[time-nuts] multipath on GPS

Azelio Boriani azelio.boriani at screen.it
Sat Aug 9 07:15:54 EDT 2014


To take out the reflection angle variation between satellite and
reflector, I think that using cables can help, so that it is possible
to experiment with the multipath sensitivity of the receiver. The
experiment then can continue using a real reflector. The satellites'
position is known and maybe this can be used in computations. At the
moment it seems an interesting experiment to me.

On Sat, Aug 9, 2014 at 10:20 AM, Magnus Danielson
<magnus at rubidium.dyndns.org> wrote:
> 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
>
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