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

Tom Knox actast at hotmail.com
Tue May 9 21:40:41 EDT 2017

Hi All;

Thanks for the input. Tom a question, was there any difference between the two 53230A oscillator when locked to an external reference? I have also experienced poor results with my 53230A often showing constant reference errors. Sadly I have several each  53230A's Ultra Stab and MCA3027's Med Stab so I cannot directly compare oscillator performance. I am trying to reverse engineer the Tektronix FCA/MCA counter to determine if there is away to directly feed an external reference is a direct reference instead of phase locking the internal reference while keeping the rest of the functionality intact, Which appears possible on these boxes. It appears U11B send off/on signals from pin 3,4,5 to switch between Std3, Oven5, or Rubidium4 internal ref which then provides 10MHz signals to U11B pin 204 RB ,205 Std,206 Oven respectively, What sense and controls that I have yet to determine, the selection may be in the menu. That may allow simple adding a connector and cable to the rear panel. U9A seems to relate PLL and switching. Perhaps the same is possible with the 53230A. I spoke with a friend Fred Walls today and asked if he though the internal reference was much of a factor when Lock to a good external reference and he did not thin so.

Thanks again for everyone's input.

Thomas Knox

From: time-nuts <time-nuts-bounces at febo.com> on behalf of Tom Van Baak <tvb at LeapSecond.com>
Sent: Tuesday, May 9, 2017 9:03 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Counter Internal Oscillator Importance with ExternalReference?

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.


> 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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