[time-nuts] GPS antenna question

[Robert DiRosario]

If I want to use GPS for time and frequency standards, just how solidly 
does the antenna need to be mounted?
The easiest and least expensive way to mount a GPS antenna would be up 
on two 10' TV mast sections, but that
would move around a bit in the wind.  Maybe two or three inches.  Or do 
I need to do better?  All of the "easy" or
"good" spots in my yard already have amateur radio antennas.

A second question, and it may very between different GPS receivers, how 
to they get the time?  Do they just take one signal
with a good S/N number and correct for the distance from that satellite, 
or do something more complicated with several signals?

Thanks
Robert