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 <[email protected]> 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: [email protected] > [mailto:[email protected]] On Behalf Of Wayne Burdick > Sent: Wednesday, November 03, 2010 7:01 PM > To: [email protected] > 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, [email protected] wrote: > >> Elecraft continues to delight. >> >> FINE tuning ON can be very helpful on really really weak signals >> with the APF. > > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
