John, If the math works out, then I guess it must work.. If one has the time to wait..
Bye, Said Sent From iPhone On Dec 30, 2012, at 16:23, "John Miles" <[email protected]> wrote: >> Bruce, >> >> The Tsc5125A and miles Timepod show a phase noise floor 3dB above the >> noise floor of the two oscillators (if two are used with identical noise > floors). > > Bruce is actually talking about a semi-undocumented trick with the TimePod > that allows it to act like an E5052 or TSC 5120A-01 with two internal > references. Basically, you remove the SMA jumpers from the TimePod's input > jack panel and feed two independent reference sources that are very close to > the same frequency to the Ch0 IN and Ch2 IN jacks. Then you connect your > DUT to the REF IN jack, and flip the channel equations from "0-1" and "2-3" > to "1-0" and "3-2" to reverse the roles of the input and reference sources. > > That allows the cross-correlation algorithm that normally removes the ADC > noise from a PN measurement to remove the uncorrelated noise from your two > references as well. It's a nifty technique, but it is important that the > two references be close to the same frequency for various reasons, some of > which I haven't adequately investigated. So it falls into the "Unsupported > technique/Use at your own risk" category. > >> It would be nice if that worked, then we all could use $10 TCXOs instead > of >> $1000 Wenzel references. > > That's basically how the E5052A/B and TSC 5120A-01 work -- if you look at > their phase noise floor specs, they are much better than what can be > obtained from any one reference source. The E5052A/B instruments actually > use the technique to remove the noise from two VHF-microwave downconverters. > That was my original intent in adding those SMA jacks -- see > http://www.miles.io/timepod/VHF_test_jig.jpg and > http://www.miles.io/timepod/VHF_example_400_MHz.png , where a pair of HP > 8662A synthesizers is used to downconvert a much quieter 400 MHz source for > measurement at 9 MHz. > > In principle you can indeed use a pair of $10 TCXOs as references to measure > arbitrarily low-noise DUTs, but you may need to run the measurement for days > or weeks. Measurement time is the price of the free lunch in this case. > > -- john > Miles Design LLC > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
