In article <[EMAIL PROTECTED]>, "David L. Mills" <[EMAIL PROTECTED]> wrote:
> Joseph, > > I took a look at the instrument instruction manual to see what is going > on. In typical todayspeak, Symmetricom doesn't say how the gadget works. > I make it what used to be called a Costas direct-conversion receiver. > The test signal is connected to two mixers; the reference oscillator is > connected to the other mixer inputs in quadrature. The mixer outputs are > digitized and filtered, the Q signal is shifted 90 degrees from the I > signal and combinted. The result is a baseband SSB dignal which is then > Fourier transformed for display. Is this what you have in mind? Yes, but not quite the whole story. Although impossible to discern from Symmetricom's 5120 datasheet and users guide, there is more to it than that. I found this instrument by accident while researching the literature for DMTD information. This search led me to Timing Solutions Corp (which was bought by Symmetricom in 2006) and "Direct-Digital Phase-Noise Measurement", J. Grove, J. Hein, J. Retta, P. Schweiger, W. Solbrig, and S.R. Stein, 2004 IEEE International Ultrasonics, Ferroelectrics, and Frequency Control Joint 50th Anniversary Conference, pages 287-291. But if this is an advance in the technology, there could be a patent, and there was: "Two-Channel Digital Phase Detector", US Patent 7,227,346 to Wayne E. Solbrig. I then approached Symmetricom, which led me to the 5120 (1 MHz to 30 MHz) and the 5125 (future, 1 MHz to 400 MHz). A section of the above article appears in the 5120 users guide. I have no idea why Symmetricom doesn't really mention that the 5120 can do these things, but I assume that the market for phase noise test sets vastly exceeds all other markets for a 5120-like instrument. I borrowed an early demo 5120 instrument, and in my somewhat slapdash lab setup, it was easily able to resolve 0.01 picosecond (eyeball rms width of the traces) changes in delay at 10 MHz while using a very quiet oscillator (a Symmetricom 1050A), after warming up overnight. Joe Gwinn > Dave > > Joseph Gwinn wrote: > > > In article <[EMAIL PROTECTED]>, > > Joseph Gwinn <[EMAIL PROTECTED]> wrote: > > > > > >>I may need a Dual Mixer Time Difference (DMTD) instrument, to measure > >>picosecond changes in electrical length in a coax plus amplifier time > >>reference signal distribution system with total delays in the hundreds > >>of nanoseconds, currently operating at 10 MHz (sinewave), but with 100 > >>MHz likely at some future date. > >> > >>What DMTD instruments are commercially available? A google search was > >>not successful - all noise no detectable signal, probably because DMTD > >>instruments are not that common, and many people build their own. > > > > > > The silence, the silence. I have not found too many commercial DMTF > > units, but I have found one, although the maker does not market it a > > such: > > > > The Symmetricom 5120 > > <http://www.symmttm.com/products_pn_adev_test_sets_5120A.asp> is at > > heart a digital DMTD instrument, and will make all the usual DMTD > > measurements, although it is marketed primarily as a phase noise test > > set. > > > > What else is available? > > > > > > Joe Gwinn _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
