For bands below 15m, the K2 sets the VCO so that the LSB image from the first mixer falls within the crystal filter, however for 15m and 10m it uses the USB image (since VCO only goes up to 24MHz or so). When you are in CW mode, you want the baseband to be LSB. This means for 80m-17m, you need to put the BFO below the filter passband, since the output of the 1st mixer is already LSB, but for 15m and 10m the output of the 1st mixer was USB, so you need to flip it by placing the BFO above the filter passband. This is why the perceived offset on NaP3 goes negative for the upper bands. Maybe you remember when you did the CAL FIL procedure, one of the parameters you had to set was in fact the BFO frequency.
Why is there a difference between 20m and 80m-30m? I’m guessing maybe you are using a different filter on 20m, which has a slightly different BFO offset. For 15m and 10m, if you use a different filter, the change in BFO offset will be even more significant, since when you set the width of the filter, it mainly affects the upper edge of the passband, and so the BFO offset must be adjusted to compensate (remembering that for 15m and 10m the BFO is set above the passband rather than below). -- 73 de Matt VK2RQ On 15 novembre 2015 at 3:16:21 AM, K8AC ([email protected]) wrote: I've been using my K2 with LP-Pan and NaP3 for a few months on the lower bands and just recently got on 20 and 15 meter CW with it. I found that the offsets you specify in NaP3 were considerably different on 15, 12 and 10 meters while that for 20M was just a bit off from the lower bands. 17M offset was the same as the lower bands. For example, the global offset required on 80, 40 and 30M is 1170 in my case. For 20M, it's 1200. For 15M it's (-285) and (-330) for 10M. When I say the "offset required", that means the value I need to specify in order for the NaP3 center frequency indicator line to be exactly in the middle of a received CW signal. Not quite sure why the offset difference - obviously the IF signal is not exactly the same for all bands, but why not? -- View this message in context: http://elecraft.365791.n2.nabble.com/K2-and-NaP3-IF-offset-values-tp7610348.html Sent from the Elecraft mailing list archive at Nabble.com. ______________________________________________________________ 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 Message delivered to [email protected] ______________________________________________________________ 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 Message delivered to [email protected]
