[Elecraft] The APF feature of the K3.

[Bill W4ZV]

APF was discussed extensively in August 2009 (check the archives) including a
simulation of the exact FT-1000D APF analog circuit which I found and sent
to Al W6LX.  Here's Al's simulation which was the model for the K3's DSP
implementation of APF:

http://sites.google.com/site/ft1000apf/w6lxanalysisoftheapfcircuitintheft-1000

If you search online, you can find the FT-1000D Service Manual which has the
analog APF circuit (less the front panel control pot VR8901-2 which is 1k
ohms).  You must use the original resistor values, not those later changed
in a Yaesu service bulletin (to address complaints of peakiness...which in
fact is what makes it work).  Connoisseurs of APF that bought later
"improved" FT-1000Ds quickly discovered its APF was not as effective as the
original and reverted to the original "peaky" design:

http://lists.contesting.com/_topband/2000-03/msg00027.html

73,  Bill
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