[ARC5] HF SigInt, airborne platform

[Mike Morrow]

Mike Hanz wrote:

>We also need to be a little more focused on time lines when we are 
>talking about intent, IMO.  The GO-5 and GO-6 acquisitions were 
>superseded by the GO-7, -8, and -9 by the time this little requirements 
>group met in the Autumn of 1939, if I read the tea leaves on that series 
>correctly, so the need for RAX Unit No. 3 as strictly a liaison receiver 
>requirement *for the last half of 1940* would seem a little puzzling.

Mike,

Here's my take on the equipment time-line issue:

USN Liaison Transmitter History
(1)  GO-3 was made by Westinghouse.  Its max frequency was 13575 kHz.
     The contract date was 1937.
(2)  GO-4, GO-5, and GO-6 were made by General Electric. Their max frequency
     was 26500 kHz.  The contract date for GO-4 was 1938, and for GO-5 and
     GO-6 was 1939.
(3)  GO-7, GO-8, and GO-9 were made by Westinghouse.  Their max frequency
     was 18100 kHz.  The contract date for all three was 1940.

USN Liaison Receiver History
(1)  The RU-6 was the standard and most recent liaison receiver that was
     contemporary with the GO-3 in 1937.  It was made by A.R.C., and its
     max frequency was 13575 kHz.  There was full liaison transmitter
     frequency coverage by the A.R.C. RU-6 and earlier versions.
(2)  No USN receiver existed in 1938 to match the coverage of the GO-4
     above 13575 kHz. The same applies to the GO-5 and GO-6 in 1939.
     Then, the RAT or RAT-1, contract date 1939, became (potentially)
     available from A.R.C. to cover the full range of these new liaison
     transmitters using A.R.C.'s RU-10 (1938), RU-11 (12v, 1939), or
     RU-12 (24v, 1939) PLUS A.R.C.'s new RAT (12v) or RAT-1 (24v).
     The RAT/RAT-1 almost **exactly** covers the missing liaison receiver
     spectrum when used with the GO-4, GO-5, and GO-6, beginning at
     13500 kHz (just below the RU's max frequency) and ending at
     27000 kHz (just above the GO-4, -5, or -6 max frequency).
(3)  It would be likely that A.R.C. would propose a complete set of liaison
     receivers covering the full frequency range of *any* recently introduced
     version of the GO.  This design would be based on the RAT-1 design and
     replace the RU-12 plus RAT-1 for 24v liaison service.  The resulting
     set was the RAV, contract date 1940.  
(3)  It would be likely that General Electric, also seeing a need to provide
     a liaison receiver for *their* version of the GO transmitters, would
     design a set with full coverage from 200 to 27000 kHz. The resulting
     set was the RAX and RAX-1, contract date 1940.

The three-receiver RAX/RAX-1 would have had a great many advantages in liaison
service over the A.R.C.'s RU plus RAT or RAV competition.  It is not surprising
that only about 50 each of the RAT and RAV sets were acquired by the USN before
they were abandoned.

The lowering to 18100 kHz for the max frequency coverage of the 1940 Westinghouse
GO-7, -8, and -9 should NOT have spurred any change in the design specifications
of A.R.C. or GE for liaison receivers produced in 1940 or later.

It seems highly unlikely that someone at A.R.C. in 1938/1939, seeing a need to
provide a hypothetical ELINT-service receiver set, selected frequency coverage
that began at an odd 13.5 MHz and ended at an equally puzzling 27.0 MHz.  But that
same coverage, serving a liaison-service need, fits the required spectrum missing
above the RU-12 like a glove.

It's very difficult for me to conclude anything other than A.R.C.'s RAT/RAT-1
frequency coverage was determined in the design phase by a need for A.R.C. to
provide this capability along side the RUs that they supplied for naval aircraft
liaison service.  I believe that if one were fortunate to have a RAT or RAT-1
set, it should be accompanied by a RU-11 or RU-12 to properly complete the most
likely *intended* configuration for the liaison receiver serving with a GO-4, -5,
or -6 liaison transmitter...or for that matter, serving with any liaison transmitter
(GO-7, -8, -9, ATC/ATC-1) covering above the RU's top limit of 13575 kHz.

Likewise, it's very difficult for me to conclude anything other than GE's
RAX/RAX-1 frequency coverage was determined in the design phase by a need for
GE to provide this capability in a liaison receiver installation to serve with
their GO-4, -5, or -6 liaison transmitter installation.  For later transmitters,
the value of the third RAX-1 receiver, the CG-46117, is that it was the USN's
only liaison receiver capable of matching the frequency coverage of the GO-7,
-8, -9 and the ATC liaison transmitters to 18100 kHz.  Without it, more than
half the spectrum of these transmitters would be without any possible use. 
 
Once again, I make no speculation on how the frequency coverage of any of these
sets was ultimately utilized.  My interest is in the reason behind the *design*
of receivers with this coverage.  Frankly, I've seen absolutely NO convincing
argument that ELINT was even the smallest motivation for the design of these
receivers covering up to 27 MHz.

Mike / KK5F