[Elecraft] APF

[Bill W4ZV]

IMHO K3WC's APF suggestion is WAY TOO COMPLICATED.  I use APF virtually all
the time and never use RIT, SHIFT, etc.  Just HOLD DUAL PB to actuate APF
and use the VFO to zero beat.  COARSE (10 Hz) VFO steps is usually close
enough but you can switch to FINE (1 Hz) if necessary for ultra weak
signals.  I also strongly endorse N6KR's suggestion below:

"I suggest setting the passband width to about 250-300 Hz when using APF."

This is extremely important since bandwidths too narrow will introduce
additional ringing to the APF which already borders on ringing.  I actually
use a 200 Hz XFIL but set to actuate at DSP 400 Hz.  With WIDTH set to 400
Hz, the signal first goes through the relatively broad (4.0 shape factor)
200 Hz XFIL, then a 400 Hz DSP and finally the narrow APF.  This makes the
cascaded XFIL/DSP look more like 250 Hz, reduces ringing, still allows you
to hear off-frequency callers (although attenuated) and helps your ears
discriminate weak signals from noise by providing a wider background sample
of noise.

73,  Bill  W4ZV





Scott Monks wrote
> Sam;
>      Your explanation is really good Sam, but it seems that something
> doesn't follow for me.
> 
> cut...========================
> 
>>Turn on the RIT control (tap the RIT button). Next, lower the RIT 
>>frequency -20 Hz. (You must have CONFIG:PB CTRL in the config menu set 
>>to .01 to move in 10 Hz steps). If your pitch is set to 500 Hz, then the 
>>tone of the CW should now be 480 Hz. Next, turn on the APF by HOLDING 
>>the DUAL PB button. Adjust the APF using the SHIFT Fc Knob (now APF 
>>control). Move the APF down -20 Hz to match the CW signal. Once you have 
>>the signal in the center of the new 480 Hz tone you should hear that the 
>>CW signal pops up about 5 or 6 dB....
>>Ok, I did this, first setting my pitch at 500 Hz, which actually even cut
out some ringing!  I got the station centered, etc., turned RIT down -20,
activated APF, but then the problem began.
> 
> I am not sure what the "SHIFT Fc Knob" is--if it is just the regular
> "Shift-Lo" knob then this doesn't do anything for me when I turn it. Is
> this the right knob?  Do I need something turned on in CONFIG for it to
> work?
> 
> 
> I have had my K3 a little more than 1yr., and I sort of remember that
> MAYBE I could move the passband once at first, but I my be remembering
> bad!
> 
> Thanks for the help.  73
> 
> 
> Scott  
> 
> AA0AA; XE1/AA0AA
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