Hello Said,I have seen something similar with my 53132A. I was checking on the delay variation of an amplifier distributing 10 MHz, and noticed a regular sinusoidal pattern, about a third of a nanosecond peak-to-peak, with a period of about 70 seconds. This looked like interference from an off-frequency signal. I hadn't bothered to lock the counter to an external reference, and on measuring a Rubidium source against its internal oscillator, got a reading about 1.4 x 10^-9 high, which matched perfectly this 70-second period Locking the counter to an external reference, this beating went away. Attached is a small GIF that shows the counter readings for twenty minutes before and after applying the locking signal. (Readings were taken once a second, and to smooth the graph slightly, each point on the graph is obtained by averaging ten readings.)
Could this be your problem, Said?
Peter Vince
Said asked:
some time ago we talked about curious humps in the ADEV of the SRS PRS-10 Rb at around 20s intervalls. I think I may have more info on that (and as usually that raises more questions): Below is a capture of the phase offset between a PRS10 1PPS output compared to the Jackson-Labs Fury 1PPS output as measured with a 53132A. The Fury output has been shifted by about 80ns to give a nice phase offset for the 53132A to measure. Besides the underlying counter noise, there clearly is a jump of about 0.5 - 1ns visible exactly once every 15 seconds! Indicated by arrows. Could this be the counter self-calibrating? This is too regular to be co-incident. Has anyone else seen this?
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