-----Original Message-----
From: Ian Roberts <itr@nanoteq.co.za>
Cc: amps@contesting.com <amps@contesting.com>
To: <amps@contesting.com>
Date: 17 February 2000 00:37
Subject: Re: SV: [AMPS] RE: ALC
>
>Hans, you've raised a number of interesting points here, please help me
>out..
>
>> To avoid the problem I always try to keep my microphone gain down just
below
>> the point where the ALC starts to show up on the rigs meter in the ALC
>> position. I will still get maximum pep output but a little less
compression
>> from the ALC. Remember the COLLINS rigs that had dual ALC constants? They
>> had a little compression from the ALC too.
>
>1. The "problem" seems to be the rising spike on initial TX. Has it been
>established that this spike is NOT present (even at reduced amplitude)
>if the mic gain is a bit lower (or the RF power level is set lower)?
In my case, I don't see the spike when there is no ALC indication on the
meter.
>2. Does the ALC produce "compression" or simply limit the PEP?
>"Compression" is normally used in the audio stages to boost the low
>audio levels a bit.
If the decay time is long enough, it should be a pep limit.
In the FT990, there is a transistor which discharges a .22uF cap (fast
attack) with a 1M resistor to +ve for slow decay. The high collector
resistor provides nearly all the ALC loop gain. There is .1uF in series with
10k across the 1M, so the fast attack is delayed while this charges - the
loop gain is 100x lower at the beginning of the attack transient. It makes
for cute little spikes....
I have a suspicion that this part of the radio was simply found to work,
rather than properly designed.
Steve
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