[Elecraft] The APF feature of the K3.

[Geoffrey Mackenzie-Kennedy]

Hi Vic,

Do you know if any plot of the frequency response K3's APF exists, or any 
similar data about its bandwidth at different levels of attenuation, and is 
its response "peaky"?

I might have told you that as part of the ongoing development of my MkII 
H-Mode receiver, I have for some time been considering various additions to 
its audio circuitry - one of which is some form of APF.  The use of DSP is 
not an option for this receiver, because any ADC that I can afford would 
most likely ruin the 110db+  in-passband dynamic range of this receiver. Nor 
is any form of Q-Multiplier

It has struck me though that an Audio Bandpass filter, whose bandwidth at 
the 1db points is say a few Hz without a "peaky" response, might possibly be 
a useful device to use as an APF rather than a filter whose response is 
"peaky" -  when digging out signals in the noise floor. This is speculation 
because I have not yet had the time to build and evaluate the performance of 
an AF bandpass filter for this application.

73,

Geoff
GM4ESD