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

[TheInfamousFlavio at hotmail.com]

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" <avitek at wwnet.net>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
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
>
>
>
> TheInfamousFlavio at hotmail.com 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" <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.
>>>>
>>>>_______________________________________________
>>>>time-nuts mailing list
>>>>time-nuts at febo.com
>>>>https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>_______________________________________________
>>>time-nuts mailing list
>>>time-nuts at febo.com
>>>https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>
>>>
>>>
>>
>>
>>_______________________________________________
>>time-nuts mailing list
>>time-nuts at febo.com
>>https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>
>>
>>
>>
> _______________________________________________
> time-nuts mailing list
> time-nuts at febo.com
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>