[time-nuts] A counter for phase measures

[Bob Camp]

Hi

The 620 is still pretty good (when tuned up). It certainly beats the Pendulum's on a single shot basis. The 53230 is spec'd to be as good as the 620. I suspect it meets or exceeds it's stated specs.

Bob

On Nov 3, 2012, at 12:58 PM, Tom Knox <actast at hotmail.com> wrote:

> 
> 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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