[ARC5] AN/ARC-3 ?

[Jim Haynes]

Some old war stories...

In addition to the ARC-36 (16 channels) and ARC-49 (48 channels) the
C.A.A. had a version with 24 channels.  All this was done by crystal
switching, so I guess the multiple channels had to be close in frequency
so that one tuning setting would do for all the channels in one crystal
position.

I believe the original aircraft VHF set was the English equivalent of
the SCR-522.  And then the SCR-522 was a U.S. redesign but plug compatible
with the English sets.  Four channels, as also the ARC-4 had, and
early civilian VHF sets.  And the VHF sets in the ARC-5 family.
Four channels gave you one for emergency 121.5, one for control towers,
one for flight service stations, and one left over for some other purpose.
Evidently there was seen to be a need for more frequencies, but not many
more, by the time the ARC-3 was developed.

Then the military was allocated the 225-400 MHz band, and were expected
to clear out of the 108-136 MHz civilian aviation band.  The military
had to furnish GRC-27 UHF equipment to the CAA/FAA so that the air
traffic control system could communicate with military aircraft.  And
the military was forbidden for a time from acquiring any new VHF 
equipment.

I was at Edwards AFB 1960-1963, during that period.  I believe at that
base at least we had got rid of the BC-640 transmitter and BC-639
receiver that were the mainstay of WW-II ground stations.  We had a
bunch of ARC-3 sets with third-pary AC power supplies to meet the
ongoing need for VHF communication.  Part of the need was that we had
a lot of contractor aircraft flying in and out, and they were civilian
and thus carred only VHF equipment.  Another need was for emergencies -
sometimes airliners make emergency landings at Edwards to take advantage
of the long runway extension provided by the dry lake bed.  So we
had quite a number of these 15 year old ARC-3 sets in daily use as
ground stations.

There was also some mission that required flying around Europe from time
to time.  By then the standard civilian VHF equipment was frequency-
synthesized and could operate on hundreds of frequencies at the turn
of a dial.  And ground stations had set up on frequencies all over the
civilian band - every tower having a different frequency, every other
kind of communication facility using lots of frequencies (as they do
today).  Since the only VHF equipment we were allowed to put in the 
airplanes was ARC-3 or worse, we had a big suitcase of crystals that
we kept in the frequency manager's office.  The flight crew would check
them out when they had to fly to Europe and check them back in at the
end of the mission.  I guess they had to carry someone in the plane who
could retune the ARC-3 when they needed to change frequencies - or maybe
they carried multiple ARC-3 sets to get more pre-tuned frequencies.  I
wasn't in on that part of the operation.