Esa Wenzel has a introduction to low cost phase noise measurement at:
http://www.wenzel.com/documents/measuringphasenoise.htm Its relatively easy to assemble such a system. A PC sound card can be used as a spectrum analyser for measuring phase noise to within a few Hz of the carrier. There are low noise amplifiers with lower flicker noise than Wenzel's low noise FET input audio amplifier <http://www.wenzel.com/pdffiles1/pdfs/lowamp.pdf>. It is also possible to build a variant of Wenzel's amplifier that doesnt require selection of JFETs. If one wishes to measure the Allan variance of an oscillator, the 3 cornered hat technique can be used with 3 oscillators having similar performance. For longer tau (1000sec or more depending on the OCXO being characterised) the PPS output of a good gps timing receiver can be used as a reference. However a clear view of the southern sky is required, Bruce Esa Heikkinen wrote: > Hello again... > > >> Right, it all depends on what stability you're after. The OCXO >> will have much better short-term stability than the LPRO -- the >> LPRO is close to ten times worse. So do not replace the TBolt >> OCXO with a LPRO if short-term stability is your goal. See: >> > > I'm wondering what could be the cause of this. According to operating > manual LPRO's output should be crystal oscillator (VCXO) generated > signal, which is synchronized to rubidium. So why it is so much worse > than any other crystal oscillator (or other Rd oscillators). Are there > any schematics for LPRO available anywhere? > > I cannot see the any phase noise difference between Trimble's OCXO and > LPRO with spectrum analyser. Measured with different spans from 500 kHz > to 200 Hz, using resolution bandwiths 300 Hz to 6 Hz. So the noise which > is causing bad short term drift must be very close to fundamental. > > It seems that only way to see this noise is to use phase detector > circuit but my problem with that is that I haven't got any good > reference for it and this kind of equipments are quite hard to find here > in Finland. It would be nice to see what kind of noise there are, to > design the filter bandwith for external OCXO lock circuit. > > Other idea to bring that noise visible could be multiplying it with some > kind of comb generator circuit (might be hard to build one). Then it > would be possible to measure it's harmonics. Not sure if there's enough > level present anymore at GHz frequencies... > > What kind of test setup did you use when getting this result: > > LPRO plots: > > http://www.leapsecond.com/museum/lpro/ > > _______________________________________________ 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.
