[time-nuts] To use or not to use transmission line splitters for GPS receivers

Hal Murray hmurray at megapathdsl.net
Wed Oct 10 21:59:13 EDT 2012


magnus at rubidium.dyndns.org said:
> I do know those that temperature stabilizes both the concrete  pillar and
> cable conduct.

I hadn't thought about the support pillar.  CTE of concrete is 8-12 PPM/C, so 
a 10 C change would be 100 PPM.  10 meters would be 1000 micrometers or 1 mm. 
 I think that's 3 picoseconds.

I couldn't measure that, but I expect it's important for the big boys.

I was thinking of 10 meters as being the height of a building.  A stand alone 
pillar in the middle of a field wouldn't need to be that tall.  The cable to 
the lab would be longer, but you could run two cables and measure the length 
of the other one with TDR.

I was thinking of a pillar as primarily in the vertical direction so maybe it 
doesn't matter as much.  But if it's on the corner of a building, maybe the 
whole building shrinks/grows in the horizontal dimensions too.  Most 
buildings are more than 10 meters long, but the temperature on the inside is 
usually constant so maybe the building doesn't change size much in any 
dimension.

What's the temperature time constant of a building or (unheated) antenna 
pillar?  What's the skin depth at 24 hours or 1 year?

(Steel is the same ballpark: 14 PPM/C)


-- 
These are my opinions.  I hate spam.







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