[Elecraft] APF

[Mike K2MK]

I agree with Bill. There's no need to fiddle with the RIT control. I think
Dusty's original suggestion implies that he found the APF to be more
effective at a slightly lower frequency (20Hz lower) than his nominal CW
pitch setting. This may be true but it can be more easily accomplished by
tuning the signal a bit lower in frequency with the main VFO. Then just
tweak the APF center frequency with the SHIFT knob. 

Dusty's suggestion may appeal to some because it doesn't shift your transmit
frequency 20Hz off of zero beat. In the grand scheme, however, 20Hz off of
zero beat is hardly noticeable. 

The important thing here is to play with the APF and learn how to use it.
You don't have to wait for weak signals. You can experiment with medium
strength signals. Then once you get the hang of it you'll be good to go when
trying to pull out a weak one. But don't expect the APF to pull them all in.
The APF has its limitations.

73,
Mike K2MK


Bill W4ZV wrote
> 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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