Steve Rooke wrote: > 2009/8/17 Bruce Griffiths <[email protected]>: > >> [email protected] wrote: >> >>> Please, how do time-nuts measure phase noise? What may be a minimal setup >>> whit recording capability? >>> Thanks, >>> Antonio I8IOV >>> >>> >>> >>> >> A minimal setup for the classical method requires 2 frequency sources at >> the same frequency one of which can be phase locked in quadrature (with >> low loop bandwidth) with the other. >> The output spectrum of the phase detector outside the PLL loop bandwidth >> is then proportional to the relative phase noise spectrum of the 2 >> sources and is measured using a spectrum analyser. >> A double balanced diode mixer is used as a phase detector (most other >> types of phase detectors are far too noisy). >> A sound card with a suitable low noise preamp can be used as an FFT >> based spectrum analyser in the ~10Hz to ~20kHz range, the actual >> frequency limits depend on the sound card and its sampling rate. >> > > So how do you discriminate against the phase noise of the source you > are using as a standard frequency? Do you have to use a known low > phase noise standard to mix with your unknown source? > > Steve > > >> Bruce >> >> 1) Use 3 sources, S1, S2 and X.
2) Phase lock S1 in quadrature to X using a diode double balanced mixer using a low bandwidth PLL. 3) Phase lock S2 in quadrature to X using a diode double balanced mixer using a low bandwidth PLL. Then for frequencies outside the PLL bandwidth the crosspower spectrum of the 2 mixer outputs should be predominantly due to the phase noise X. In practice its best if the phase noise of the 2 standards S1, S2 isn't significantly worse than that of X. It is also desirable that both S1 and X and S2 and X be locked at their respective mixers quadrature point (not necessarily the same as that for zero dc output) Bruce _______________________________________________ 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.
