Bob, I see what your saying about the frequency error spec on pg vii, but I'm still reading as a fluctuation not an offset of the mean. In my mind, I don't see why there should be some sort of adjustment for this. I really doesn't make sense that the would make a counter that doesn't display a mean that is accurate. -Flavio
----- Original Message ----- From: "Robert Crawford" <[EMAIL PROTECTED]> To: "Discussion of precise time and frequency measurement" <[email protected]> Sent: Thursday, February 22, 2007 11:58 Subject: Re: [time-nuts] SRS SR620 External Source Issue -- Help Request > Flavio, > > Your experience exactly parallels my surprise and disappointment when I > bought my first SR620. In fact, that's why I bought my second one: I > just couldn't believe the results, even though it had been freshly > calibrated by the factory. > > However, the Specifications on page vii of the manual tells the story. > The Frequency Error is listed as "< +/- ((100 ps typ) [350 ps max])/Gate > + Timebase Error) x Frequency". If you make timebase error zero and use > a 1 second gate, for a 10 MHz signal you get +/- 0.001 Hz, or +/- 0.0035 > Hz max. For a 0.1 second gate, the typical error goes up to 0.01 Hz, > which is exactly what you are seeing. > > I haven't played with the CALBYTE 4 value since I sent both of mine to > SRS for calibration. If I remember right you need to move a jumper > inside the unit to enable adjustment of this value, and I didn't want to > break the factory calibration stickers. I thought this was simply the > internal time base frequency adjustment. > > Bob Crawford > > > > [EMAIL PROTECTED] wrote: > >>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" <[EMAIL PROTECTED]> >>To: "Discussion of precise time and frequency measurement" >><[email protected]> >>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 >>> >>>[EMAIL PROTECTED] 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. >>>> >>>>_______________________________________________ >>>>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 >>> >>> >>> >> >> >>_______________________________________________ >>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 > _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
