MITREK



Subject: MOTOROLA MITREK TO 9600 BAUD MOD.   MOST ALL MAKES



The Motorola Mitrek is one of the BEST radios to use for general amateur

packet at 9600 baud.

This mod will allow 9600 baud packet with the G3RUH type of modems although

other may work as well.

TOOLS AND SUPPLIES NEEDED:



a. Soldering iron

b. Solder

c. Small cutters or a sharp knife or razor

d. 2ea. Small .1uF disk ceramic caps 12vdc or greater.

e. 1ea. 1uF electrolytic non-polorized cap.

f. Manual for your radio



Ok guys and gals!  Get ready to get on 9600 baud packet!



A) Locate the transmit audio amp/splatter section on the transmitter

   section of the schematic.  Locate the ACTIVE SPLATTER FILTER.

   NOTE the last transistor...Q504 on the vhf version..may be different

   number on other bands.

B) Now locate the transmit channel elements.  Locate pin four on channel

   element #1. Do you note, on the drawing, the line going to pin 4 of

   element #1 to the collector of Q504?  This is your direct FM modulator

   input.  Cut this trace at the channel element.

C) Solder one side of the 1uF electrolytic cap to pin 4 of the channel

   element. The other side of the cap is now you modulation input from

   you modem or tnc.  I will let you decide how to run it into the radio.

   Use shielded wire.

D) Install one of the .1uF caps between pin 3 and pin 1 of the channel

   element.

E) Locate pin 11 on J1.  This is the plug on the front of the radio.

   Hook you receive audio there.  The average person will not need

   to make any mods to the receiver.  If you dont have any real good

   test equipement dont make any receiver mods.  IT WILL WORK AOK.

F) Install .1uF cap between pins 1 and 3 on receiver channel element.



   ****YOU ARE NOW DONE****

NOTES:

   The mod was really easy!  You need to make sure that your max deviation

   is 3khz MAX.  Set your TXD to 200 milliseconds at the beginning...txd 20

   on most TNC's. After you are happy, start lowering you txd.  You will

   probably end up with a txd of 7....or 70 milliseconds.

   The caps on the pins of the channel elements really do not effect the

   9600 baud operation.  What they do is reduce the local oscillator leak

   that emits out of these radios about 20 db...VERY VERY IMPORTANT on

   hilltops.

73's de Jim, WA6OFT
EOM

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