[time-nuts] A counter for phase measures

Tom Knox actast at hotmail.com
Sat Nov 3 16:58:39 UTC 2012


Hi Magnus;
I hope this is not to far off thread. Has anyone in the group done real world measurements of single shot res, and jitter on the new Agilent and Tektronix/Pendulum counters compared to the SR620 and Agilent 53132A. I would imagine that counter designs would be an area that really benefits from ongoing advances in digital technology.  I have also found that it is much easier to claim specs then meet specs.
Thanks;
Thomas Knox



> Date: Sat, 3 Nov 2012 16:28:42 +0100
> From: magnus at rubidium.dyndns.org
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] A counter for phase measures
> 
> On 11/03/2012 03:10 PM, Volker Esper wrote:
> >
> > Thank you for the interesting information. Now, the time has come to
> > look for an adequate counter - anyone who has experience with the HP
> > 53132A and the SR620? If they both where at - say 1000 USD - what would
> > you prefer for the job of phase measurement? I've read about that
> > massive single shot capability of the SR, but - as being a newbie - is
> > there anything I overlook at this moment?
> 
> For short time-scales, single shot resolution and trigger jitter 
> dominates your measurement floor.
> 
> Single-shot resolution is the time resolution by which you make a single 
> measurement.
> 
> Trigger jitter is the noise at the trigger point. it's a combination of 
> thermal noise and the slew-rate at the trigger points. It is often that 
> trigger jitter is dominated by slew-rate, but there is also internal 
> sources of trigger jitter. The slope dependent trigger jitter follows 
> the formula:
> 
> t_jitter = v_noise / s_slew
> 
> t_jitter is the trigger jitter (s)
> v_noise is the noise power (V)
> s_slew is the slew rate (V/s)
> 
> When the time-span of a measurement is long, long-term stability comes 
> in as well as systematic drifts. Also, systematic noise such as hum also 
> becomes important.
> 
> To see how much you depend on slew-rate limitation, you can reduce the 
> amplitude, and as this reduces the slew-rate you can separate the 
> slew-rate dependent jitter from the intrinsic jitter of the input. It 
> also helps you to identify if you need to work on the slew-rate limit 
> rather than anything else.
> 
> So, it may not be the single-shot resolution which limits you, but a 
> combination of things.
> 
> I would recommend you to pick up a SR620. It has 4 ps single shot 
> resolution and about 25 ps jitter (but you can get less). That is 
> significantly better than the 53152A provides.
> 
> SR620 manual (one of many links):
> http://ilrs.gsfc.nasa.gov/docs/timing/sr620_manual.pdf
> 
> Cheers,
> Magnus
> 
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