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

TheInfamousFlavio at hotmail.com TheInfamousFlavio at hotmail.com
Thu Feb 22 14:59:54 UTC 2007


1.  Same test with a Fluke 6680 yeilds 10MHz mean exactly.

2.Tried different length cables and swapping the cables.  Same result.

3. Autocal was done (a few times)



----- Original Message ----- 
From: "Tom Van Baak" <tvb at LeapSecond.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Thursday, February 22, 2007 00:12
Subject: Re: [time-nuts] SRS SR620 External Source Issue -- Help Request


> >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.
>
> Three comments that may help.
>
> (1)
> 0.0015 Hz out of 10 MHz is 1.5e-10 which seems a little
> high but not too bad. But do not expect exactly 10 MHz with
> this sort of "test". What you are giving to the channel A
> input is the most highly phase correlated signal you can
> imagine relative to the internal clock and the interpolators.
> This won't happen in real life with real input frequencies.
>
> (2)
> Try different lengths of the channel A cable and see if the
> number changes. My prediction is it will.
>
> (3)
> Run the setup menu self-calibration if you haven't in a while.
>
> /tvb
>
>
>
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