[Heath] Controlled-Carrier and audio quality.

[ChrisIwata]

Yeah, what you're talking about is the AGC time constant

If vintage AM radios used short AGC time constants to track rapid QSB 
better, than controlled carrier  AM probably sounded like AMBC 
(commercial AM) with lots of QSB.  Those radios weren't very quiet, so 
that amplified the problem.  And back then, everybody was on 80 or 40, 
which have high noise levels anyway

For SSB, the carrier is re-injected at the product detector, so QSB is 
not as noticeable.  Longer AGC time constants are acceptable.

  I often listen to Arnie Corro @ Radio Havana.  If the signal is S3 
with QSB, I'll switch to SSB mode and zero beat.  The copy becomes R4.  
Amazing.  Or, I'll pull out the old Kitchin Regen and set it to just at 
oscillation.  This re-injects the carrier, plus the bandwidth is really 
decreased.  Both help to get good copy.   I don't have a radio with DSP

Unless the ITU updated their classifications for radio emissions, there 
is no classification for controlled carrier AM.  AMBC is A3E, SSB is J3E

Chris


On 5/26/2018 1:44 PM, Kenneth G. Gordon wrote:
> On 26 May 2018 at 12:46, ChrisIwata via Heath wrote:
>
>> With controlled carrier AM the carrier rises with the modulation.  But
>> unless well designed, not linearly.
>>
>> Still, I think I was right about saying both can be demodulated with
>> an envelope (AM) detector.  However, I've read that if the AM receiver
>> uses AGC,  carrier controlled AM usually sounds bad
> Well, that depends, greatly, on what exactly you mean by "bad". The audio quality from a
> controlled-carrier AM rig can sound very good. I know my old DX-35 sounded very good,
> since once a fellow ham recorded my transmission and then played it back to me.
>
> However, what makes, or made it, undesirable to most AM operators at the time was that
> the usual AGC systems of the time had very short "hang" times. This means that the
> background noise would very seriously intrude on what the receiving operator was trying to
> hear.
>
> I.e., the background noise would rise very high at the times when the carrier from the CC
> transmitter was "low" or weak, then when the audio came back up when the CC operator
> would speak, that would suppress the noise.
>
> Modern rigs, with their "hang" AGC systems, which work very well for SSB signals, would
> NOT have this problem.
>
> Do you understand what I am trying to tell you? I am not sure I have made it clear from what
> I have said above.
>
> Do remember that the AGC systems of the OLD days depended on the carrier to "set" the
> receiver's sensistivity. When there is no, or too low, carrier level, the background noise rises
> way up making the received signal SOUND noisy, when it really isn't.
>
> Ken W7EKB
>
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