[time-nuts] Counter Internal Oscillator Importance with ExternalReference?

Mattia Rizzi mattia.rizzi at gmail.com
Wed May 10 10:47:03 EDT 2017


>Like most counters, the 53230A has an ext-ref input. But it is horrible.
And the ref output is even worse.

I had similar issues using the ext ref. output of the Agilent 53230A
connected to the Ext. ref input of the 33220A. The frequency synthtized by
the 33220A had pretty bad ADEV values (measured by the 53220A).
I solved it by connecting the chassis of both instruments using the rear
earth cable screw of the two instrumens. The ADEV measured was limited by
the counter resolution (see attachment)
If I have time I'll try to do the opposite, use the free-running 33220A as
reference for the ext ref. input of the 53220A. Indeed, some noise inside
53220a may be cancel out due to the setup, but I don't have another good
counter right now :(


2017-05-09 17:03 GMT+02:00 Tom Van Baak <tvb at leapsecond.com>:

> Hi Thomas,
> About the 53230A -- like many of us I figured there was no point in buying
> the expensive OCXO versions since I have plenty of good 10 MHz references
> around here. So years ago Keysight loaned me two of them for a month: one
> with, and one without OCXO. Like most counters, the 53230A has an ext-ref
> input. But it is horrible. And the ref output is even worse. I think we've
> discussed this on the list before, including ADEV and PN plots. I decided
> not to buy one, ever, until they fixed the problem.
> So it could be a nice counter. Someone at Agilent / Keysight needs to
> re-design the int/ext/mux/pll clock handling of the 53230A; someone who
> understands phase noise and short-term stability; someone who honors the
> intent of ext-ref-in and ref-out; someone who keeps stupid microprocessor /
> LCD / comms / power supply noise out of the clock path. Meanwhile I keep my
> old 53132A's and older SR620's and stay away from the 53230A.
> If you have your own measurements, please share. Maybe I just got a bad
> sample, I don't know. But the ext-ref performance smelled like poor
> engineering to me. My hope is that someone on the list will hack a 53230A,
> fix the problem, and share the solution with us, or even with Keysight.
> /tvb
> > Hi All;
> >
> > How important is the standard, medium, or high stability reference in
> counters like the 53230A, or FCA3120 when locked to an ultra low phase
> noise external reference? Particularly when making measurements and
> adjustments on other ultra high performance references?
> >
> > I know Agilent sold 53132A counters with an option (H01 I believe) that
> bypassed the internal reference completely when and external reference is
> applied, but I think standard configuration on most counter is to
> discipline the internal reference.
> >
> > Thanks for your thoughts.
> >
> > Thomas Knox
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