From: W1OQ@N7MRP.AZ.USA.NA
To  : NET9K6@ALLUS


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.

  If your radio has a CTCSS encode board plugged into the exciter,
remove it.  Install JU304, which is located immediatly adjacent to the
encoder board connection on the exciter.  Depending on which exciter you
have, the encoder will have either 7 or 11 pins - in either case the pin
you will use to inject transmit "audio" is the one adjacent to the big
square hole, towards the outside edge of the radio (pin 6 for 7-pin, or
pin 10 for 11-pin ones).  Connect a shielded lead from this pin to an
unused pin on P901 (I use pin 27).  On the exciter, trace the land from
the pin you just connected to and you will find an 82k resistor -
replace it with a 10k resistor (1/4w) and a 10uf capacitor in series.
(Some exciters already have a 6.8uf cap in series - if you are SURE
yours has the cap, you don't need to add another!

  On the receiver RF/IF board, remove the two crystal filter "cans" that
come after the IF amp IC (Y103 and Y104), and replace them with 1000pf
disc caps (not critical).  Note that the caps DO NOT connect to the
center ground pin!  This mod is CRUCIAL to making the receiver work at
9600!

  Thats ALL there is to it - naturally, you need to tune the radio up,
but I figure you already knew that!  Connect your transmit audio to
whichever pin you connected the jumper to, receive audio (discriminator)
is on pin 20, PTT is pin 16, and 12v goes to the two big pins in the
middle (pins A and B).

  I would advise obtaining a service manual for these radios if you plan
on using them - it is Motorola part # 68P81015E70, and you should be
able to order one through any Motorola service shop.

  73 DE Hartley W1OQ @N7MRP.AZ.USA