That's exactly what I setup at one company. Choke ring style GPS
antenna on the roof. 30dB amp inside the antenna. About 150ft of
LMR-240 coax. I used a power splitter and an AGC controlled amplifier
on the test line with a switchable RF attenuator to control the signal
level. L1+L2+WAIS patch antenna radiator under the test fixture to
minimize leakage to other test stations. I originally installed a GPS
bandpass filter to eliminate potential LightSquared interference but
that proved to be un-necessary and was removed. The building was
fairly well shielded as long as the doors and windows were closed. I
also installed a DGPS LF receiver and distribution system on the test
line, but since that dramatically increased the test time and few
users need DGPS, someone wisely decided that sample testing was good
enough.
The key part of the puzzle was the LMR-240 coax and associated
amplifiers. Any leakage from the coax or the amps would screw up the
test measurements. The switchable RF attenuator produced signal
levels down to about -145dBm, which could not be seen by any piece of
test equipment available. Typical operating levels at the receiver
input were about -135dBm. Watch your shielding carefully. However,
if you don't want to deal it, there are shielded boxes that will work.
<
http://www.rfshieldbox.com>
The GPS location indicated by such a system is the location of the
rooftop antenna, which was surveyed to an accuracy where continental
drift became part of the reference position calculation. With DGPS
active, the largest errors came from the phase errors of the rooftop
antenna measured in mm. You could sorta see earthquakes and
subsidence when big heavy trucks arrived at the loading dock.
Also, I recommend you get a GPSDO (GPS Disciplined Oscillator) to run
the test equipment clocks. Some early head scratching and weirdness
was eliminated by syncing everything to a common frequency (and
phase).
There was some mumbling about a NEMA-0183 simulator. This can be
easily done with a computah and commonly available GPS test programs.
<
http://avangardo.com/software/gps-generator-pro.html>
<
http://sourceforge.net/projects/gpsfeed/>
etc... Google for "NEMA test generator". Someone else scribbled a
test program based on gpsfeed+, which included simulations of radical
position excursions, reflection simulation, leap second function,
random garbage, loss of signal, and other oddities difficult to test
with a live GPS signal.
Good luck.
--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558