[time-nuts] another Ebay mixup, 5370

Ulrich Bangert df6jb at ulrich-bangert.de
Sun Jun 10 09:32:43 UTC 2007


Gents,

the overall performance of time interval counters not only relates to
their interpolators and nominal resolution but also to a not so well
known extent to the conditoning of the input voltages and the type of
input signal. The following table might give you an idea of how big this
influence is. An HP3325 phase locked to an FTS1200 was used as the
generator in this ecperiment. For an comparison I add what a SR620 will
display in the same setup. All numbers are jitter in ps.

             
                      HP5370           SR620
-------------------------------------------------
Input voltage      Sine    Square   Sine   Square
-------------------------------------------------
4V pp              25.7     26.2     38     15
2V pp              23.8     26.4     50     20
1V pp              42.2     24.4     82     36
500 mV pp          83.6     51.9     200    70
250 mV pp          260      414      390    162

As you can see an comparison between the jitter indications of different
counters is not possible without exactly explaining the complete setup.

Best regards
Ulrich Bangert

> -----Ursprüngliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Dr Bruce Griffiths
> Gesendet: Sonntag, 10. Juni 2007 03:59
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] another Ebay mixup, 5370
> 
> 
> John Miles wrote:
> > Pretty similar results here, taken from the 5370B's 
> rear-panel output 
> > while running on the internal 10811B (attached).  Indicated jitter 
> > with this setup is about the same as it was on the ext ref via the 
> > 5087A (10-12 ps).
> >
> > I've seen this counter return self-test jitter results in 
> the 15-25 ps 
> > range before.  Not sure why it's in such a good mood today.
> >
> > At any rate, it doesn't appear that the wave shape is a 
> problem... but 
> > of course, you will usually get better jitter readings with a fast 
> > edge than with a sine wave.
> >
> > -- john, KE5FX
> >
> >   
> John
> 
> My 5370A currently has the following characteristics:
> With the EXT 10MHz connected to the input jitter is 15ps.
> With an FTS1200 5MHz input signal jitter is 46ps.
> With an external GPS locked 10MHz input signal jitter is 45ps.
> 
> This illustrates the danger in believing the jitter measured with a 
> coherent input signal.
> 
> Bruce
> 
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