K2 CAL_FIL and the BFO
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I'm new to the list, with a couple of questions on the K2. My s/n 6770
has been running for about a week: this weekend put in the KSSB2, KDSP2 and KNB2. When I select from the four CW xtal filter bandwidths, I get a slightly different pitch on the received CW station. Qusetion 1: Is that pitch change directly due to the offset I have dialed in during the filter calibration? The circuit changes the bandwidth of the Cohn crystal filter and, at the same time, I dial in an offset to center that new passband to my desired pitch. So, I'm confused why the pitch changes - maybe it's just calibration error because the tuning step is coarser than my ear. Question 2 is an observation: CW mode is LSB all the way to 17 meters, then USB from 15M up. This is normal, right? On previous (upconverting) radios it's always been USB from 20M up, so this surprised me. Thanks for any help with these... 73, Steve NU7B ______________________________________________________________ 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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Steve,
There may be a slight change in the pitch of the received signal when changing filters, but it should be limited to 20 Hz or less. If it is more than that, you will have to do a good filter alignment. I recommemd using Spectrogram and a noise generator so you can see what you are doing, but lacking the wideband noise generator, the same thing can be accomplished with band noise. See my website www.w3fpr.com article on K2 Dial Calibration for more information. Part 3 of that article deals with aligning the filters (adjust the BFO frequency to shift the passband), and has links to help setting up and using Spectrogram. Even though the latest version of Spectrogram is now freeware, I recommend you use version 5.17 (download from Tom Hammond's website www.n0ss.net) because the 'how-to' information is written for that version - the screenshots may differ for other versions (but are similar). Yes, the K2 places the VCO on the high frequency side of the signal frequency for bands up through 17 meters, but at 15 meters and above, the VFO is on the low side - that is what causes the sideband inversion. If you prefer to listen to CW in LSB for all the bands, then switch to CW reverse for 15, 12 and 10 meters. Stephen Rector wrote: > I'm new to the list, with a couple of questions on the K2. My s/n 6770 > has been running for about a week: this weekend put in the KSSB2, > KDSP2 and KNB2. When I select from the four CW xtal filter bandwidths, > I get a slightly different pitch on the received CW station. > > Qusetion 1: Is that pitch change directly due to the offset I have > dialed in during the filter calibration? > > The circuit changes the bandwidth of the Cohn crystal filter and, at > the same time, I dial in an offset to center that new passband to my > desired pitch. So, I'm confused why the pitch changes - maybe it's > just calibration error because the tuning step is coarser than my ear. > > Question 2 is an observation: CW mode is LSB all the way to 17 meters, > then USB from 15M up. This is normal, right? On previous > (upconverting) radios it's always been USB from 20M up, so this > surprised me. > > Thanks for any help with these... > > 73, > > Steve NU7B > ______________________________________________________________ > 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 > ------------------------------------------------------------------------ > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 8.5.392 / Virus Database: 270.13.31/2264 - Release Date: 07/26/09 11:07:00 > > 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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Hi Don:
I will check your article out, and thanks again. Last I checked today, the pitch change was slight, so I'll keep an ear on it. And I'll try Spectrogram at some point, after the construction is done. Still have the PA and KAT-100 to go.... It's nice to have the knowledge base that you and others are willing to share. Cheers, Steve On Jul 26, 2009, at 5:16 PM, Don Wilhelm wrote: > Steve, > > There may be a slight change in the pitch of the received signal > when changing filters, but it should be limited to 20 Hz or less. > If it is more than that, you will have to do a good filter > alignment. I recommemd using Spectrogram and a noise generator so > you can see what you are doing, but lacking the wideband noise > generator, the same thing can be accomplished with band noise. See > my website www.w3fpr.com article on K2 Dial Calibration for more > information. Part 3 of that article deals with aligning the filters > (adjust the BFO frequency to shift the passband), and has links to > help setting up and using Spectrogram. Even though the latest > version of Spectrogram is now freeware, I recommend you use version > 5.17 (download from Tom Hammond's website www.n0ss.net) because the > 'how-to' information is written for that version - the screenshots > may differ for other versions (but are similar). > > Yes, the K2 places the VCO on the high frequency side of the signal > frequency for bands up through 17 meters, but at 15 meters and > above, the VFO is on the low side - that is what causes the sideband > inversion. If you prefer to listen to CW in LSB for all the bands, > then switch to CW reverse for 15, 12 and 10 meters. > > Stephen Rector wrote: >> I'm new to the list, with a couple of questions on the K2. My s/n >> 6770 has been running for about a week: this weekend put in the >> KSSB2, KDSP2 and KNB2. When I select from the four CW xtal filter >> bandwidths, I get a slightly different pitch on the received CW >> station. >> >> Qusetion 1: Is that pitch change directly due to the offset I have >> dialed in during the filter calibration? >> >> The circuit changes the bandwidth of the Cohn crystal filter and, >> at the same time, I dial in an offset to center that new passband >> to my desired pitch. So, I'm confused why the pitch changes - >> maybe it's just calibration error because the tuning step is >> coarser than my ear. >> >> Question 2 is an observation: CW mode is LSB all the way to 17 >> meters, then USB from 15M up. This is normal, right? On previous >> (upconverting) radios it's always been USB from 20M up, so this >> surprised me. >> >> Thanks for any help with these... >> >> 73, >> >> Steve NU7B >> ______________________________________________________________ ______________________________________________________________ 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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In reply to this post by NU7B
On Jul 26, 2009, at 7:37 PM, Stephen Rector wrote: > Qusetion 1: Is that pitch change directly due to the offset I have > dialed in during the filter calibration? Mostly. If you pick the right offset, you can get it real close. One tip is to try calibrating one count in either direction to see if it is any better. The BFO DAC does have a minimum resolution -- but you should be able to get the filters to all be within 20 Hz or so of each other. > The circuit changes the bandwidth of the Cohn crystal filter and, at > the same time, I dial in an offset to center that new passband to my > desired pitch. So, I'm confused why the pitch changes - maybe it's > just calibration error because the tuning step is coarser than my ear. Could be, do the best you can. > Question 2 is an observation: CW mode is LSB all the way to 17 meters, > then USB from 15M up. This is normal, right? On previous > (upconverting) radios it's always been USB from 20M up, so this > surprised me. The K2 synthesizer inverts the sidebands above 20 MHz, so the sideband is inverted as well. You're still listening to LSB on CW, but it is using the USB filter settings because of the inversion. The signals also tune backwards from the lower bands. If it bothers you, you can switch to CW reverse, which is USB but tunes like LSB on the lower bands because of the inversion. Bill Coleman, AA4LR, PP-ASEL Mail: [hidden email] Web: http://boringhamradiopart.blogspot.com Quote: "Not within a thousand years will man ever fly!" -- Wilbur Wright, 1901 ______________________________________________________________ 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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