Dave, Just FYI, When I multiply an oscillator to 10GHz, this problem is significantly exacerbated. When I used a crystal oscillator in my rig I could literally blow on the metal box (10GHz rig) while listening to a tone and hear the radio wander off frequency. 5Hz of wander at 10MHz = 5kHz at 10GHz so you hear signals exit the passband of the radio as the temp changes!
>From the research I did, I found that the typical specs on TCXOs tend to be very conservative -- what typically happens is that they are more stable in the center of the temp range (less df/dT) than on the ends of it. Locking your LO to a 10MHz reference locked to GPS, Rubidium, etc. fixes this problem. Steve Stephen Hicks, N5AC, AAR6AM VP Engineering FlexRadio Systems™ 13091 Pond Springs Road, #250 Austin, TX 78729 Phone: 512-535-4713 x205 Email: st...@flex-radio.com Web: www.flex-radio.com *Tune In Excitement™* PowerSDR™ is a trademark of FlexRadio Systems On Mon, Oct 4, 2010 at 06:51, David McClain <d...@refined-audiometrics.com>wrote: > OMG!! I found the cause of the oscillator wander! > > Just to be absolutely sure that I'm comparing apples with apples, I put all > three radio audio outputs into an audio mixer and then fed the resulting mix > into one soundcard, feeding SpectrumLab. The radios were all tuned to 9.985 > MHz to give a 1500 Hz tone on the main carrier of WWV. The Flex was offset > +5 Hz, and the QS1R was offset -5 Hz, with the Icom Pro3 centered. > > I was watching this slow drift unfold over time, and then a curious > "coincidence" happened... The Icom stayed centered while the Flex and the > QS1R nearly simultaneously began a rapid shift (in opposite directions). And > after about 15 minutes, they both reached their maximum deviation in > frequency and then began a slower drift back toward their originally > assigned frequency offsets. Um.... yeah.... > > I watched this occur repeatedly. The QS1R would move a minute or so before > the Flex 3K, and it would move farther in frequency, but both moved > essentially together. What is happening at 45 minute intervals that would > affect both radios at the same time??? > > I live in Tucson. The radios are on a desktop in a far corner of a rather > large living room. Sure enough, whenever the central air conditioning cycled > on, blowing cold air from a distant ceiling vent, that is when the radios > began their rapid sawtooth rise. And when the central air finished its > roughly 5 minute period of blowing, that's when both radios reached their > peak departures and then began a slow drift back to their assigned offsets. > > Dang!!! I guess there is about a 5-10 degree variation. I see about 4 Hz > variation in the Flex3K, and about 5-6 Hz in the QS1R. And that is what is > causing my weird TCXO sawtooths. I see about 4 Hz variation in the Flex3K, > and about 5-6 Hz in the QS1R. The IC756 is so well insulated that it hardly > registers any change down inside the case. The QS1R is very small and has a > lower thermal mass than the Flex3K, and that's why it begins showing about 1 > minutes before the Flex3K. But the QS1R and the Flex3K are absolutely phase > locked to the thermal cycling induced by the central air conditioner. Cold > air was blowing directly across the radios... > > Thought you might want to know. > > - de Dave, N7AIG > > > Dr. David McClain > Chief Technical Officer > Refined Audiometrics Laboratory > 4391 N. Camino Ferreo > Tucson, AZ 85750 > > email: d...@refined-audiometrics.com > phone: 1.520.390.3995 > web: http://refined-audiometrics.com > > > > _______________________________________________ > FlexRadio Systems Mailing List > FlexRadio@flex-radio.biz > http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz > Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ > Knowledge Base: http://kc.flexradio.com/ Homepage: > http://www.flexradio.com/ > _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
