to turn OFF your transmitter AGC...
Just a couple of comments on AGC, ALC etcetera. It is interesting that
there were ever two different terms for what is essentially the same
thing. My experience has been that ALC has been the terminolgy most
often used when talking about transmitting and recording, and AGC tends
to be the terminology used when talking about receiving. Whatever you
call it the purpose in transmitting or recording is slightly different
than in receiving. In transmitting or recording the goal is to keep
levels below the point where there is distortion. The distortion we are
trying to avoid is usually going to in the final power amplifier stage,
or in recording it will be saturation in the magnetic media in an analog
recording, or going past the limits of the analog to digital converter
in a digital mode. In receiving we are usually trying to keep the audio
output at a fairly uniform level, more for comfort (and safety) of the
listener than to prevent distortion. Either way it is a system to
automatically control the level, by automatically controlling the gain
of some stage. So either terminology is correct.There are differences in
time constants and amount of compression, but they are both doing
essentially the same thing. It is interesting to note that in many
"digital" systems the encoding (onto an RF carrier) scheme has
information contained in both the amplitude and phase of the signal. So
information will be lost if AGC or ALC is used improperly. This is
somewhat counterintuitive, since we think of digital as either 1 or 0,
on or off, without need for analog style inbetween levels. Old FM
microwave systems with analog multiplex used class C RF PAs and limiting
in the IF of the receivers. New digital microwave systems use linear RF
PAs, and AGC not limiting in the receiver.
Ken N6KB
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