[Milsurplus] Manual for Plantronics HF FSK 1280A modem wanted

[Dave Emery]

	I acquired a couple of Plantronics/Frederick Electronics 1280A
FSK converters (hf fsk modems) a few years ago and recently got
interested in trying to make one work when a friend asked me about them.

	I have never been able to obtain a manual and schematics - does
anyone know where I could find a manual or have one they would be
willing to copy for me for expenses and a profit ?

	The 1280A is a somewhat modular tunable hf fsk modem circa the
mid 80s implemented in through hole analog and digital IC technology
using switched capacitor filters.  It allows independent tuning of both
mark and space frequency in 0.5 hz steps from 300 hz to 6 khz and
supports baud rates from 30 baud to 1200 baud with 6 different filter
bandwidths.   It supports both AM type limiterless detection with
threshold correction and detection on only mark or only space tones.  It
also provides a mark hold squelch function and carrier detection.

	It will support both isochronous operation (synchronous) with a
built in PLL that will lock on a synchronous bit stream and sample and
regenerate the data, and also async start stop operation with sampling
and regeneration of the start stop characters and apparently speed-up
conversion and output of the data over a RS-232 port.   I believe one
can also access the raw detected data unsampled and not re timed.

	It can be remote controlled over a 19.2 kb RS-232 port or from
membrane switches on the front panel and has plasma displays of the mark
and space frequency and baud rate and audio level in both mark and space
channels.

	It also supports 2 channel diversity operation, either
apparently by having two demod boards in one chassis or by tying two
units together via back panel connectors.

	In the configuration I have, the units also include a transmit
board that generates a high quality AFSK signal suitable for input to a
SSB transmitter, so they can be used both to send and receive various HF
FSK formats.

	Audio input and output is the standard balanced 600 ohms of most
professional gear at the usual 0 dbm level.   Tone output level is
adjustable.   Most of the other outputs appear to be RS-232, including
carrier detect and request and clear to send...

	The units I have were probably NSA surplus, and I suspect
generally optimized for high performance HF FSK monitoring.   Certainly
Frederick Electronics was famous for FSK converters for that purpose

-- 
	Dave Emery N1PRE,  die@die.com  DIE Consulting, Weston, Mass. 
PGP fingerprint = 2047/4D7B08D1 DE 6E E1 CC 1F 1D 96 E2  5D 27 BD B0 24 88 C3 18