[time-nuts] A counter for phase measures

Volker Esper ailer2 at t-online.de
Sat Nov 3 21:29:31 UTC 2012


Great, your answere gives me hope, that the calibration procedure can be 
done at my home :-)

Thank you!

Volker


Am 03.11.2012 21:08, schrieb 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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