[Milsurplus] Collins 75A-4 Receiver Coverage

[Mike Morrow]

Al wrote:

>I think the answer is that the 75A was introduced in 1946.  (per Moore, 
>3ed Edition)  This was the first commercial double-conversion superhet 
>with a crystal controlled first oscillator.  This gave it unprecedented 
>frequency accuracy.  The 51J was developed from the 75A and wasn't ready 
>until 1949.

That is going back a little too far.  That was in the ALL AM/CW/RATT era.
I don't think there was much military usage of ham gear for those circuits.

The motivation for USAF and USN use of the specific 75A-4 model receiver
arose in the mid-1950s and hinges on it being *designed* for the SSB mode
of operation.  In that respect, it was *unique* in the Collins catalog of
ham, commercial, or military receivers in 1955.  The other 75A and all
51J (even 51J-4) models were not designed for SSB operation.

In 1957, Lt. Gen. LeMay mandated the conversion of USAF long-range
communications to SSB.  Special 75A-4 receivers that covered some non-ham
bands (described in recent postings) were part of that process.

The USAF and USN purchase of custom versions of the 75A-4 leads one to assume 
that the KWS-1 transmitters that were also purchased were likewise customized
in frequency coverage as well.  Perhaps some list members know and will confirm.

Another question arises about the 1957 conversion of USAF communications to SSB.
What sets were installed in the aircraft?  Obviously, ground gear like the 75A-4
and KWS-1 could not serve in any regular airborne configuration.  The first
widely installed USAF aircraft SSB sets were the RCA AN/ARC-65 and the Collins
AN/ARC-58, but I don't believe these appeared until the very late 1950s.  I am
not aware of any earlier airborne SSB units.  Even the USN's first widely used
SSB set, the Collins/RCA AN/ARC-38A, did not appear until the late 1950s or
early 1960s, not long before the excellent Collins 618T (IMO, the most important
airborne HF set of all time) saw first light of day.

There is documentation of KWM-1 installation in some special aircraft like the
CIA U-2, but a KWM-1 would not satisfy regular military communications needs.

So, what gear was on the flying end of those USAF comm circuits using those
ground-based custom 75A-4 and KWS-1 sets?

Mike / KK5F