I've constructed a homebrew setup to measure time intervals using a software defined radio. Basically a single-channel downconversion to about one hertz, then count samples from the SDR clock to time stamp the zero crossings. This is done in gnuradio and saved to a file for post processing. The resolution is theoretically good, but the accuracy is unknown.
The result produces ADEV vs. Tau charts with reasonably sane looking results. The 'unknown' is a Rubidium oscillator locked to CDMA pilot (TS2700), and the internal crystal oscillator in the SDR radio as the reference. Thus, ADEV probably is mostly measuring that internal crystal rather than the TS2700. Later on a GPSDO will be tried as the reference clock to see if the Adev results are better. It brings up a question: Is it possible to estimate the phase noise of that internal crystal from the ADEV measurements? There are a bunch of papers that go the other way: from Phase Noise to Adev. Searching brings up only one paper that goes from ADEV to Phase Noise but it's text does not seem to be readily available. It apparently models the oscillator as a couple of well known error models. -- Tom, N5EG _______________________________________________ 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.
