[Elecraft] AGC with PSK31 (was: DSP Unit and PSK31 and other digital modes)

[Don Wilhelm]

Bob and all,

I do have a cure for AGC pumping situations - simply turn the AF gain knob
full CW and use the RF gain control to control the audio output level.   I
highly recommend operating  that way at any time a wide IF filter is for
reception of narrow band signals - such as digital modes and CW with a wide
IF filter selected.  This works with or without a DSP unit installed.

The big advantage is that one can hear (for PSK = 'see') signals that are
'down in the noise level' and would normally be obscured by the higher level
signals within the IF filter passband.

I do not turn the AGC off - on the K2, reducing the RF gain does the same
thing as increasing the AGC threshold, so there is some AGC action left
available - the amount of AGC depends on just how far the RF gain is
reduced.

One down side is that the S-meter is no longer calibrated - but one usually
doesn't use the S-meter on PSK31 anyway.  On CW there may be the additional
concern that you can tune across a very strong signal and not have full AGC
action, but this rarely occurs for me - there is usually time to reduce the
RF gain even further while the strong signal is down on the filter slope.
----- Original Message ----- 

  The issue with using narrow audio filters
> is the AGC level before the audio filter sets the level of the
> signal following the filter unless this is compensated for in
> the DSP audio filter.  You would see this is a strong signal inside
> your IF bandwidth, set by the K2 IF filters, resulting in a
> pumping of the level of the signal coming out of the KDSP2 audio
> filter.
>