Re: [time-nuts] Best phase detector / mixer for 100MHz?
Bill, >> One way to avoid the problem in the 1/f noise region is to avoid it. >> Mix down to a few kHz and analyze you signal This is a good point! Using my SW (www.hpw-works.com) simple set the x-scaling to a center frequency & bandwidth of your choice with enough space in the lower region. This is implemented out of the box. It's like a measurement using the d-jitter but with a costume center frequency. See also the pictures on my homepage with zooming into the 0.005 Hz region using a large sample size. Required is that the source oscillators are stable... Hanspeter >> -Original Message- >> From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On >> Behalf >> Of Bill Fuqua >> Sent: Donnerstag, 29. November 2012 18:02 >> To: time-nuts@febo.com >> Subject: Re: [time-nuts] Best phase detector / mixer for 100MHz? >> >> At 03:56 PM 11/29/2012 +, you wrote: >> > > 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. >> >> One way to avoid the problem in the 1/f noise region is to avoid it. >> Mix down to a few kHz and analyze you signal or if you must mix down to "DC" >> then chop it to bring it up to a kHz or so and analyze it using a program >> such >> as spectrum lab or in software to internally mix back down to "DC" using >> software digital mixer and then analyze. >> You can use a MOSFET analog switch to chop the signal. >>When you chop it you will have an carrier with upper and lower sidebands. >> You can simply take the FFT data and either shift the bins making the carrier >> (chopping frequency) the Zero or DC bin or even better yet add the upper and >> lower sidebands so that you get a 3db improvement in S/N. I will be db since >> the sidebands are identical mirror of each other, ie voltage doubles when >> they >> are added increasing the signal by 6db but noise introduced by electronics on >> upper and lower sidebands are not coherent and only increases by 3db. >> >> 73 >> Bill wa4lav >> >> >> >> >> ___ >> 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.
Re: [time-nuts] Best phase detector / mixer for 100MHz?
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.
Re: [time-nuts] Best phase detector / mixer for 100MHz?
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. Just download the evaluation version with fully feature set. HpW ___ 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.
