On Tue, Jan 13, 2015 at 11:23 PM, Jim Brown <[email protected]> wrote: > 250 Hz filter set to switch in at 350 Hz, and I do most CW operation with a > 250 Hz IF setting. These are settings you can play with.
With the 8 pole CW filters there is a not so obvious method to the madness here. We do the same thing as Jim with the "250" filter, but here's some more stuff to add to the discussion. The K3 8 pole filters are electrically the same as the 8 MHz IF INRAD filters used in the FT1000MP. They went together with 455 kHz IF filters also called 400 and 250. In series, they produced a 400 and 250 Hz CW overall bandwidth of exceptional sharpness and a combined floor below the noise floor of most measuring instruments. In the K3, the 455 kHz filters are replaced by the K3's DSP, and the 8 MHz filters are now the roofing filters in a different mounting. Wayne chose to retain the FT1000MP nomenclature for the filters, 400 and 250. Used by themselves as they are in the K3, the "400" Hz is really a 440, and the "250" Hz is really a 330 Hz. I switch in the "400" Hz at 450 and the "250" at 350. This is a filter choice and setting adopted by all the K3 "bringers" who operate NY3A multi-op in the CW contests, including N4AF who lives there, and has a pair of K3's. With the 400 and 250 offset tweaked to center them on the DSP passband, the combined passband at 450 and 350 will transform a key click to a spike, which the K3 handles nicely. The K3, with DSB NB set to dSP t2-7 or t3.7, IF NB off, and CONFIG: AGC PLS set to nor, with those filters and width settings one can nearly eliminate key clicks, even from a loud station up or down only 400 Hz. This is contesting-developed information, but it works well in any setting. The roofing filter plus DSP is almost, but not quite as sharp a passband as the MP's cascaded 8MHz/455 kHz filter combo. But it takes a lab instrument to tell the difference, and the K3's DSP and firmware driven features open up a whole new world for contesting beyond the MP series. Before the K3, the MP was THE contesting radio. I would note that in crowded contesting conditions, you pretty much have to use a filter which matches the DSP setting. What gets by the roofing filter can engage the "defensive" hardware AGC which is there to keep input to the analog to digital conversion in the sweet range of the AD device. This can become a problem with very loud signals right at the edge of the DSP passband, if the roofing filter is not close in bandwidth. 73 and good luck, Guy K2AV ______________________________________________________________ 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]
