I am working on developing a faster acting ALC. Since the voltage developed
by the amplifier, and the response by the transmitter is not fast enough in
many combinations to shut down the transmitter, a different direction is
needed.
The foolproof approach is as follows: first, attach a potentiometer to the
alc input with 12 volts across it. Gradually increase the voltage developed
to determine how much voltage is needed to shut down the transmitter.
Once that voltage is determined, set up a potentiometer with a sufficient
voltage across it, so that a 15 degree rotation will shut down the rig. For
safety purposes, install diodes across the adjustable leg to ground to
assure that a higher voltage will not be impressed upon the ALC input.
Also, be sure to install a series resistor in series with the pot to limit
current.
Then, attach a 2" arm to the pot rotor and a 2" arm to the pot body.
Install a spring from an old ball point pen between these two arms to force
the two arms apart.
Then, install this pot on the end of a boom microphone. Insert the two arms
into the mouth so that when your mouth is closed, the voltage is zero, and
as your mouth opens, the voltage increases to maximum alc voltage. A little
trial and error is required. As you speak, the ALC voltage will be
developed before the words come out - and shut down the rig before the
overdrive.
Be careful to insulate all voltages from the arm.
This technique is not recommended for AC-DC type transmitters. It has been
found that this approach works correctly, even with 25 cycle power lines.
Colin K7FM
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