[time-nuts] A counter for phase measures

[Volker Esper]

Hi Bob

I didn't expect something to be tunable in the counter (except for the 
oscillator) - what is it that has to be calibrated?

Thanks

Volker


Am 03.11.2012 18:04, schrieb 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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>> 		 	   		
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>
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