MICOR

Some time ago, I sent out a message to NET9K6 wondering if anyone had
found a way to modify a Motorola MICOR (UHF) for 9600 operation.  No one
had, but several folks wanted to know if it turned out to workable.
Well, It is!

    With thanks to Dan, N7MRP, who implemented the mods and tested them
out, here it is:

  First, the MICOR was modified for "stand alone" operation (without a
control head) - on P901 (the big connector in the front), pin 11 is
jumpered to pin 1 (Gnd), pins 8,3 & 22 are connected together and to a
2amp fuse connected to the big A+ feedthru going into the PA.  All these
jumpers are done on the control(interconnect) board, except for mounting
the fuse itself.  Unless you want speaker audio to listen to, there is
no need to install volume or squelch pots, and the audio amps are not
used in this application.

  Second, we did a couple mods that seem to help prevent problems before
they arise: add a capacitor (at least 20 microfarads, I use 220 uf)
across C903 on the control board (this is the tubular electrolytic
located just to the rear of the 9.6v regulator transistor heatsink). Add
a diode (1N4001 or better) from P901 pin 16 to any of the A+ pins
(3,8,18), with the banded end to the A+ pin.  (this is a "spike"
suppression diode)

  Third, one mod on the Audio/Squelch board: replace C203 with a 1-10uf
electrolytic/tantalum- I recommend at least a 20v rating.  This improves
the low frequency end of discriminator audio.
CONTINUED IN MICOR.1