[time-nuts] SRS SR620 External Source Issue -- Help Request

[Dr Bruce Griffiths]

TheInfamousFlavio at hotmail.com wrote:
> I've done the self calibration. Nothing changes.  I've let everything 
> warm-up and checked both channels A and B, same thing.  I've swapped the 
> cables on the front and the back, same thing.  I've tried a T-connector on 
> the ref input with 50ohm termination, same thing.
>
> The readings are pretty stable, they are just offset by -0.0015 Hz.
>
>
>
>
> ----- Original Message ----- 
> From: "Brooke Clarke" <brooke at pacific.net>
> To: "Discussion of precise time and frequency measurement" 
> <time-nuts at febo.com>
> Sent: Wednesday, February 21, 2007 18:04
> Subject: Re: [time-nuts] SRS SR620 External Source Issue -- Help Request
>
>
>   
>> Hi Flavio:
>>
>> Have you tried using averaging?  The right most digits are from an
>> interpolator and if  you check the manual the displayed resolution is
>> much greater than the accuracy, but if you average say 1,000 readings
>> then those digits get much better.  Also have you done the self 
>> calibration?
>>
>> Have Fun,
>>
>> Brooke Clarke
>>
>> w/Java http://www.PRC68.com
>> w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
>> http://www.precisionclock.com
>>
>>
>>
>> TheInfamousFlavio at hotmail.com wrote:
>>
>>     
>>> I have an SR620 counter that I set up with a Z3801A as an external 
>>> reference.  If I put a bnc T connector at the output of the Z3801A and use 
>>> two equal length bnc cables, one to the ext. ref input on the back and the 
>>> other to channel A then do a frequency measurement, I get a mean that is 
>>> about .0015 Hz below 10,000,000.0000Hz.
>>>
>>> Does any know why this might be happening? I would expect it to read 
>>> 10,000,000.0000 exactly give or take a couple on the last digit.
>>>
>>> _______________________________________________
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>>>
>>>
>>>
>>>       
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>>     
>
>
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>   
Flavio

Your  SR620 is well within its specifications, the tolerance for this 
test is -0.0035 Hz to + 0.0035 Hz.

Bruce