New K3EXREF results
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See my test results of the K3EXREF:
http://www.kl7uw.com/K3EXREF.htm When installed and referenced to a good 10-MHz external source the TCXO will be periodically corrected in frequency to keep the K3 on frequency. The display on REF*CAL merely indicates the value the TCXO has been offset to keep the radio on frequency and is not the freq. error. You need to measure the RF frequency with an accurate freq. counter to measure that. I have a counter that is locked to a Rubidium good to +/- 5E-11 and the max error at 50-MHz was +2-Hz (2/50,000,000) The value displayed on REF*CAL will start at 49.380 and they shift over about 30-minutes as the TCXO heats and stabilizes. K3EXREF keeps the radio on freq throughout this warm-up. Without K3EXREF the radio would shift freq with the TCXO (within 1ppm = +/-1E-6). Before the K3EXREF was available you had the option to entering a fixed offset to correct frequency (which should be done after the TCXO has warmed up and stabilizes). The number displayed is a similar offset but now controlled periodically by the external reference source, keeping the K3 more accurate. 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 50-1.1kw?, 144-1.4kw, 432-QRT, 1296-?, 3400-? DUBUS Magazine USA Rep [hidden email] ====================================== ______________________________________________________________ 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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Ed's description provides a good overview but I can add a couple things that might help
fill in some details. There are two TCXO specs of general interest. One is absolute frequency accuracy relative to 49,380,000 Hz, and the other is stability or drift. The absolute accuracy of the TCXO will vary from one K3 to another and really isn't critical since it can be corrected for by setting the REF*CAL value. K3 firmware uses the REF*CAL frequency in calculating the VFO / synthesizer frequency. The K3EXREF uses the external 10MHz frequency reference to accurately measure the actual TCXO frequency, which is then used to automatically update REF*CAL. With a K3EXREF running, and watching REF*CAL change during K3 warmup, you are seeing the drift of the TCXO as its measured frequency gets updated. The TCXO output frequency is never controlled. A benefit of this approach is that there is no degradation to phase noise. 73, Rich AC7MA On 10/30/2011 10:34 AM, Edward R. Cole wrote: > See my test results of the K3EXREF: > http://www.kl7uw.com/K3EXREF.htm > > When installed and referenced to a good 10-MHz external source the > TCXO will be periodically corrected in frequency to keep the K3 on > frequency. The display on REF*CAL merely indicates the value the > TCXO has been offset to keep the radio on frequency and is not the > freq. error. You need to measure the RF frequency with an accurate > freq. counter to measure that. I have a counter that is locked to a > Rubidium good to +/- 5E-11 and the max error at 50-MHz was +2-Hz (2/50,000,000) > > The value displayed on REF*CAL will start at 49.380 and they shift > over about 30-minutes as the TCXO heats and stabilizes. K3EXREF > keeps the radio on freq throughout this warm-up. Without K3EXREF the > radio would shift freq with the TCXO (within 1ppm = +/-1E-6). > > Before the K3EXREF was available you had the option to entering a > fixed offset to correct frequency (which should be done after the > TCXO has warmed up and stabilizes). The number displayed is a > similar offset but now controlled periodically by the external > reference source, keeping the K3 more accurate. > > > 73, Ed - KL7UW, WD2XSH/45 > ====================================== > BP40IQ 500 KHz - 10-GHz www.kl7uw.com > EME: 50-1.1kw?, 144-1.4kw, 432-QRT, 1296-?, 3400-? > DUBUS Magazine USA Rep [hidden email] > ====================================== > > ______________________________________________________________ > 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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Rich,
Thanks for the detailed explanation. I believe Wayne posted this info as well, but it should be in the manual if it isn't. I'll look again, but don't recall any theory of ops for the K3EXREF in its manual. 73, matt W6NIA On Sun, 30 Oct 2011 13:32:18 -0700, you wrote: >Ed's description provides a good overview but I can add a couple things that might help >fill in some details. > >There are two TCXO specs of general interest. One is absolute frequency accuracy relative >to 49,380,000 Hz, and the other is stability or drift. The absolute accuracy of the TCXO >will vary from one K3 to another and really isn't critical since it can be corrected for >by setting the REF*CAL value. K3 firmware uses the REF*CAL frequency in calculating the >VFO / synthesizer frequency. > >The K3EXREF uses the external 10MHz frequency reference to accurately measure the actual >TCXO frequency, which is then used to automatically update REF*CAL. With a K3EXREF >running, and watching REF*CAL change during K3 warmup, you are seeing the drift of the >TCXO as its measured frequency gets updated. The TCXO output frequency is never >controlled. A benefit of this approach is that there is no degradation to phase noise. > >73, >Rich AC7MA > > >On 10/30/2011 10:34 AM, Edward R. Cole wrote: >> See my test results of the K3EXREF: >> http://www.kl7uw.com/K3EXREF.htm >> >> When installed and referenced to a good 10-MHz external source the >> TCXO will be periodically corrected in frequency to keep the K3 on >> frequency. The display on REF*CAL merely indicates the value the >> TCXO has been offset to keep the radio on frequency and is not the >> freq. error. You need to measure the RF frequency with an accurate >> freq. counter to measure that. I have a counter that is locked to a >> Rubidium good to +/- 5E-11 and the max error at 50-MHz was +2-Hz (2/50,000,000) >> >> The value displayed on REF*CAL will start at 49.380 and they shift >> over about 30-minutes as the TCXO heats and stabilizes. K3EXREF >> keeps the radio on freq throughout this warm-up. Without K3EXREF the >> radio would shift freq with the TCXO (within 1ppm = +/-1E-6). >> >> Before the K3EXREF was available you had the option to entering a >> fixed offset to correct frequency (which should be done after the >> TCXO has warmed up and stabilizes). The number displayed is a >> similar offset but now controlled periodically by the external >> reference source, keeping the K3 more accurate. >> >> >> 73, Ed - KL7UW, WD2XSH/45 >> ====================================== >> BP40IQ 500 KHz - 10-GHz www.kl7uw.com >> EME: 50-1.1kw?, 144-1.4kw, 432-QRT, 1296-?, 3400-? >> DUBUS Magazine USA Rep [hidden email] >> ====================================== >> >> ______________________________________________________________ >> 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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