[Heath] Controlled-Carrier and audio quality.

[Kenneth G. Gordon]

On 26 May 2018 at 12:46, ChrisIwata via Heath wrote:

> Chuck
> 
> I did some research, and looks like you're right.
> 
> With suppressed (reduced) carrier DSB the carrier level stays the same
> with modulation.  Unbalancing the balanced modulator in a side band
> scheme doesn't imply the carrier goes up with the modulation. 
>
> 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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