[Elecraft] K3: honest question re Audio Peak Filter

[Bill W4ZV]

Steve Ellington wrote:
> 
> After filtering the cw signal down to 50hz and you kick in an audio filter 
> that has 10db or gain, your jaw drops, your eyes glaze over and you 
> immediately start slobbering about how signals POP OUT OF THE NOISE.
> 

I've never had an FT-1000D but I know some who do swear by the APF.  We had
a previous thread about this which resulted in a circuit simulation analysis
by Al W6LX.  This is using the **EXACT** circuit in the FT-1000D which I
found sent to Al.  Al's analysis is below (in PowerPoint):

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

You can see the APF has a 6 dB BW of ~50 Hz and ~8.5 dB gain.  So how do I
emulate that in the K3?  I have both the 500 Hz 8-pole and 200 Hz 5-pole
filters in my main RX.  Normally I set the filter gain to 1 dB for the 500
and 2 dB for the 200, based on Wayne's recommendations.  However, you can
emulate the APF by setting the gain for the 200 Hz to 8 dB.  Now my rig
transitions from 1 dB to 8 dB gain as I go to 200 Hz BW or lower, and I have
~7 dB gain over the 500 Hz filter at DSP BW = 50 Hz, which is very close to
the FT-1000D APF's characteristics.  

By pure coincidence I had my rig set to 1822.5 as I was doing this.  Lo and
behold, at 2:45 PM here I just heard G3FPQ very weak here at 2.5 hours
before sunset.  Indeed this emulated APF did seem to help, but I'm going to
do much more listening before I draw any conclusions.  If you have a 200 Hz
filter, you might want to give this a try.

73,  Bill


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