[Elecraft] K2 APF implementation?

[Bill W4ZV]

Ron D'Eau Claire wrote:
> 
> Jeff, I have compared the K3's APF with the filter offered in Elecraft's
> AF-1 Active Filter mini-module kit. There is no difference I can hear in
> the
> performance. Actually the AF-1 has more flexibility since you have two
> levels of "Q" to choose from, variable gain, and an independent variable
> low-pass filter function.
> 

Ron, when I read this I didn't think it sounded like the KAF2 I have, so I
checked the manual (you wrote it?)  Per the specifications:

BPF Bandwidth:  80 Hz @ -3 dB; 270 Hz @ -20 dB
Gain:  0-1 dB in OFF (LPF only) and AF1 (first CW filter stage) modes,
slightly higher in AF2 mode (both stages).

Contrast this to the K3's APF:

BPF with 30 Hz @ -3 dB and gain of +9 dB.

http://sites.google.com/site/ft1000apf/w6lxanalysisoftheapfcircuitintheft-1000
(see Slide #3)

The KAF2 is a typical audio bandpass filter like those found in many rigs
(e.g. TS-930S, etc).  The K3 APF is an entirely different animal based on
the FT-1000D's highly acclaimed APF.  I've never found the KAF2 to be very
effective but the K3's can be quite effective in certain cases (but not
all).

73,  Bill





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