[time-nuts] Cs stability
Dr Bruce Griffiths
bruce.griffiths at xtra.co.nz
Tue Jul 17 05:30:03 EDT 2007
Tom Van Baak wrote:
>> I guess that is why some GPS antenna cables is temperature-stabilized as well
>> as the cement-pidestal for the GPS antenna as it stands on solid rock. The same
>> place have controlled environment for the cesiums and hydrogens, together with
>> UPS and disel-engine that kicks in for longer runs.
>> Or I could be wrong... :)
> This is true (temperature stabilization) for sites that do mm
> level survey and ps level time transfer, using all the tricks
> in the GPS book.
> On the other hand, I think for most of us that play at the
> meter and ns levels with cheap OEM receivers and plastic
> L1 antennas the coax cable temperature issue is quite
> overblown. Or if I'm wrong, show me the data.
Calculations are easy:
Cable delay tempco is at worst 100ppm/K.
with 100ns of cable delay tempco will be 10ps?K or less.
With a 20K temperature change change in delay will be 200ps or less.
The group delay tempco of the antenna components (bandpass filters
amplifiers etc ) is likely to be much greater.
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