[time-nuts] 53132 Option 012 Aging

[Bob Camp]

Hi

The biggest issue I have seen with internal OCXO’s on counters is the actual use
case:

Case A

I have the counter mounted in a rack / on a bench and it’s always on power. 

Case B

I have the counter on the shelf and pull it down and plug it in when I need to use it, once I’m done
I unplug it and put it back on the shelf.

Case C

other.

From what I’ve seen,  roughly 99% of the use falls into either case A or case B. 

In case A above, adding a GPSDO is not a big deal. It benefits all the gear in the rack, not just the counter. It may 
(or may not) pull less power than the counter on idle. If the GPSDO fries from long use, it’s  less 
expensive to replace than a fancy counter. 

Case B is where the problem is.  In case B above, the normal “warm it up for 5 or 10 minutes” 
approach likely leads to an error on the order of 1x10^-8 or more. It’s better than a TCXO, but 
not by as much as it should be.It’s also enough to significantly degrade the accuracy of the counter. 
Worse, the drift over the next hour or so will drive you a bit nuts if you *need* accuracy in what you are doing. 

To get good stability out of an OCXO and not have it on power all the time, you need to be in case C. More or less:

1) Decide I will use the counter tomorrow.
2) Pull it down off the shelf and let it warm up overnight.
3) Do my testing and unplug it when done. 

Yes indeed somewhere there is somebody that organized. If so, I have yet to meet them :)

Is that the whole story - of course not. It *is* worth considering when looking at an internal 
OCXO conversion that likely shortens the lifespan of the counter (more heat / power supply load / 
fan time …). 

Some alternatives:

1) Cheap rubidium in a box - no “couple of days” warmup / retrace stuff to deal with
2) OCXO + batteries in a box - just the OCXO runs, the counter is turned off
3) Lightweight GPSDO - locks up about as fast as the Rb, can be quite accurate.

None of the alternatives are massively expensive. Options 2 and 3 can be quite a bit
smaller than the counter. Option 1 might be about the size of a 53131. 

Bob





> On Apr 12, 2015, at 12:39 PM, John Allen <john at pcsupportsolutions.com> wrote:
> 
> Hi nuts - I ran into this information on the Keysight site.
> 
> The aging rate of a Keysight Option 012 ultra-high-stability oven in the
> first 90 days is:
> 
> 1E-10 *30 days + 3E-9 * 2 months = 9E-9
> 
> In the first year, the aging rate is:
> 
> 1E-10 *30 days + 3E-9 * 11 months = 3.6E-8
> 
> The second year (without adjustments) the aging rate is:
> 
> 1E-10 *30 days + 3E-9 * 11 months + 2E-8*1 year = 5.6E-8
> 
> Above is from:
> Tips for making more accurate measurements with a frequency counter
> http://www.keysight.com/main/editorial.jspx?cc=US
> <http://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey=505277&nid=-3
> 3788.536880944.00&id=505277>
> &lc=eng&ckey=505277&nid=-33788.536880944.00&id=505277
> 
> It makes a case for using a GPSDO or other external reference or frequent
> re-calibrations of the -012 oscillator.
> 
> Regards, John
> 
> 
> 
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