RadioBanter - icom ic-t2h tx expand diode 18 removal mods and findings

In article .com,
wrote:

after doing the remove diode 18 on my icom ic-t2h to expand tx i
noticed that my reception in the higher (170mhz and above) was
distorted. i also noticed a marked reduction in transmitting power in
the high frequencies, stations i could reach at 140.20 couldn't be
reached at 172.15, they couldn't reach me either at 172.15 though we
easily could reach each other at 140.20

the low (140-148mhz) seemed to work ok.

i am studying the electrical diagram if i also have to remove the other

diode to improve higher VHF freek reception.

what you guys find out so far?

The fact that you can persuade the radio's synthesizer to tune
frequencies outside of the 2-meter band, does not mean that either the
transmitter or receiver circuitry is necessarily going to work well on
those frequencies. The transmitter circuit is very probably "tuned"
for operation in the 2-meter band, and forcing it to operate outside
of its tuning range will probably result in degraded performance.

The radio almost certainly has a low-pass filter between the RF
module and the antenna. This is necessary in order to keep
the radio's transmitter from emitting spurs or harmonics in
excess of the FCC limits. This filter is likely to "roll off" any
transmissions above the 2-meter band to some extent, and (if it's in
the receive pathway) will probably reduce the received signal
strength as well.

It's even possible that transmitted at such a high frequency might
damage the radio's power amplifier... the amp's likely to be looking
into a severe impedance mismatch and the high SWR might overstress it.

You don't say where you live, but you should be aware that here in the
U.S. it's illegal to transmit outside of the 2-meter band with a radio
modified in this fashion. Google for "Jack Gerritsen" to understand
some of the potential consequences.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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