Hi Would be nice to use something like the ADS1278.
http://www.ti.com/product/ads1278 Lots of channels to cross correlate, and very little flicker noise. Bob On Nov 28, 2012, at 9:29 AM, Support HpW-Works.com <supp...@hpw-works.com> wrote: > Hi Bruce, > >>> The equivalent phase noise (measured in dBc/Hz) is essentially independent >>> of >>> the sample size. > > The dBc/Hz normalization is based on this (also the sample rate). While the > sample > rate & sample size = FFT Bin size (resolution or filter band width) is used > to get > the required correction factor of the spectrum to get the dBc / (1Hz) Y > scaling > back. > >>> So increasing the sample size isnt particularly useful for reducing the >>> phase >>> noise floor. > > By theory, yes... but we use a sound card with a lot of flicker noise on the > lower > end, also we have the 10...20Hz low freq. cutoff due the usage of a servo / > single > 5V power. Also the raising noise below 100Hz (ADC serve & noise on the ADC > power / > input circuit) limits the performance. > > In my simple test increase of the sample size reduced the noise floor in > better way > than just using sample size with 1-2K and large averaging cycles. > > Keep in mind, Bin resolution is sample rate / sample size: > > Example: > > - 32khz / 32678 = about 1Hz > - 32khz / 1024 = about 31 Hz > > >>> However with a sound card plus a mixer a somewhat lower number of samples >>> should suffice since there is no carrier. > > > Ideally the input circuit & ADC of the 3562A would be nice but with much > larger RAM > buffer and ASIO interface O:) > > Hanspeter > >>> -----Original Message----- >>> From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On >>> Behalf >>> Of Bruce Griffiths >>> Sent: Dienstag, 27. November 2012 12:31 >>> To: Discussion of precise time and frequency measurement >>> Subject: Re: [time-nuts] Best phase detector / mixer for 100MHz? >>> >>> Support HpW-Works.com wrote: >>>> Bruce, >>>> >>>> >>>>>> There's no evidence of a cross power spectrum function in this suite. >>>>>> One needs to be able to average at least 10,000 cross power spectra >>>>>> for some applications. >>>>>> >>>> In the PSD (power density)& PSP (power spectrum) there are cross >>>> power and cross power complex average implemented (selectable using the >>> spectrum channel mixer)! >>>> Additional to this you may apply / add averaging of the resulting >>>> spectrum or use additional peak hold. >>>> >>>> Average of 10'000 cross points is a large count and often seen on 1-4k >>> sample size. >>>> Better in my opinion is to use a higher sample size 32k-64k and then >>>> less averaging is required. >>>> >>> The equivalent phase noise (measured in dBc/Hz) is essentially independent >>> of >>> the sample size. >>> So increasing the sample size isnt particularly useful for reducing the >>> phase >>> noise floor. >>> The increased frequency resolution achieved by increasing the sample size is >>> only useful for measuring spurs. >>> In the direct digital method of measuring phase noise a few terasamples (a >>> few >>> gigasamples at baseband) need to be processed to achieve a sufficiently low >>> instrument noise floor. >>> However with a sound card plus a mixer a somewhat lower number of samples >>> should suffice since there is no carrier. >>>> Just download the evaluation version with fully feature set. >>>> >>>> HpW >>>> >>>> >>>> >>> Bruce >>> >>> >>> _______________________________________________ >>> 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.
