[time-nuts] GPSDO vs Rb standard

Bob Camp lists at rtty.us
Thu Sep 19 00:22:27 UTC 2013


Hi

The Rb's have a couple of issues:

1) Its been years since they were set on frequency and they do have a yearly drift rate
2) They have a temperature coefficient of drift that may be fairly large (0.1 ppb over -30 to +70)
3) They self heat quite a bit, so they do move temperature / need a heatsink

The solution to the temperature issue is a servo controlled fan. The solution to the first drift / accuracy issue is to calibrate them against something else.

Bob


On Sep 18, 2013, at 7:13 PM, "John C. Westmoreland, P.E." <john at westmorelandengineering.com> wrote:

> Azelio and Fellow Time Nuts,
> 
> Isn't the GPS 1PPS signal supposed to be 'precise' to within what error?  I
> imagine this is in the specs of the specific receiver -
> but I was wondering if some of you have actually measured what that is -
> and could report the numbers that you have found.
> 
> Thanks!
> John Westmoreland
> 
> 
> 
> On Wed, Sep 18, 2013 at 3:07 PM, Azelio Boriani <azelio.boriani at screen.it>wrote:
> 
>> Instead of using the Rb's PPS, use the GPS receiver's PPS. Maybe you
>> will find out that the Rb is slow... you can also check the Rb's PPS
>> against the GPS's PPS.
>> 
>> On Wed, Sep 18, 2013 at 11:47 PM, Bob Stewart <bob at evoria.net> wrote:
>>> I hooked the Rb's 1PPS to the trigger input on my old Tek 455, 10MHz
>>> GPSDO to Channel A, .05us trace, and turned the lights out so I could
>>> see it.  The 10MHz is marching right to left about 1 cycle every 20
>>> seconds.  So, can I say that the Rb considers my GPSDO to be too fast by
>> about 5ppb?
>>> 
>>> 
>>> Bob
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