[time-nuts] Differences / Jitter Between Frequency Standard Sources

David Bobbett d.bobbett at tiscali.co.uk
Thu Nov 24 14:04:30 EST 2011


Just as an aside, you /can /get rid of the 'dithering digit' problem if 
you use a counter which employs a reciprocal counting technique.

I use a Thandar Thirlby TF830 locked to a 10MHz reference derived from a 
Tbolt, but I'm sure there must be others.


David Bobbett, G4IRQ



On 24/11/2011 18:01, Robin Kimberley wrote:
> Any frequency counter will have an given accuracy  +/- the LSD (least
> significant digit), so alternating between  10.0000000 and 9.9999999 looks
> perfectly normal to me.
>
> Rob Kimberley
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Frederick Bray
> Sent: 24 November 2011 17:56
> To: time-nuts at febo.com
> Subject: [time-nuts] Differences / Jitter Between Frequency Standard Sources
>
> I have what would probably be considered to be a "newbie" question, so
> please excuse my likely ignorance.
>
> I have a HP 5385A frequency counter, which I am using with an external
> standard.  If I try to compare one 10 MHz standard against another, using
> one as the external standard and the other as the device being measured, the
> readout fluctuates between 10.0000000 and 9.9999999.  This happens when I am
> comparing a Z3801A and the Trimble look-a-like using the same GPS antenna
> and identical cables (including length) between the GPS antenna splitter and
> the two units.  I have also used identical
> cables between the 10 MHz outputs and the counters.   Hence, cable
> variations shouldn't be the issue.
>
> The same thing happens comparing the Timesource 2700 against either of the
> GPS standards.
>
> Is this attributable to the different standards or the frequency counter?  I
> haven't yet set up a dual trace scope to compare the various sources
> directly, but that will be my next step.
>
> Thanks for any comments, etc.
>
> Fred Bray
> W6WAW
>
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