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" <[EMAIL PROTECTED]> To: "Discussion of precise time and frequency measurement" <[email protected]> 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 > > > > _______________________________________________ > time-nuts mailing list > [email protected] > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
