Topband: Group delay distortion in receiver filters

[Tom Rauch]

> Was the AGC on?  If so, try turning it off.  I know that in some
situations,
> it's not practical to run without AGC, but the AGC is an example of a
> nonlinear system that can convert phase distortion into amplitude
distortion
> through gain modulation.  In my IC-781, the AGC time constant is
> continuously adjustable.  With rough noise I can often improve copy of
weak
> signals by careful adjustment of the AGC.

Hi John,

A time-distortion of ~18mS in the keying sidebands of a CW signal certainly
would have a large effect on the CW sound, as it would on any noise pulses.

Other than group delay, what do you suppose the difference is between the
751's 250Hz  455kHz filters that are terrible for signals in the noise and
the 250 Hz filters in Drakes that are excellent on weak CW, even with
Drake's notoriously poor AGC? The passbands are similar, neither are poorly
shaped so far as cheap mass produced filters go.

73 Tom