[GreenKeys] AN/SGC-1 Adventure

[wa2hwj at att.net]

ZCZC

The AN/SGC-1 is a late-1940's vintage Navy audio-type RTTY
terminal unit ("converter") which can receive and send with
tones of 500 and 700 HZ (200 HZ shift). I recently resurrected
one of these units as a result of the Paterson, NJ, adventure a few
years ago.  Bob DelGatto and I found the TU and a new
case and panel as we waded through the treasures. Bob recently
presented me with the TU and the panel/case. (He also
gave me a junker unit which became a pile
of parts.) The first order
of business was to put the new panel and case to use by
moving the innards. I cleaned up the dirt and dust, spray
painted the banged-up handles and, after a few hours work, had a
nice-looking unit. Now, of course, does it work? I was
fortunate to have found a manual awhile ago and also
a 1965 RTTY Journal article about the unit (converting for
Ham use; seems that a lot of these were released through
MARS many years ago). I plugged it in and found that it still worked fine, except
for a few burned-out pilot lamps (good old #47's). Applying
500 and 700 HZ tones made it switch between MARK and SPACE,
as shown on the tuning meter. I then removed the 500/700 HZ
discriminator and its associated bandpass filter
and replaced it with two 88 MH toroids and
suitable caps to arrive at a 2125/2975 HZ discriminator, per
the RTTY Journal article. I haven't yet fooled around with
the AFSK tone generator in the unit. The new "discriminator"
worked fine and the almost 60-year old AN/SGC-1 copied
the CFH weather station fine-business. 
If anyone has one of these sitting on the shelf, it might make
a nice weekend project to get it going. The receiving converter
isn't much more complicated than the venerable "Twin Cities TU".
Good old Uncle Sam did an amazing job of refurbising the
front panel: the engraved lettering was filled in and new lettering
was silkscreened over it(!). 
It has a pretty neat automtaic control circuit that allows for
keyboard-operated transmit; just start typing and the unit
goes into "transmit", outputs the AFSK tones and puts
the receiver circuit into standby. Stop typing, and everything
goes back to standby/receive in a three seconds. The AFSK conversion
is nothing more than replacing two capacitors and retuning the
tones to 2125/2975 with a couple of potentiometers on the side panel.  
I plan to add a switch to allow for 170 HZ shift and use this 
boatanchor TU to copy the W1AW bulletins. 
One of these was recently on Ebay for around $30...not a bad price,
except for the fact that it weighs around 40 lbs.

73 to all,
Jack WA2HWJ

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