[Milsurplus] Prc-6 frequency stability

[Mike Morrow]

> I have a prc-6 that no matter how many times I bring it on freq it likes to
> drift. Today testing it I had it drift up to 51.16. Also it would drift
> down to 51.1. Also radio is rocked for 51.000.

Ho did you align it?  The ID-292*/PRC-6 is probably the quickest way, but
all except the earliest manuals tell how to do it with a multimeter.

As John/K9WT said, there is almost *no* probability of the crystal being the
problem.  The discriminator adjustment actually winds up setting the frequency
of the transmitter through the crystal-controlled receiver and transmitter AFC
circuitry.  Any problems in that circuit may cause transmitter frequency control
problems.  I recommend the 1955 Operator ( http://www.ebay.com/itm/350269043938 )
and Maintenance ( http://www.ebay.com/itm/350277705874 ) manuals if you don't
already have them.  The ID-292*/PRC-6 alignment meter shows up on ebay fairly
frequently, or might be available from someone on this list.  I'm sure you
know that the setting chart in the unit is worthless, and is meant only as
starting points for the alignment using the ID-292.

That said, I've played around with several AN/PRC-6 units since I got my first
one in 1969 from Navy MARS.  I've never had any problems that were not the result
of mis-alignment.  My current favorite is an RT-196A/PRC-6 that was re-labeled
in Hebrew by the Israelis.  It has a few replacement non-US parts.  I use a
small DC-DC supply module purchased from Italy, fed by a 6.3 vdc SLA battery
( http://www.ebay.com/itm/160856820093 ).

I last aligned it about three years ago using an ID-292A/PRC-6, plus a frequency
counter to fine set the frequency.  I tested it last night, and it was still
51.000 MHz at start of transmission.  It then very slowly varied +2.5/-0 kHz
after transmitting for more than a minute continuously.  That's pretty good
stability both in frequency and in long-term retention of alignment, at least
for a 60-year-old 13-tube battery-powered set that was a real wonder of
miniaturization in 1951.

I have tested it over a half-mile distance with a 1978 RT-1113/PRC-68.  (The
RT-1113 squelch does not require 150-Hz tone.  There was good-sounding AF at
both ends, except for a little whine from the modern DC-DC power module that
was heard at the AN/PRC-68.

I last saw the AN/PRC-6 in limited use by the USMC at Little Creek, VA, in 1972.
I remember thinking at the time what obsolete gear the USMC retained in their
inventory.

Mike / KK5F