[ARC5] [Milsurplus] RAX-1 Contract Information

[Mike Morrow]

> "On contracts NOs-74810, NXs-15298, and NXsa-36561, all three Radio
> Receiver Units (Navy Types CG-46115, CG-46116, and CG-46117) are
> supplied and dynamotor units are included. On contract NXsa-77864 and
> N5sr-11815, only Radio Receiver Unit 2 (Navy Type CG-46116) is
> supplied and the dynamotor is included only with a portion of these
> contract lots."
>
> Makes you wonder how they powered these single receivers if they
> didn't already have a dynamotor on hand. Special outboard supply? Why
> only one receiver? Specific use or spare/backup receiver?

I would suggest that contracts NOs-74810, NXs-15298, and NXsa-36561 procured
the complete set for initial installation in new aircraft or older aircraft
that were getting the RAX-1 for the first time.

It is likely that the partial equipments supplied on NXsa-77864 and N5sr-11815
were simply for replacement purposes only, with the type and number of
components procured based on actual service history of the need for such
replacements.

The CG-46116 (1.5 t 9.0 MHz) would have normally been the receiver that got
the most use (by far) in liaison service.  The CG-46115 (0.2 to 1.5 MHz)
would likely have been almost never needed in the Pacific.  There
doesn't appear to have been much in the way of beacon or broadcast band
transmitters in the Pacific.  And, had there been, the lack of pilot
control of a RAX-1 would make its use awkward.  The pilot-controlled
ZB-* or AN/ARR-2 would have provided homing capability to YE/YG beacons.
The CG-46117 (7.0 to 27.0 MHz) may hake seen some use for liaison service
if the upper frequency ranges of a GO-* or ATC were utilized, but not so
often as the CG-46116.  I suspect that often, the CG-46116 was the only
one of the three receivers that was even turned on in flight. It makes
sense to me that the CG-46116 would more often require replacement in the
three-receiver system.  I wouldn't interpret these single-receiver contract as indication that there were a lot of single-receiver aircraft installations.

> You guys know FAR more about this stuff than I do, but just looking at
> the basic design of a RAX-1 receiver, it's not difficult once the
> basic unit is made to tailor it for full HF coverage from beacon band
> to frequencies approaching low band VHF, and in only 3 receivers with
> greater coverage than the ARC-5 group as Mr Morrow points out.

I ("Mr." not needed :-) ) made no comparison between the liaison service RAX-1
versus the command service AN/ARC-5.  The interchange of one for the other would
not be optimal in any associated system.

What I  attempted to suggest is that our beloved "command set" evolution,
including the choice of frequency coverage, likely proceeded as follows:

(0)  A.R.C. develops the Model K antecedent in the mid-1930s.

(1)  Westinghouse produces in the late 1930s the GO-4 to GO-6
     liaison tranmitters with coverage to 26.5 MHz.  A.R.C.'s RU-*
     receiver coverage ends at 13.575 MHz, so A.R.C. proposes the
     RAT and RAT-1 (13.5 to 27.0 MHz) to provide the additional
     liason receiver coverage.  This is the first military
     generation of Model K receivers.

(2)  A.R.C. then proposes a liaison receiver system based on the
     two-receiver RAT-1 system that provides all the coverage of
     the RU-* with RAT.  The result is the eight-receiver RAV
     providing liaison receiver coverage from 0.19 to 27.0 MHz.
     This is the second military generation of Model K receivers.

(3)  G.E. produces an competing design as the three-receiver RAX
     design that covers essentially the same range as the RAV and
     is smaller, lighter, simpler, and higher-performance.

(4)  The RAT-* and RAV fail to be procured for liaison service due
     to the many advantages of the RAX design.  However, the first
     two receivers of the RAV become part of the ARA after design
     modification to eliminate the loop connections.  The third to
     fifth RAV receivers become part of the ARA without ANY changes.
     These five receivers are now for "command set" service.
     This is the third military generation of Model K receivers.

(5)  A design improvement of the ARA is incorporated as these five
     modified receivers become part of the AN/ARC-5.  This is the
     fourth military generation of Model K receivers.  It is also
     the final generation, discounting post-war VHF sets.

This suggests that usage for liaison service, morphing into usage for
command service, is the ONLY explaination needed for why these receivers
(including the RAX) exist in the ranges for they were provided.  If later
liaison transmitting equipment did not make use of coverage to 27.0 MHz,
that does not form a basis for suggesting that such coverage was designed
into the set explicitly for ELINT service.

My interest is with what motivated the design specifications for these
receiver systems.  I don't believe that ELINT service was any part of that
design motivation.

But...that doesn't mean that advantage was NOT taken of the coverage for
ELINT.  I am making NO claims contrary to the research of others that
indicates these sets found usage in ELINT service.  My point can be summed
up as:  "They don't appear to have been *designed* for ELINT service."

> Overly simplified, and in no way would it address any ELINT roles, but
> one has to wonder - why bother with the CG-46117 receiver otherwise?

I'd suggest:

(1)  Allows use of the RAX-1 up to the full 18.1 MHz of the GO-7 to -9,
     or the ATC.  Using only a CG-46116 would limit liaison system usage
     to below 9 MHz.

(2)  The 27 MHz upper end was a legacy from an earlier design specification
     that was established as outlined above when liaison receiver coverage
     was needed for transmitters operating up to 26.5 MHz. 

I've gained a lot of respect for the RAX-1, especially compared to other
US Navy aircraft receivers like the ARB.  But for a locally-controlled
liaison receiver, it's hard to understand why the US Navy didn't just
adopt the best aircraft receiver design of the era...the BC-348, especially
after it was decided to limit liaison transmitter coverage to 18.1 MHz.
Perhaps it was thought that without coverage of 540 to 850 kHz for potential
use with a ZB-* homing adapter, it wasn't suitable.

Mike / KK5F