Wayne, I was pleased to see the APF added to the K3, though I think it is not as useful on radios with such good basic filtering, as compared to older radios. OTOH: it's a favorite feature of my old FT1000D! 73, andy ae6y
-----Original Message----- From: Wayne Burdick Sent: Tuesday, June 26, 2012 11:19 AM To: [email protected] Cc: Elecraft Reflector Subject: [Elecraft] K3/KX3 Operating Tip: APF (audio peaking filter) forweak-signal CW work Both the K3 and KX3 have an APF control (audio peaking filter). APF can be extremely effective when you're trying to copy weak CW signals buried in noise. Most DSP filters have very steep skirts; they're often referred to as "brick-wall" filters for this reason. This is the type of filtering associated with the WIDTH control (K3) or PBT control (KX3). In contrast, the APF is a filter with a very narrow peak (about 30 Hz at the -3 dB points) and very broad skirts. The narrow peak brings up the signal amplitude slightly, while the broad skirts prevent noise from being amplified and delayed in such a way as to dominate the signal. The APF function used in the K3 and KX3 is a modern DSP reinterpretation of the hardware APF circuit found on some legacy transceivers, which was very effective. On the KX3, the APF switch is labeled "APF" (tap), while on the K3, it's labeled "DUAL PB" (hold). The K3 actually provides two different special filter functions; use the DUAL PB menu entry to set up the switch for APF. When you turn on APF, the DSP graphic changes to remind you of the nature of APF, with its narrow peak and broad skirts. I suggest setting the passband width to about 250-300 Hz when using APF. The DSP graphic still shows an approximate representation of the width even with APF turned on. 73, Wayne N6KR ______________________________________________________________ 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
