> >On Monday 15 April 2002 06:41, Peter Chadwick wrote:
> >> Rich said:
> >> >- Mo' ALC-meter indication is seemingly not mo' betta.
> >>
We speak of ALC causing the problem - but ALC simply allows the problem to
occur. The real problem is "flat-topping" during the instant of the first
pulse - prior to ALC shutting down the amplifier state (whether internal or
external).
If, for example, we build an amplifier that runs 10 kw output cleanly and
then use ALC to limit the power output to 1.5 kw output, I believe we would
be in compliance with the FCC rules, even though an original pulse may
exceed 1.5 kw output prior to the ALC taking effect.
The problem with ALC is that there is a slight delay between speech pulse
and application to shut down the amplifier. If that delay occurs after the
pulse occuring in the amplifier, the amplifier will be overloaded and
"flat-top". Although the pulse is "immediately" shut off, it is like
closing the gate after the horse has bolted out.
I believe ALC can be used safely only if the peak output without the
application of ALC is distortion free. If there is distortion, the ALC
will not cure the problem.
I understand there are some rigs that use ALC to turn the power down. So
if you use a 100 watt exciter and crank the output down to 30 watts to
drive the final, you may still have 100 watts output for a instant. If
this output causes overdrive of the amplifier, the splatter must occur.
But if the amplifier is truly linear and has a clean output when driven by
100 watts (5 kw), then the splatter should not occur.
Which is why we build amplifiers that run 5 kw output - so we can use ALC.
73, Colin K7FM
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