[time-nuts] Z3815A show 0ns Predicted uncertainty

Mark C. Stephens marks at non-stop.com.au
Fri Jun 28 23:51:15 EDT 2013


Charles, rather silly typo on my behalf, without doing the proper research, of course I meant the Symetricom version.

These 5 Z3805A have been running just over 6 weeks. I must have been extremely lucky to strike a batch of good 10811's then.
The Z3815A has gone back up to 100ns PHU now <shrug> 

I wonder is there any way to change the PLL loop adjust using pForth.
There is a command there but I am not sure of the value or range.

-marki

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Charles P. Steinmetz
Sent: Saturday, 29 June 2013 12:46 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Z3815A show 0ns Predicted uncertainty

marki wrote:

>My Z3805A are usually in the 1-4us range.
>I was pleasantly surprised to see the nanoseconds!
>
>I must ask, do you have the later Z3805A with the MTI oscillator?
>Alll mine have the older 10811 Double oven.

Ummmmm...I misplaced some decimals, sorry.  My Z3805A switches to
*nS* when it gets below 1 *uS*, as your Z3815A is apparently trying to do.  24-hour predictions from a GPSDO in the pS range (or even the
<100 nS range) would be meaningless.  My 3805 has a Symmetricom 5 MHz oscillator with doubler, and generally shows a predicted uncertainty from 200 nS to 1 uS after running uninterrupted for a year.  (Note that the increase in predicted stability over time is much more likely to be related to the oscillator settling in than to the 3805's prediction algorithm having more data -- I doubt seriously that the
3805 has a memory longer than days.)

I have not seen a 3805A with an MTI oscillator, but the few 260-series SC-cut OCXOs I've measured have not been particularly good performers compared to a typical 10811.  Of course, unit-to-unit variability may be as large as or even larger than type-to-type differences, so one would need a much larger sample size to draw any useful general conclusions.

Best regards,

Charles




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