[Elecraft] K3 APF FINE Tuning

[Guy Olinger K2AV]

This occurs in running in a contest, where you have positioned the
hard skirts of roofing and regular DSP, to keep out the strong
stations just above and just below.  A weak station down in the noise
calls you slightly up or down, but not out of your running passband.
If you tune the RX frequency up or down to bring him into a fixed
center passband APF, then you let one of the strong stations up or
down under the roofing filter and it will start pumping AGC and trash
the weak signal.  Tuning on the APF and tuning its obvious audio
center up or down, without moving the RX frequency, to the remembered
frequency of the weak signal, peaks him right up without letting the
up and down QRM under the roofing filter.  Also it is easier to
remember the audio tone of the weak signal if it fades and move the
APF peak, than tune the RX and hold the audio peak constant.  Unless
you know in your head that you have only tuned 70 Hz of the 110 off
frequency, and have a calibrated feel to the knob, you can't move the
RX and APF peak to where the station was when it sank under the noise.

73, Guy.

On Wed, Nov 3, 2010 at 10:59 PM, Ron D'Eau Claire <ron at cobi.biz> wrote:
> I'm not clear on the value of changing the APF center frequency
> independently of the actual signal center frequency. If the other station
> drifts off-frequency, I just tune him back in with the RIT or, since I use
> SPLIT as my basic operating mode, with the VFO knob.
>
> In what circumstances if tuning the APF frequency useful?
>
> Ron
>
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Wayne Burdick
> Sent: Wednesday, November 03, 2010 7:01 PM
> To: wb6rse1 at mac.com
> Cc: Elecraft Reflector
> Subject: Re: [Elecraft] K3 APF FINE Tuning
>
> Yes, you can fine-tune (1 Hz) using either the VFO or RIT.
>
> In addition, it looks like the next release may provide 5-Hz
> increments for tuning the APF center frequency (presently 10). We're
> testing that now.
>
> 73,
> Wayne
> N6KR
>
> On Nov 3, 2010, at 6:30 PM, wb6rse1 at mac.com wrote:
>
>> Elecraft continues to delight.
>>
>> FINE tuning ON can be very helpful on really really weak signals
>> with the APF.
>
>
>
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