[time-nuts] PRS-10 findings

[Peter Vince]

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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