[time-nuts] Commercial software defined radio for clock metrology

Kevin Rosenberg kevin at rosenberg.net
Fri Jul 29 18:58:03 EDT 2016


Thanks for your very useful paper Oscillator Metrology with SDRs[1]. I
created a C++ program and checked residuals using a 10 MHz clock split
to the A and B channels of a LFRX and BasicRX boards and sampled at 1
Mhz. Using boxcar averaging of 1000 samples at 1 kHz, I was impressed
by the low noise floor approaching that of my Timepod which was
several times the cost. I included the Allan Deviation without
averaging showing the sqrt(1000) increase in noise floor without the

I had a question about your experience. You mentioned using a input
signal near the maximum of the USRP’s ADC to get the best SNR. I
reviewed the schematics and application notes. I found a maximum Vpp
mentioned of 3.3V. I was wondering what voltage you were using to
drive the USRPs. When I go above 1.5-2 Vpp, I start getting signal
distortions and not much increase in the amplitude.

Many thanks for publishing your work in this area.



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