At 09:26 PM 8/9/2007, Tom Clark, K3IO wrote: >Jim Lux wrote: >> >> >> >>I assume you've got the 8640s locked to a common source (or each other). >> >> >Highly unlikely -- the 8640s are free-running >oscillators with excellent short-term phase >noise. Signal is derived from a cavity >oscillator. The have a rudimentary frequency >stabilizer which can lock the last digit of the >frequency from an internal counter, but the >frequency can wander ±½ digit. Hence, the >two-tone measurement is not made with coherent oscillators.
I was kind of wondering about that. I knew they could "lock" after a fashion, but I didn't know how they did it or what the performance was. And, as I think about it, I'm not sure that it would make much difference in a two tone measurement, assuming you're doing some sort of long term power spectrum measurement to see the spurs. Of course, if one claims the biggest spur is 60-70 dB down, that's a non-trivial measurement to make. (depending on what the power spectral density of the noise you're measuring the spur above is.. if the tone is at -10 dBm, and the spur is at -70dBc (-80dBm), your sources have to be substantially quieter, and the measurement bandwidth narrow enough to see the spur above the noise floor...) I'll have to think about it in the HF case. I've been looking at many GHz, and things are sort of different up there. _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio Homepage: http://www.flex-radio.com/
