[GreenKeys] Understanding the Dovetron demodulator

[Jim Haynes]

So I got a little deeper into it, somehow.  I started comparing the main
board schematic of the Dovetron MPC1000 (drawing 75103E) with the patent.
They match up pretty closely.  I was looking at the portion of the
circuit shown in Fig. 3 of the patent, where the mark and space signals
are detected alone or combined.  On the schematic it just shows the
outline of ICs where the NAND gates are shown in the patent, and shows
the pin numbers and wiring.  And that part doesn't make any sense at all,
because the pin numbers on the schematic do not correspond with the way
the ICs are built.

So I opened up the unit to see what is going on there, and - those parts
are not in there!  Where Z16 and Z24 would be are the sockets for the
"binary bit processor" daughter board.  Everything downstream of that
is left out until what would be the output of Z36, which comes from
the BBP board.

I don't have a legible copy of the BBP schematic - if someone does I'd
appreciate a scan or a copy.  So I'm at a loss as to how the signals
are processed on that board.  It is apparent that there is a final
low-pass filter with the bandwidth selected by the front panel
narrow-medium-wide switch and by resistor packs plugged into sockets
on the board.

So I presume the kind of signal processing shown in the patent is not in
fact the best way to do it, and that a better way is on the BBP board.



jhhaynes at earthlink dot net