Re: [time-nuts] simple explanation of noise spectra with mixing
On 3/1/15 10:23 AM, Joseph Gwinn wrote: time-nuts Digest, Vol 128, Issue 1, Message: 8 Date: Sat, 28 Feb 2015 17:46:18 -0800 From: Jim Lux jim...@earthlink.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: [time-nuts] simple explanation of noise spectra with mixing, etc. Message-ID: 54f26f6a.6030...@earthlink.net Content-Type: text/plain; charset=utf-8; format=flowed Is there a handy one pager kind of explanation of noise spectra after some forms of signal processing.. The best source for the math is probably Fred Walls: F. L. Walls, “Correlation between upper and lower sidebands” IEEE Trans. UFFC, Vol. 47, pp 407-410, 2000. PM and AM Noise of Combined Signal Sources, Fred L. Walls, Total Frequency, fredlwa...@cs.com, Proceedings of the 2003 IEEE International Frequency Control Symposium and PDA Exhibition Jointly with the 17th European Frequency and Time Forum, 0-7803-7688-9/03/$17.00 © 2003 IEEE, pages 532-540. I'll look those up.. I was hoping that someone, somewhere had done a guide to phase noise in 1 or 2 pages or a poster. There's lots of pieces scattered hither and yon, but before I spent much time generating my own.. Kind of like that cool plot that a time-nut has which shows the spectra and allan dev of the various colors of noise in a table. For instance, if you have a oscillator which has a 1/f characteristic, and you mix it with itself, what is the spectra of the output of the mixer. Mixing is a multiplicative process, so this is equivalent to squatting the signal, which doubles its frequency, so the effect will be 20 Log10(2)= 6 db increase of phase noise on the double-frequency terms. I assume you mean squaring.. True, the 2 f term will have 6dB more.. But what about the baseband/DC component.. Your bottom-line question will be if there is any cancellation of phase noise; this will involve the time delay for the rata signal to get to the target and return. My guess is that there will be no cancellation. Short ranges (1 km) so actually, lots of cancellation. the round trip delay is 6 microseconds, so a variation at, say, 10 Hz, is pretty well cancelled out. ___ 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] simple explanation of noise spectra with mixing
time-nuts Digest, Vol 128, Issue 1, Message: 8 Date: Sat, 28 Feb 2015 17:46:18 -0800 From: Jim Lux jim...@earthlink.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: [time-nuts] simple explanation of noise spectra with mixing, etc. Message-ID: 54f26f6a.6030...@earthlink.net Content-Type: text/plain; charset=utf-8; format=flowed Is there a handy one pager kind of explanation of noise spectra after some forms of signal processing.. The best source for the math is probably Fred Walls: F. L. Walls, “Correlation between upper and lower sidebands” IEEE Trans. UFFC, Vol. 47, pp 407-410, 2000. PM and AM Noise of Combined Signal Sources, Fred L. Walls, Total Frequency, fredlwa...@cs.com, Proceedings of the 2003 IEEE International Frequency Control Symposium and PDA Exhibition Jointly with the 17th European Frequency and Time Forum, 0-7803-7688-9/03/$17.00 © 2003 IEEE, pages 532-540. For instance, if you have a oscillator which has a 1/f characteristic, and you mix it with itself, what is the spectra of the output of the mixer. Mixing is a multiplicative process, so this is equivalent to squatting the signal, which doubles its frequency, so the effect will be 20 Log10(2)= 6 db increase of phase noise on the double-frequency terms. Your bottom-line question will be if there is any cancellation of phase noise; this will involve the time delay for the rata signal to get to the target and return. My guess is that there will be no cancellation. Or if you have a 1/f^3 characteristic (e.g. from a crystal oscillator, very close in) or a 1/f^2 (from a VCO). The double rule will apply to each point in the phase noise as if it were alone. Specifically, I've got some folks working with homodyne radars (where you demodulate the received signal with a sample of the transmitted signal, but sometimes with an offset mixed in, etc.) and I'm looking for a quick intro to this kind of thing at a sort of empirical/phenomenological as opposed to analytical.. If you see X on a spectrum analyzer or FFT, it is because of Y... Similarly, they're building PLLs and know about the 20log10(N) thing, but what should the shape of things underneath be. The 20Loh10(N) applies regardless of offset frequency, so the whole phase noise spectrum will move up and down as a unit. Joe Gwinn ___ 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] simple explanation of noise spectra with mixing, etc.
Is there a handy one pager kind of explanation of noise spectra after some forms of signal processing.. For instance, if you have a oscillator which has a 1/f characteristic, and you mix it with itself, what is the spectra of the output of the mixer. Or if you have a 1/f^3 characteristic (e.g. from a crystal oscillator, very close in) or a 1/f^2 (from a VCO). Specifically, I've got some folks working with homodyne radars (where you demodulate the received signal with a sample of the transmitted signal, but sometimes with an offset mixed in, etc.) and I'm looking for a quick intro to this kind of thing at a sort of empirical/phenomenological as opposed to analytical.. If you see X on a spectrum analyzer or FFT, it is because of Y... Similarly, they're building PLLs and know about the 20log10(N) thing, but what should the shape of things underneath be. ___ 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.
