Hi, Thanks this is good advice.
Pointing the spectrum analyzer to fc + delta seems to be similar than deducing phase noise from the ZCD output since this would be with reference to (fc + delta) in any how? Provided the aliasing issue can be sorted. Regarding the aliasing issue - in order to plot phase noise up to 100kHz I would use a 300kHz beat sampled at 100MHz (which is the sampling system I got available). Obviously, making sure I have sufficient bandwidth in all areas. Cheers. Stephan. On 10 March 2011 10:50, Bruce Griffiths <bruce.griffi...@xtra.co.nz> wrote: > For conventional phase noise measurements at offsets in the (10Hz, 20kHz) > range one can use a sound card with a low noise preaamp. > Suitable sound card preamps with lower noise floors than Enrico's or > Wenzel's designs can be built using readily available components. > Wider bandwidths ( up to 1MHz or so) are not difficult to achieve. > > Bruce > > > Stephan Sandenbergh wrote: > >> Hi, >> >> Cross-correlation a very clever idea! Thanks for the reference - Rubiola >> got >> some good sources of reference on his home page. >> >> One thing though - for a phase-noise kit one will probably need to replace >> the ZCD with a low-noise amplification stage of around 80dB to be to allow >> sampling at ADC voltage levels? >> >> Cheers, >> >> Stephan. >> >> On 8 March 2011 22:28, Magnus Danielson<mag...@rubidium.dyndns.org> >> wrote: >> >> >> >>> On 03/08/2011 07:46 PM, Stephan Sandenbergh wrote: >>> >>> >>> >>>> Hi, >>>> >>>> I recently noticed something interesting: The DMTD measurement gives a >>>> set >>>> of phase values x(t). From which fractional frequency y(t) is >>>> calculable. >>>> So >>>> now it seems viable to plot the spectrum, Sy(f) and if you scale it >>>> properly >>>> you arrive at Sphi(f). If I'm not making a gross error somewhere the >>>> math >>>> seems to check out. But, I'm wondering is there a physical reason why >>>> this >>>> isn't valid? >>>> >>>> I have not seen this being done anywhere - so I assume there is. >>>> However, >>>> it >>>> seems possible to plot Sphi(f) for 1Hz< f<100kHz when having a vbeat = >>>> 100kHz sampled for 1 second. >>>> >>>> I'm familiar with the loose and tight phase-locked methods of measuring >>>> phase noise, but am quite curious to know if phase noise from a DMTD >>>> measurement is a valid assumption. >>>> >>>> I would guess that if the frequency domain phase noise measurement >>>> requires >>>> phase-lock then the time-domain measurement requires as well. However, >>>> here >>>> in lies my real interest - two GPSDOs are phase-locked (not to 1Hz, >>>> something far less I know) so can it be possible to measure GPSDO Adev >>>> and >>>> phase-noise using a single DMTD run? Am I making a wrong assumption >>>> somewhere? >>>> >>>> >>>> >>> An architecture not completely different to the DMTD architecture is used >>> in phase-noise kits. Instead of having two sources and one intermediary >>> oscillator is instead there one source and two intermediary oscillators. >>> The >>> oscillators is locked to the carrier frequency rather than an offset. The >>> mixed down signal is then cross-correlated to get the spectrum. >>> Increasing >>> the averaging factor and the spectrum can be suppressed below that of the >>> intermediary oscillators. Since the two intermediary oscillators have >>> uncorrelated noise, the external noise is what correlates over time. This >>> technique is simply called cross-correlation. Such a cross-correlation >>> setup >>> can run very close to the carrier in terms of offsets. >>> >>> In contrast will a DMTD with it's offset frequency be problematic at low >>> offsets since the positive and negative offsets noise will not occur at >>> the >>> same frequency in a DMTD setup. Consider a a DMTD with a 10 Hz offset, >>> pointing a spectrum analyzer on 100 Hz will measure the down-converted >>> average of carrier+(100-10) Hz and carrier-(100+10) Hz, thus carrier+90 >>> Hz >>> and carrier-110 Hz. >>> >>> Creating a mixed-mode setup for phase-noise/DMTD will however be >>> possible. >>> >>> So, DMTD as such is relatively limited, but add an RF switch and another >>> oscillator and you get a cross-correlation phase-noise kit. >>> >>> To turbo-charge the phase-noise kit use a quadrature combiner and >>> amplitude >>> adjustment to create a interferometric mixdown, working around part of >>> the >>> mixer limitations. Enrico Rubiola has writen about this approach. >>> >>> Cheers, >>> Magnus >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >>> >>> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> >> > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.