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World of Ham Radio 1997
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WOHR97_AmSoft_(1997-02-01).iso
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IC-28A and IC-735 Frequency Expansion
WARNING: These modifications are intended for use by those
individuals authorized by MARS/CAP to operate on their
frequencies. Using amateur radio equipment to transmit
outside of the normal HAM bands is otherwise strictly
prohibited by law in most countries.
IC-28A Modification Verified.
D21 on the RF board is connected to the 'BAND' line from
the microprocessor. This line goes HIGH when the frequency
on the display is outside the HAM band. This disables
the final PA. I have added a spdt subminiture slide switch
and a small LED to the top of the case directly above D21
to allow selection/indication of out of band tx enabled.
H.J. Kirchner KI6KD
Icom IC-28 squelch modification
The long, noisy squelch-tail of the Icom IC-28 (A or H model) 2-meter
transceiver can be shortened by replacing C110 (4.7 uf) with a smaller
value (0.1 to 0.47 uf). (I can't remember the source of this
information.)
I put a 0.33 uf in my IC-28H; it's a very worthwhile modification.
The capacitor is on the bottom board (the one with the lithium
battery), just southeast of IC4 as you face the front of the upside-
down radio. The only difficult part is finding the right p-c pads to
desolder on the back of the board.
To remove the board: Remove bottom plate, unplug speaker. Unplug
coaxial antenna connector (gray wire). Other connectors may remain in
place. Remove 5 mounting screws, one in each corner and one near
center. Tilt the board out of the radio. The button in the upper
left corner is CPU reset; you may have to reprogram the memories if it
is pressed. Remember that, although the radio is off, parts of the
circuit are still "hot" because of the memory-backup battery, so be
careful not to short any part of the board during the modification.
--
Frank W9MKV
Note: I haven't tried this, proceed at your own risk! WA2ISE