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.