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

[TheInfamousFlavio at hotmail.com]

I read the same spec on pg 63 but I read it as a fluctuation not an offset.

I'm curious if you try the test Bruce suggested and set the gate time to 
0.1s and then 0.01s and see if the offset increase by a factor of 10 for 
each change?

I'm finding it hard to believe that this top of the line instrument can't 
handle this rudimentary task when my old Fluke 6680 with 500ps one shot 
precision (25 times slower than the SR620)  handles it perfectly.

I'm still not buying this offset is correct.


----- Original Message ----- 
From: "Robert Crawford" <avitek at wwnet.net>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Wednesday, February 21, 2007 23:13
Subject: Re: [time-nuts] SRS SR620 External Source Issue -- Help Request


>I ran into this same problem with my first SR620.  I thought it was
> defective, so I sent it to SRS for a cal and refurbishment.  It got
> better, but still had an offset of 0.0004 Hz.  Later I bought a second
> one, and it, too, had an offset similar to yours.
>
> A careful reading of the manual, page 63, Performance Tests, Accuracy
> (where the 10 MHz output from the back panel is measured at the A input)
> reveals that a +/- 0.0035 Hz offset on a 10 MHz input is acceptable and
> within spec.  I think this also applies to your test configuration.
>
> I have a photograph of my two SR620s, both using an external clock
> (PRS-10/GPS from an FS710 Distribution Amp), and both measuring the same
> signal on their A inputs.  One reads 10,000,000.00096 Hz and the other
> reads 9.999,999.99827 Hz.  I used a gate time of 1 second averaged for
> 100 readings.  Both SR620s had fresh factory calibrations.
>
> Bob Crawford
>
> 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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