[GreenKeys] For owners of Dovetron MPC-1000CT/T II demodulators

[Jim Haynes]

If you have one of these containing the "binary bit processor" board
that is shown on drawing 57349B, you have (or you may have) a circuit
board with a trace that shouldn't be there.

After studying the schematic I was suspicious that the threshold voltage
might not be correct under conditions of selective fading when there
is only a single tone being received.  So I put it on the bench to
measure that voltage (output of U11 pin 7) with a single-frequency tone
input.  Well it turned out that the voltage was always zero, instead of
the negative of the signal voltage.  Further investigation showed that
on the bottom side of the board there is a trace between the ends of
R21 and R22, the ends that are toward the center of the board.  This
should not be.  I cut the trace and now the threshold voltage is what
it should be.

Now I'll have to wait for some RTTY signals to test it; but this should
substantially improve performance when there is selective fading.

Jim W6JVE

jhhaynes at earthlink dot net