[GreenKeys] FW: Seeking Information/Manual on Frederick Electronics 1280 Demod

[David I. Emery]

On Sun, Dec 09, 2007 at 05:33:24PM -0800, William Bytheway wrote:
> Name here is Jim Sanders, W4HSA, and I am seeking info or manual on a
> Plantronics Frederick Electronics 1280 Dual Demodulator FSK RTTY unit I
> recently purchased in new condx from a guy on EBay. I know Frederick went
> under some time ago, but was hoping you might know someone or 
> some place that could hook me up with a manual, or xerox of a manual for
> this unit. It carries a Fscm of 15230 and a Part Number of D5679-2 in
> addition to the Model Number 1280.

	I have a manual I bought from Plantronics some years ago.   At
that time manuals were available from Plantronics, not sure if the
company still exists or still sells manuals for the 1280...

	I don't have a sheet fed scanner, so creating a .pdf would
involve a trip to a Kinkos or Copy Cop place (and maybe some copyright
issues if the company still exists and sells the manual)....

	The 1280/1280As are circa mid to late 80s IC based
superhetrodyne type TUs with switched capacitor tone filters.   As they
are upconverting superhets both mark and space channels can be tuned
anywhere from 300-6000 Hz...  in .5 Hz steps if I remember right. They
include the Fredrick patent ATC threshold correction and will do both AM
(limiterless) and FM (limiter) mode and copy on only one tone.

	They also can be strapped for dual diversity with two demod
boards (the chassis has a controller board and slots for either two AFSK
transmit or FSK receive boards or a pair of receive and transmit
boards). Sounds like you may have the dual receive board configuration
which can be used as two independent TUs or a dual diversity single TU.

	And they are RS-232 controllable with a rather simple and
primitive protocol that talks to a little micro on the controller board.
Thus you can set mark and space frequencies and baud rate from a PC.

	Also they incorporate a software PLL implemented in the onboard
micro which allows them to be used to recover bit timing on isochronous 
bit streams and do optimum integrate and dump filtering per bit.   This
means they can input a stream of bits to a host... rather than requiring
the host to do this with its own software PLL and sampling.

	And they have variable cutoff freq switched capacitor low pass
filtering after the tone  channels - bandwidth set up as is the mark and
space tone filter bandwidth by specifying the baud rate of the signal
either via the RS-232 control path or from the membrane keypad.   The
1280A version will copy up to 1200 baud FSK/AFSK so there is quite range
of filter bandwidths available... ranging down to under 30 baud...

	Input (and AFSK output) is 600 ohm 0 dbm or so balanced audio,
and the data output (and input)  and RS-232 control is standard
Mil-188/RS-232 signal levels plus a couple of other signals like key the
AFSK tone and I think a carrier detect...   RS-232 control is 8 bit
ASCII at various selectable baud rates up to around 9600...

	There have been a few of things released with a high level 20/60
MA tempested interface on the back (with the fancy connectors and
shielding) - this is an add on board that connects to the RS-232 level
stuff... I think with an external loop supply...

	And finally the approximately 16 KHz IF for the mark and space
channels are available on the back panel for hooking up to a XY display
or scope in XY mode for the classic cross type tuning  indicator.

	I have seen the units various places, at Dayton, on Ebay and
elsewhere but haven't heard much about how serious folks find they
compare performance wise with the Dovetron's that are superficially
similar.   I've not read reports of greenkey type folks actually using
them... they are a bit forbidding with a whole bunch of terminals to
connect signals to without many labels as to what they are...

	The ones I have in my barn are NSA surplus from their markings..

-- 
  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."