[time-nuts] Substitute GPS in a Z3801A

Hal Murray hmurray at megapathdsl.net
Thu Jun 24 17:14:13 EDT 2010


rbenward at verizon.net said:
> What about the antenna cable length  compensation?  How much does that
> affect the AVAR?

The software in the GPS board can't measure the length of the antenna cable.  
If you don't correct for it, the PPS signal will be off by the speed of light 
delay.  That's (very) close to 1 ft/ns in air.  Coax is slower.  So with a 50 
foot cable your PPS signal would be off by over 50 ns.

If you are measuring AVAR, the cable delay just shifts everything by a 
constant so it won't change anything.

I've seen comments about very good setups being able to notice the change in 
antenna cable delay with temperature changes.  That might show up in AVAR.


-- 
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