[GreenKeys] RCA SSB receivers with mechanical AFC

[sdaitch at mor.ibb.gov]

Back in the same time frame, when VOA was heavy into 
HF relay for program material from the Washington studio
complex to the overseas relay stations, we used RCA SSB-3
receivers that had a similar mechanical AFC circuit.

System wide, I suppose there were maybe 150 of them.  I think
there were about 25 in the Kavala receiver site, and Greenville
had 8 at the old receiver site.  I don't know about the other
stations, numbers, that is.  

These receivers were dual diversity, designed as dual diversity, 
all designed by RCA when RCA was heavy into supported point to point
HF systems.  The VFOs in the master osciallator unit, the 400 Unit as
it was called, was made by Collins, 70-E-15, per the parts manual.

There was a sharp 100 kHz filter for the carrier, and that signal
was fed to phase comparison circuit, and if there was any drift in the 
frequency, the error signal went to a driver circuit, driving four
6CL6s, which operated the AFC motor.  The motor was geared to a variable
capacitor across the master oscillator, to bring the receiver back on 
frequency.  

The RCA receiver was two complete racks, although the audio rack
was typically only about half populated in our receivers.  Per the
RCA manuals, the lower half of the rack was populated with generally
16 channel tone pack decoder modules.

73
Sheldon
The R-390As actually used with VFT signals had an outboard tracking demod (a 
> CV-157 if I remember right) that tracked the partially suppressed carrier 
> witha mechanical servo (I kid you not)....
> 
> -- 
>