[time-nuts] A counter for phase measures

[Bob Camp]

Hi

There is a fairly elaborate alignment procedure for the 620. It's been reported in great detail here on the list. The counter definitely does better after you go through the full process.

Bob

On Nov 3, 2012, at 3:42 PM, Volker Esper <ailer2 at t-online.de> wrote:

> 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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