Audio Agc Adjustment - ozQRP MST3 Construction And Operation Manual

13.5 A AGC
UDIO ADJUSTMENT
The audio AGC is easy to set up and the procedure outlined below has been refined after many
hours of on-air listening.

Set the AF gain control to about half way

Inject an S9 RF signal into the antenna connector.

Slowly rotate the AGC trimpot (VR3) clockwise until you can just notice a lowering of the
audio level. This sets the point where AGC starts to operate.

Increase the RF signal level and check that the rate of increase of the audio level is much
less than the RF input level change.
The AF gain control is located before the audio AGC circuit and so adjusting the AF
control for signals above S9 may not have the expected outcome. This is because the
AGC circuit is attempting to adjust the audio and keep it constant. For signals below
S9 the AF gain control works in the expected manner.
If the audio AGC is not required simply rotate VR3 fully counter-clockwise.
MST3 Construction and Operation Manual – Issue 1 Page 54