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 +0000, 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.
