K3 CW Filter
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I'm just setting up a new K3 (4657), and the 400 Hz 8-pole CW filter (KFL3A-400) seems to have a significant offset. The 6 dB audio bandwidth (AGC off, internal dBV meter) was 236 Hz, and the center about 100 Hz below the sidetone/CWT. Setting the offset for that filter to -0.13 put the center frequency within 2 Hz of the sidetone, but only increased the audio bandwidth to 316 Hz. (ARRL measured 341 for that filter.) Since the audio bandwidth is still low, I'm guessing the filter bandwidth is less than 400 Hz, in addition to having an offset.
Any comments or suggestions before I bother Elecraft support? 73, Scott K9MA ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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It is quite normal for there to be offset in the 8-pole filters. I
have three, and they all do. Enter the offsets and be happy. 73, Jim K9YC On 9/25/2010 9:17 AM, SCOTT D ELLINGTON wrote: > I'm just setting up a new K3 (4657), and the 400 Hz 8-pole CW filter (KFL3A-400) seems to have a significant offset. The 6 dB audio bandwidth (AGC off, internal dBV meter) was 236 Hz, and the center about 100 Hz below the sidetone/CWT. Setting the offset for that filter to -0.13 put the center frequency within 2 Hz of the sidetone, but only increased the audio bandwidth to 316 Hz. (ARRL measured 341 for that filter.) Since the audio bandwidth is still low, I'm guessing the filter bandwidth is less than 400 Hz, in addition to having an offset. > > Any comments or suggestions before I bother Elecraft support? > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Make sure you're not trying to measure the 400 filter offsets with the DSP
set to 400. To measure the filter offset correctly, first define the filter "too wide" in the K3 utility. Eg define the 400 filter as if it were 1.4. Then use a high PITCH setting of 700 to make sure that audio rolloff is not in play. Make sure that MENU:RX EQ settings are all at zero. Be sure the AGC is OFF for your measurements and use ATT. Adj SHIFT until the FC value shows a *0.70. Set WIDTH to 1.20. Now measure your 6 dB points. Average the two, and offset the filter by that amount. RECHECK and readjust for any leftover. In my case, to align the roofer rejection skirts to match DSP skirts and get max dive on the skirts, I use -30 dB points to set offsets rather than -6 dB points. For me the roofers are all about the steepest possible skirts for rejection. The best matching DSP setting is the one (after setting offset) that when you narrow it up changes the -30 to -60. When I've done that THEN I measure the -6 dB points and that is my best aligned operating bandwidth for that filter. Add 50 Hz to that WIDTH setting and use that as the filter width definition in the K3 utility. This gives me both a "loose" and "tight" setting for that roofing filter. 73, Guy. On Sat, Sep 25, 2010 at 1:03 PM, Jim Brown <[hidden email]>wrote: > It is quite normal for there to be offset in the 8-pole filters. I > have three, and they all do. Enter the offsets and be happy. > > 73, Jim K9YC > > On 9/25/2010 9:17 AM, SCOTT D ELLINGTON wrote: > > I'm just setting up a new K3 (4657), and the 400 Hz 8-pole CW filter > (KFL3A-400) seems to have a significant offset. The 6 dB audio bandwidth > (AGC off, internal dBV meter) was 236 Hz, and the center about 100 Hz below > the sidetone/CWT. Setting the offset for that filter to -0.13 put the > center frequency within 2 Hz of the sidetone, but only increased the audio > bandwidth to 316 Hz. (ARRL measured 341 for that filter.) Since the > audio bandwidth is still low, I'm guessing the filter bandwidth is less than > 400 Hz, in addition to having an offset. > > > > Any comments or suggestions before I bother Elecraft support? > > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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> Eg define the 400 filter as if it were 1.4. Then use a high PITCH > setting of 700 to make sure that audio rolloff is not in play. Or enable the filter and measure the bandwidth in DATA A. DATA A will center the filter at 1500 Hz and you can make the DSP bandwidth up to 4 KHz. 73, ... Joe, W4TV On 9/25/2010 6:39 PM, Guy Olinger K2AV wrote: > Make sure you're not trying to measure the 400 filter offsets with the DSP > set to 400. To measure the filter offset correctly, first define the filter > "too wide" in the K3 utility. Eg define the 400 filter as if it were 1.4. > Then use a high PITCH setting of 700 to make sure that audio rolloff is not > in play. Make sure that MENU:RX EQ settings are all at zero. Be sure the > AGC is OFF for your measurements and use ATT. Adj SHIFT until the FC value > shows a *0.70. Set WIDTH to 1.20. Now measure your 6 dB points. Average > the two, and offset the filter by that amount. RECHECK and readjust for any > leftover. > > In my case, to align the roofer rejection skirts to match DSP skirts and get > max dive on the skirts, I use -30 dB points to set offsets rather than -6 dB > points. For me the roofers are all about the steepest possible skirts for > rejection. The best matching DSP setting is the one (after setting offset) > that when you narrow it up changes the -30 to -60. When I've done that THEN > I measure the -6 dB points and that is my best aligned operating bandwidth > for that filter. Add 50 Hz to that WIDTH setting and use that as the filter > width definition in the K3 utility. This gives me both a "loose" and > "tight" setting for that roofing filter. > > 73, Guy. > > On Sat, Sep 25, 2010 at 1:03 PM, Jim Brown<[hidden email]>wrote: > >> It is quite normal for there to be offset in the 8-pole filters. I >> have three, and they all do. Enter the offsets and be happy. >> >> 73, Jim K9YC >> >> On 9/25/2010 9:17 AM, SCOTT D ELLINGTON wrote: >>> I'm just setting up a new K3 (4657), and the 400 Hz 8-pole CW filter >> (KFL3A-400) seems to have a significant offset. The 6 dB audio bandwidth >> (AGC off, internal dBV meter) was 236 Hz, and the center about 100 Hz below >> the sidetone/CWT. Setting the offset for that filter to -0.13 put the >> center frequency within 2 Hz of the sidetone, but only increased the audio >> bandwidth to 316 Hz. (ARRL measured 341 for that filter.) Since the >> audio bandwidth is still low, I'm guessing the filter bandwidth is less than >> 400 Hz, in addition to having an offset. >>> >>> Any comments or suggestions before I bother Elecraft support? >>> >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> 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:[hidden email] > > 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:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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