This fellow seems to have a good handle on the ALC issue as it relates
to overshoot in the transceiver.
https://www.w8ji.com/alc_exciter_power_overshoot.htm
Here Tom goes into the discussion of good ALC vs. bad ALC systems.
https://www.w8ji.com/ameritron_alc_adjustment.htm
73
Bob, K4TAX
On 2/28/2019 8:51 PM, K9MA wrote:
Many years ago, I built a tube amplifier with what I thought was a
fairly sophisticated ALC circuit. I could never get the ALC loop to be
stable. I know a lot more about control systems now, but I still don't
know how to get ALC around an amplifier to work, and apparently
neither does anyone else. What I don't understand is why it's so hard
with an external amplifier, as every transmitter has ALC for its
internal 100 W amplifier, and that works fine. Why the same design
doesn't work with an external amplifier is the mystery.
The problem with just limiting the drive power and using the
transmitter's ALC is that, especially for solid state amplifiers, the
required drive power can vary considerably with SWR and temperature.
That requires either riding the power control continuously or running
your amplifier well below rated output most of the time. (Unless, of
course, you're running a 2.5 kW amplifier, but that kind of margin is
expensive.) So, if anyone could figure out how to get ALC to really
work with an amplifier, I think that would be worth paying extra for.
73,
Scott K9MA
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