[time-nuts] Re: Ref out on Keysight 53230A

[Bob Camp]

Hi

The jump period does not seem to be related to the frequency offset of
the internal oscillator. If the counter is idle, the system locks up and runs
fine. The Ref Out is pretty clean (= they never are 100% clean on any
Ref Out). 

When the problem happens, it is not subtle at all. It will mess up just about
any downstream device to some degree. If you dig into the pops / crud, they
look worse and worse as you zoom in the time scale. Something pretty 
significant *is* going on. 

The jumps appear to be related to the counter finishing a measurement
or group of measurements. They appear to happen when the counter is
(more or less) idling. As far as the internals of the counter are concerned,
the jumps have no impact. 

The counter is very accurate and the jumps are quite big. This tends to 
confirm that they must happen between measurements / readings. If
they happened during a reading, it seems unlikely that the accuracy 
would not be impacted. 

Bob

> On Jan 25, 2023, at 1:44 AM, Erik Kaashoek via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Jürgen
> 
> Is the period of the phase jumps of the ref out related to the frequency difference of the free running internal ref and the external supplied ref?
> If so, this could imply the internal ref couples into the pll locking to the external ref and creates a periodically pull that causes the internal pll to jump.
> If this is the case then the measurements done with the 53230A should also have such a phase jump when an external reference is supplied. Not sure if such a small phase jump would be visible on the 53230A.
> On one of my counters the jump is only visible when I use a rather short (10 ms or lower) gate time but then it is very visible. With a gate time of 1 second the jump is totally invisible
> If the measurements do not have such a  phase jump there is no harm done.
> Erik.
> 
> On 24-1-2023 18:37, Bob Camp via time-nuts wrote:
>> Hi
>> 
>> Yup, that’s the sort of thing it does to the Ref Out.
>> 
>> As long as you don’t use the Ref Out, it’s a very nice counter.
>> 
>> Bob
>> 
>>> On Jan 24, 2023, at 8:32 AM, Jürgen Appel via time-nuts <time-nuts at lists.febo.com> wrote:
>>> 
>>> On Friday, 20 January 2023 01:54:25 CET Bob Camp via time-nuts wrote:
>>> 
>>>> If you put the input and output into a Phase Station, you can see glitches
>>> Never used the external output for something important before, but as the
>>> devices were standing on the table, I wanted a record for the future:
>>> 
>>> Setup: 10 MHz Reference to both "Ext Ref In" and Phase station, "Int Ref Out"
>>> to DUT input of Phase station: Phase drifts rather slowly. As soon as I
>>> connect some ~100MHz input to the 53230A, the "Int Ref Out" shows periodic
>>> phase jumps. Turning the knob to increase the Gating time 0.1s->1s temporarily
>>> disturbs the phase even more; the Glitch period seems unchanged though.
>>> 
>>> Still like this counter though...
>>> 
>>> Cheers,
>>> 	Jürgen
>>> 
>>> 
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