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

Mike Fahmie mpfahmie at lbl.gov
Wed Feb 21 18:50:59 EST 2007

At 02:57 PM 2/21/2007, you 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.

Perhaps you're running into some sort of meta-stability problem since your 
clock and input are synchronous. Try lengthening one of the cables a foot 
or so and see if it makes any difference.

Also, it could be the compound result of noise in both the reference input 
and signal input amplifiers.


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