The RF PA in Omni VI and Paragon rigs do not have "Power Cutback"
circuitry. There is no ALC or reverse power protection circuitry in
these PAs. They are designed to feed a 50 ohm resistive load. If you
connect a 100 ohm resistive load the RF voltage produced by the PA will
be about the same as with a 50 ohm load, and the current supplied will
be about half, resulting about half the RF power delivered to the load.
This is not a problem for the Omni VI, though it may not be enough drive
for your amplifier. If you connect a 25 ohm load, the RF voltage
produced will be about the same and the current will try to be about
double. That would be about double the power produced, and that IS a
problem for the Omni VI PA. Ten-Tec power supplies for these rigs have
current limiting, which protects the PA from over current. If you are
not using a current limiting power supply, you had best do something to
protect your Omni VI or Paragon PA from over current due to low
impedance loads. This is why there are frequent discussions about where
to get fast acting (Airpax for example) circuit breakers on this reflector.
The power that can be delivered by an Omni VI RF PA is dependent on the
load connected to it, not because of any power cutback circuitry in the
PA though. It will only produce the rated power into a proper load.
This is not the same as with PAs which do have reverse power protection
or ALC circuitry.
DE N6KB
My problem was that the GLA-1000 lacks a tuned input circuit. It was
designed for exciters with tube finals, so input from the exciter is
through a capacitor. This presented varying impedances (not 50 ohm) to
the output of the Omni VI causing it to cut back its power. I could only
get full power out of the amp by using a small tuner between it and the
Omni VI.
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