[TenTec] Results so far: AGC: ON or OFF Survey

[JAMES T BRANNIGAN]

Partial quote from my Collins manual
"When listening to strong signals, a reduction in background noise under
no-modulation conditions may be obtained by rotating the RF GAIN control
away from the maximum position. "

In the 75S-3B, reducing the RF gain increased the bias on the AGC line.
This had the effect of over riding the AGC voltage fluctuations.  The S
meter reflected this action.
The side tone is obtained from the 32S transmitter and is adjustable
internally in the transmitter or by using the receiver volume control.

Jim

>Most interesting input,  for me,  was a quote from a Collins
>Radio S-line manual,  not sure if each of you saw it,  so here
>is the quote:
>
>"To copy CW with AGC, set R.F.GAIN to maximum and
>adjust A.F.GAIN for desired  level.   If AGC action is not
>desired, reduce R.F.GAIN setting until S-meter  does not
>kick with signals, and leave A.F.GAIN set as above.   This
>method of  operating results in optimum signal- to- noise
>ratio as well as more pleasing   sidetone level.   The practice
>of operating with A.F.GAIN at maximum and  adjusting
>R.F.GAIN will degrade signal- to- noise performance of the
>receiver."
>
>Note:  I do not know if the above is the exact  text from the
>Collins manual;  and,  I changed "avc" which was in the text
>I rcv'd  to AGC,  just for consistency in our discussion.
>
>Now,  I find the above Collins bit to be unclear!!  In the
>second sentence,  they do not say to turn OFF the AGC,
>just to turn down the RF gain until the S-meter does not
>"kick".  Does that "defeat" the Collins AGC action?  And,
>"leave AF Gain set as above",  does that mean set to
>comfotable listening level,  or set someplace in particular,
>such as exactly where it was when the AGC was on,  and
>the RF GAIN was at full on?
>
>Whatever is meant,  Collins engineers seem to say this
>arrainges things for "optimum" signal to noise,  and
>most pleasing sidetone level (sound volume,  I guess).
>Really does seem to be saying to leave the audio gain
>right where it was set when the AGC was on,  and the
>RF gain was full up.
>
>Anybody able to offer clarification on how the S-line
>actually was used by those in the know back then??
>
>Thanks again,  and 73,  Jim,  KH7M



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