[ARC5] A discussion on AGC.

Tue May 9 01:03:16 EDT 2017

On 8 May 2017 at 17:04, K5MYJ wrote:

> In these receivers you don't want the BFO and AVC on at the same time!

My point is that that depends on the receiver.

> The BFO will reduce the sensitivity if the AVC if not disabled.

True....in some receivers.

> These receivers were really not designed for CW. They were designed for 
> VOICE by the pilots of WWII airplanes.

All true.

But those do not answer my questions.

All modern rigs use AGC for CW and SSB.

The difference is that AGC voltage is gotten from a part of the circuit which does NOT also 
receive signal from the BFO.

The same thing occurs in certain models of the AN/ARC-5 receivers where the AGC voltage 
is taken from the last IF stage's (12SF7's) diode which is "far enough" from where the BFO is 
injected that it is not effected by the BFO signal.

When the BFO is injected into the same tube where the detector diode is located (12SR7) 
then the BFO's voltage will add to the AGC voltage and desense the receiver.

Ken W7EKB

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