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 @ KA6HMG.AZ,USA.NA
EOM
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