Bruce,
Although you can disconnect half of the four final transistors and change
the matching components appropriately to have a 50 watt PA, it's better to
simply exchange the 100W amplifier board for a lower power board. I'm
guessing that you could probably find someone to swap boards with, maybe
even make a few bucks in the deal..
It is not a good idea to reduce either the drive level or the PA supply
voltage to achieve a lower power output, because the PA can become
unstable. A solid-state PA is normally designed to present a stable
source impedance which, in basic terms, is directly proportional to supply
voltage and inversely proportional to PA current. Reducing the drive
level will reduce PA current, thus raising the apparent PA source
impedance and causing a mismatch with the load impedance- usually the
reactive input impedance of a duplexer. This is not good, and is an
invitation to instability. Reducing the supply voltage has the opposite
effect on the apparent PA source impedance.
If you have the requisite test equipment and time, you may be able to
adjust both the drive level and the PA supply voltage to achieve stability
at a lower power output level. This is a lot of work, and may be much
more work than simply replacing the PA board.
73, Eric Lemmon WB6FLY
brucenanney wrote:
> What is the best way to reduce power on a 100 watt micor mobile for
> repeater use? I have reduced the voltage in to 12.8 volts and have
> developed a cooling system on the P.A. deck that has constant air flow
> over the circuit board as well as the the heatsink.
> Thanks, Bruce KD4BOH.
>
>
> Yahoo! Groups Links
>
>
>
>
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