Re: ALC implementation

Posted by Wes Stewart-2 on Jul 12, 2019; 11:11pm
URL: http://elecraft.85.s1.nabble.com/ALC-implementation-tp7653437p7653769.html

Actually, gain compression reduces "gain" not dynamic range.  All signals are
reduced in amplitude by the same number of dB.  This is the only way it doesn't
introduce distortion.

This reminds me of the endless discussions about RX AGC where everyone has their
favorite combination of rf-gain, threshold, slope, etc, that somehow magically
reduces strong signals while allowing weaker ones to "pop out of the noise."  If
you have one of these receivers, you best only use it for FM reception.

There is nothing inherently wrong with using compression, i.e. ALC on digital
modes if the time constants are appropriate.  I have just run some tests on my
K3S on FT8 while looking at the spectrum on a spectrum analyzer and listening
with a second K3 for the dreaded in-band harmonics while "overdriving" the audio
into the ALC region. With the present setup, I got the "recommended" 4-5 bars
with the Line In at about 7 to 8.  Cranking it up to 30 and maxing out the ALC
at 8 bars made no difference in detectable in-band harmonics, even using a 300
Hz offset. (Split was off)

It's funny that this guy, https://www.youtube.com/watch?v=smWp0TOEtlQ decides
that speech processing has no undesired effects yet is adamant that ALC should
not be used.

Wes  N7WS



On 7/12/2019 2:41 PM, Bob McGraw K4TAX wrote:

> Don't confuse compression and clipping.   Compression reduces dynamic range while clipping sets a hard ceiling and does generate distortion.  Compression used correctly does not generate distortion.
>
> 73
> Bob, K4TAX
>
>
> Sent from my iPhone
>
>> On Jul 12, 2019, at 4:00 PM, Wes <[hidden email]> wrote:
>>
>> What distortion?
>>
>>> On 7/12/2019 1:15 PM, Jim Rhodes wrote:
>>> Nothing when it is done correctly on a mode that can stand the distortion. I personally won't use it on digital modes as my rigs tend to turn it off by default.
>>>
>>> Jim Rhodes
>>> K0XU
>>>
>>> On Fri, Jul 12, 2019, 15:10 Wes <[hidden email] <mailto:[hidden email]>> wrote:
>>>
>>>     And what exactly is the problem with compression?  It's used all over the
>>>     place.
>>>
>>>     Wes  N7WS
>>>
>>>     On 6/28/2019 11:38 AM, Brian Denley wrote:
>>>     > I have always thought that ALC is not appropriate for power control.
>>>     It’s a protection system.  Over use of ALC acts like compression.  No?
>>>     >
>>>     > Brian
>>>     > KB1VBF
>>>     > Sent from my iPad
>>>
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