[time-nuts] multipath on GPS

Magnus Danielson magnus at rubidium.dyndns.org
Sat Aug 9 04:20:13 EDT 2014


Jim,

On 08/08/2014 09:39 PM, Jim Lux wrote:
> Does anyone have a feel for what the minimum size reflector at some
> small distance would be detectable on a GPS timing receiver? WOuld you
> be able to see a change of a 1 meter square reflector 10 meters away?

It depends. Your question is radio-oriented rather than GPS oriented. 
The radio-question has a relative straight-forward answer, as the 
ste-radian of the reflecting surface as seen from the GPS antenna is 
relevant, as is the effective part of the reflecting surface, the part 
which provides the right reflecting angle. If you have a multipath 
damping antenna such as a choke-ring or pin-wheel antenna, that 
naturally affect things, as susceptability becomes ever more dependent 
on the incoming angle. The angle of the satellite itself is another 
radio-side aspect, as it will effect the geometry and the reflection can 
become less effective for another angle.

However, the distance from the antenna also adds delay, and the added 
path delay will affect the GPS receivers sensitivity to multipath. It 
also depends on using the C/A signal or using the P(Y) signal, the C/A 
signal correlator distance, the bandwidth of the receiver front-end 
(narrow bandwidth does not work well with narrow correlators). Also, the 
effect also depends on wither you use code or carrier phase.

As you see from the above, there is a lot of parameters in the "It 
depends" and I think you might need to narrow down the question by being 
more specific.

I good aimed 1 meter square reflector at 10 meters, may or may not be 
detectable, depending on how good or bad receiver and antenna you have.

Cheers,
Magnus


More information about the time-nuts mailing list