Dr. Kirkby, Mike S's query solidified my resolve to get to the bottom of this.
Searching for "phase noise" at your web site brings up a paper that concerns the use of lock-in amplifiers to extract 1 microvolt signals from 3 volts of noise. The setup is described as a modulated laser and a light receiver. Apparently, the laser is modulated with the same sine wave as the lock-in (phase detector) amplifier. [The same technique is used by the ancient Fluke 207 VLF receiver to pull WWVB out of today's man-made noise. The 207 also compensates for offset.] It seems that the sensitivity of the receiver would be affected by the phase noise level of the oscillator. I don't know that. [There was a time when I thought I was educated. Time has changed that.] If the oscillator that modulates the transmitter is not the same as the oscillator for the receiver, then relative phase noise would be all that mattered. At some point there would not be enough phase coherence to obtain lock, no? Is that your reason for raising the noise level of this group? When the full extent of a question is not revealed, it sets off a wave of noisy speculation that is not far from shared ignorance, in some cases. Not that I haven't learned anything from all this, you understand. Kind regards, Bill Hawkins -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Mike S Sent: Wednesday, April 27, 2005 10:28 AM To: Tom Van Baak; Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Upper limit on phase noise from two oscillators. At 10:05 AM 4/27/2005, Tom Van Baak wrote... >Now is low phase noise really what you're after, or >are you more interested in low short- and long-term >Allan Deviation? As a rookie to this, please correct me if my understanding is off. Phase noise is only really relevant to sine wave signals. If one had a perfect square wave source, it would have zero Allan deviation, but significant phase noise, due to it's difference from a pure sine wave. If one is using the repetitive nature of a signal by triggering at a fixed level and slope, phase noise may not have a significant impact on the application, since a figure for phase noise doesn't necessarily imply that the wave shape varies across cycles, nor does it indicate poor Allan deviation. Worse Allan deviation would always be reflected in worse phase noise (because it implies a less than perfect sine wave), but not the other way around. _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
