[time-nuts] Delay through GPS antenna splitter/amplifier -- an answer, and a question

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Tue Mar 13 05:29:08 UTC 2007


Hal Murray wrote:
>>>> So the cable delay should be a multiple of 317.375...ps.
>>>>         
>>> What's the thermal coefficient of coax?
>>>       
>> Typically around 50-100ppm/C depending on the coax.
>> High velocity cables have lower tempcos
>>     
>
> Handwaving...
>
> 100 ft of cable is 70ns or 70000ps.
> 100ppm is 7ps.
> 10C is 70ps.
>
> So if you start out right, you will stay close but not right-on.
>
> I'm assuming the cable runs outside where the temperature isn't controlled.
>
> How much of your gear has a sticker on the front telling you how many ps 
> between the connector and the internal terminator?
>
>
>   
Hal

This is why the antenna and cable temperatures are regulated in some 
geodetic GPS stations.

Bruce




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