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Upgrading Counter 53220A to Option 010 Ultra High-stability OCXO Timebase?
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Andrew:
I'm considering a similar upgrade to a 53220A using the Abracon AOCJY3 10ppb part.

A couple of questions in relation to ocxo's:

1) Abracon offer a 5ppb option in the AOCJY3 series however it's temperature range is restricted to 0 to 50C. The 10ppb part is -20 to 70C. What would be the maximum ambient temperature that the 50C part reliably operate?

2) The lock range to an external reference is narrower for the oem ocxo part, 0.2ppm, versus 2ppm for the tcxo part. Does this mean there is some performance gain using the ocxo even with an external reference? Perhaps this would be noticable on the faster 53230 model?

Thanks
Andrew
jpb:
If you're using the counter indoors I'd think that the 0 to 50C part should be fine (temperature wise - I don't know about its suitability generally), it is very unlikely that the internals of a counter would get significantly hotter than the ambient - they are not high power devices and the main source of heat would probably be the ocxo but it would be in quite a lot of empty space. If you're planning on using the counter in on expeditions to the Sahara or the South Pole it might be better to use the wider temperature range or if you keep the counter in a rack with hot, high power gear on either side.

The narrow lock range is because ocxos generally have a much narrower tuning range (frequency versus voltage gain). They are better quality crystals (SC cut) but for the purposes of a counter there would be no advantage when it is locked to an external source as the external source will determine the timing over longer periods such as that of the counter gate. For RF generators the phase noise is more important but for a counter it is of less importance.

Here is a quote from the Stanford Research Systems SR620 counter manual:

--- Quote ---EXTERNAL TIMEBASES
The SR620 has a rear panel input that will accept either a 5 or 10Mhz external timebase.  The SR620 phase-
locks its internal timebase to this reference.  The phase-locked loop has a bandwidth of about 20Hz and thus
the  characteristics  the  the  SR620's  clock,  for  measurement  times  longer  than  50ms,  become  that  of  the 
external  source.    For  shorter  measurement  times  the  clock  characteristics  are  unimportant  compared  to  the 
internal jitter (25ps rms) of the SR620.  Thus, if the signal from a Cesium clock is input into a SR620 with a 
standard TCXO oscillator the short-term and long-term stability of the SR620 will become that of the Cesium clock. 

--- End quote ---
Andrew:
Thanks jpb that answers many questions.

Interesting that measurement times shorter than the PLL bandwidth are not considered important compared to the internal clock jitter. I would have thought this would be an issue for counters like the SRS620 25ps and Keysight 35ps 53230A but apparently not.
pamphonica:
I just put in a Vectron C4550A1-0213 from Ebay (from China) into my 53220A. It oscillates fine but the internal reference voltage output seems to be missing (looks like open-circuit), so the calibration routine failed.

My fix (for now) was to re-install R828 (0R) which re-connects the internal +5v reference to the adjustment circuitry. This strap was needed for the original smaller oscillator module as it has no reference voltage output.  Cal worked perfectly once this was done.

Has anyone put in one of these specific new/used devices from Ebay and tried the "Cal Step" routine? If this is a feature of this secondhand module, so be it, but if yours worked fine, than please let me know so I can get a replacement from the vendor.

The datasheet shows that ref voltage output can be removed as an option.

-Jeremy
TheSteve:

--- Quote from: pamphonica on December 18, 2019, 08:00:04 pm ---I just put in a Vectron C4550A1-0213 from Ebay (from China) into my 53220A. It oscillates fine but the internal reference voltage output seems to be missing (looks like open-circuit), so the calibration routine failed.

My fix (for now) was to re-install R828 (0R) which re-connects the internal +5v reference to the adjustment circuitry. This strap was needed for the original smaller oscillator module as it has no reference voltage output.  Cal worked perfectly once this was done.

Has anyone put in one of these specific new/used devices from Ebay and tried the "Cal Step" routine? If this is a feature of this secondhand module, so be it, but if yours worked fine, than please let me know so I can get a replacement from the vendor.

The datasheet shows that ref voltage output can be removed as an option.

-Jeremy

--- End quote ---

I've used that exact OCXO - you should not need to install R827 or R828 for it to work perfectly.
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