[GreenKeys] New subject: another Dovetron crock.

[Jim Haynes]

Recently I reported in the Dovetron MPC1000CR/T II FSK converter that
there is an extraneous PC trace on the "binary bit processor" board
which prevents the threshold corrector from working.  Yet when I cut
the offending trace performance of the whole unit was worse than ever.

Well now I've had time to study that, and found that on the board in
my unit there are two incorrect value resistors in the same area.
R24 and R25 next to U11 on the BBP-100 Mark II board are supposed to
be 10K each and on mine they were 100K.  Which made the threshold five
times as big as the signal instead of half as big.  Now at least I'm
getting output when running the internal dot generator and mistuning
the filters to simulate selective fading.  The signal does get biased
as the tones fade selectively, but at least it doesn't go away.  I'm
still unclear on the purpose of the 400mv offset.

I have two different schematics for this board.  My unit seems to
correspond to the one that is not marked "REV B" under "MARK II"
REV B changes some resistor values around U11 and the values there
seem to make more sense; but the ones that are not "REV B" should
work OK.

Further reports when I have time to do more testing with real signals.

Jim W6JVE


jhhaynes at earthlink dot net