[Premium-Rx] Watkins Johnson WJ8690A/MCR

[David I. Emery]

On Sun, Jul 04, 2010 at 12:46:49PM +0930, Berndt Josef Wulf wrote:
> G'day,
> 
> I would be grateful for any information on above receiver. 

	It is a early 90s FM, AM, USB, LSB, FSK, CW, DQPSK computer
controlled (no front panel)  VHF/UHF six channel receiver that tunes
from 25-1100 MHz and 1500-2300 MHz in 100 Hz steps. 

	Consists of a 70 MHz IF and controller  box (8690A/MCT) and a
separate dual channel tuner box (8690A/DCT) - with two separate
tuners/70 MHz downconverters in it that allow any two 25 MHz segments of
spectrum (in 1 MHz steps) from 25-1100 MHz to be input to any of the 6
70 MHz channel tuners.

	The individual tuners each have a 25 KHz roofing filter and DSP
based demods (two DSPs per channel) that implement further selectivity
and the actual demodulation of the signal.   Bandwidth ranges from
hundreds of Hz up to 20+ Khz...

	Control of this is via a PC/laptop  using either ethernet or a
serial port...

	Depending on the cards installed audio output is analog or
digital in a couple of formats (T1/E1 and a proprietary WJ parallel bus
are supported, plus SCSI).

	These receivers were originally designed mostly for intercept of
old fashioned (and almost entirely no longer in use) ANALOG FM 
cellphone and INMARSAT traffic, but they are completely general purpose
receivers and can be used for receiving normal NBFM, SSB  and AM signals
in the VHF/UHF spectrum and with some DSP upgrade, also P25 and other
narrow band digital public safety and ham band signals - each receiver
being capable of simultaneously capturing 6 signals all at once.

	Some have shown up on Ebay over the years, but unless you have
BOTH the dual channel tuner box AND the 70 MHz receiver box proper it
isn't a complete system and much less useful.   And there are also
1500-2300 downconverter boxes and preamps and other accessories around
as well.
	
	And a sister repackaged version exists, the 8691A,  which uses
the same modules but all packed into an all in one  mobile version (not
the rack mounted 8690A with two components) with the tuners mounted
inside the main box.

	Very little documentation (and no WJ software) exists in private
hands for these things... but it is possible to make them work as general
purpose VHF/UHF receivers if one is willing to do some reverse engineering.
And analog cell (and INMARSAT) is dead, so there isn't much one can do
with them for that any more.

	The dual channel tuner is actually a respectable low phase noise
high dynamic range external 10 MHz reference 25-1100 MHz to 70 MHz
downconverter BTW... and can be used with other DSP hardware capable of
handling a 70 MHz IF input... 

	There are a few WJ collector types around who have some of these
systems from Ebay - either complete or not... and they are a fairly neat
and somewhat more modern than some WJ radio...

	Subsequent 869x generations converted to VME or VXI cards and fancy
FPGA I and Q demod chips... those, I suspect, are less useful.


-- 
  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."