[R-390] R-390A frequency drift stability specs

[Nick England]

FWIW, maybe it is worth reviewing what the R-390() was designed for - CW
and single channel RATT (RTTY).
CW was, of course, no problem for the R-390() using internal BFO.
The military converted to RATT as fast as it could for a number of reasons,
including the huge benefit of on-line crypto.

Single channel FSK at that time was +/-425 Hz. Using the internal BFO and
AFSK converters, RATT was no problem. Here's a common configuration - Two
R-390A receivers in dual diversity with AFSK converters (AN/URA-8A)
http://www.navy-radio.com/commsta/r390-cv89-01.jpg

For SSB voice the CV-591A converter with crystal "BFO" was commonly used.
Two CV-591A converters were used with RATT on one sideband and voice on the
other sideband (or RATT on both sidebands).
http://www.navy-radio.com/ships/cvs12/hornet-02.jpg

As RATT advanced to multi-channel VFCT, FSK became +/-42.5 Hz with up to 16
channels in a 3kc voice channel. This required AFC in an external converter
driven by the R-390() IF output. CV-116 (twin diversity RATT) and CV-157
(ISB) were both used for this application,
http://www.navy-radio.com/rcvrs/images/frr38-02.JPG
http://www.navy-radio.com/rcvrs/images/frr41-02.JPG
The RATT transmitter signal included a greatly reduced carrier that was
used to drive the AFC, keeping the end-to-end system locked within 1 or 2
Hz forever.

IMHO, the 1950s military HF communication system was one heck of an
engineering marvel.

Cheers,
Nick England K4NYW
www.navy-radio.com