.  The CBY-46107 is one of the great rarities
of the "command sets", even though it wasn't a command set.  It, with
the CBY-46102 and -46103 (which should be equally rare) were used ONLY
in the RAV system.

In 1940, A.R.C. developed the first "command set" version of the Type K
based designs.  That, of course, is the ARA, consisting of five receivers:
CBY-46129 ( 190 to  550 kHz)
CBY-46145 ( .52 to  1.5 MHz)
CBY-46104 ( 1.5 to  3.0 MHz)
CBY-46105 ( 3.0 to  6.0 MHz)
CBY-46106 ( 6.0 to  9.1 MHz)
Notice that the last three receivers were also part of the RAV system.  The
first two ARA receivers (CBY-46129 and -46145) are identical to the first two
RAV receivers (CBY-46102 and -46103) except that the loop connection posts
and switch have been removed on the ARA version.  The ARA command receiver
system, unlike the RAV liaison receiver system, was provided with components
required for remote control, and apparently NO local control adapters.

In 1941, A.R.C. developed the USAAF version of the USN's ARA/ATA command set.
That, of course, is the SCR-274-N, consisting (ultimately) of four receivers:
BC-453-A/B ( 190 to  550 kHz)
BC-946-B   ( .52 to  1.5 MHz)
BC-454-A/B ( 3.0 to  6.0 MHz)
BC-455-A/B ( 6.0 to  9.1 MHz)
Electrically, SCR-274-N components are identical to the ARA/ATA equivalents
except that the ARA/ATA utilized low impedance AF (600 ohm) while SCR-274-N
-A model components utilized high impedance AF (8000 ohm).  Later -B model
components could be wired for either high or low impedance AF.  Paint finish
and minor mechanical details, plus the remote switch on the antenna relay,
offer other minor differences between ARA and various versions of the SCR-274-N.

In late 1943 the US Navy received the first units of the "improved" ARA, the
final MF/HF command set system used by the USN.  This is the AN/ARC-5.
Ignoring VHF components, these are:
R-23/ARC-5 ( .19 to  .55 MHz) [or improved R-23A/ARC-5]
R-24/ARC-5 ( .52 to  1.5 MHz)
R-25/ARC-5 ( 1.5 to  3.0 MHz)
R-26/ARC-5 ( 3.0 to  6.0 MHz)
R-27/ARC-5 ( 6.0 to  9.1 MHz)
R-148/ARC-5X ( 190 to  550 kHz) [12 vdc version of R-23A/ARC-5]
The loop posts/switch of the RAV re-appeared on the R-23 and R-24.  The R-23
and R-24 were also wired to support, using audio adapter panel MX-19, the
short-lived Air-Track ILS (AN/ARN-9) as a localizer receiver.  All receivers
had real AVC, which required a minor change in tube line-up.  Most R-25 to
R-27 receivers were "stabilized" to allow locked preset fix-tuned operation.

The ony post-war legacy of the MF/HF Type K design is the commercial and military
A.R.C. Type 12 LF/MF navigation receivers:
R-11A ( .19 to  .55 MHz)
R-10A ( .52 to  1.5 MHz)
R-22  ( .52 to  1.5 MHz)

Reference is made to BC-455-B receivers modified for VHF.  A few were modified
to cover 28 to 41 MHz for the potential of using the German "Sonne" radio beacon
system.  This was based on the pre-WWII German commercial "Lorenz" beacon system.
There doesn't seem to be much indication that this effort was more than
exploratory.  (It wouldn't seem prudent to depend on a system operated by one's
opponent!)  I doubt that the modifications made to the BC-455-B were made by
a bunch of USAAF radio techs just "messing around" like hams.  It would
be interesting to know what organization made how many of these conversions,
but the frequency dials were reported as re-calibrated for 28 to 41 MC,
something not likely to have been carried out by any outfit performing a "hack".
Gordon White addressed a number of such details in "CQ", June 1968.

So...none of the frequency ranges that were mentioned are the result of "hacks"
by anyone.  Except for the "Sonne" modifications of the BC-455-B, the cited
frequency ranges represent those for which the receiver was specifically
designed and manufactured.

>Would hacking a unmodded set to produce one of these rare versions not be a 
>worthy endeavor?

Obviously not.  It wouldn't be possible, even if one wanted to.

Mike / KK5F

I would be gratified for the opportunity to correct any of the narrative that
I have provided upon demonstration that other rationale existed in the **design
and production** phase of the systems discussed.  Please!