[ARC5] R-25/ARC-5 Stabilized Receiver

[Gordon White]

  There was a continuing problem in the ETO of receivers (maybe 
transmitters) getting off-frequency. A.R.C. sent several engineers over 
to see why and they decided it was the pilots trying to tune the 
receivers while on a mission. Maybe they couldn't get reception and they 
twisted the crank trying to find a station. Anyway, according to people 
(now long-dead) I spoke to  in the 1960s, the decision was not to allow 
pilots to do any tuning. There was also some evidence that  the tuning 
cables introduced some creep from temperature changes, vibration, etc.

    The communications receivers were all designed to be lock-tuned. 
Since I have three early AN/ARC-5 receivers, R-20, R-21 and R-22 (1.5-3, 
3-6, 6-9.c mc) that have the circled S mark, I have to feel that the 
stabilized receivers were part of the change from ARA to AN/ARC-5. The 
standard ARC-5 commo receivers, R-25, R-26, R-27  are all marked with 
the "S"

    The changes were primarily to the variable tuning capacitor. If you 
look at a capacitor from a stabilized receiver the design of the  shaft 
bearing is different. The specs of the trimmer capacitors was changed 
along with various padders, resistors, etc.  I think the alloy of the 
frame was changed, anyway, a number of changes to make the receivers 
more stable, temperature and altitude-compensated. Remember, 
temperatures ranged from planes sitting in the African sun to 40,000 
feet over northern Germany in January.

> The receivers were tuned on the ground using A.R.C's OA-4 Crystal 
> Frequency Generator.


> - Gordon White