[time-nuts] multipath on GPS

Chris Albertson albertson.chris at gmail.com
Sat Aug 9 10:40:37 EDT 2014

My experience with radar tells me it depends a lot on the geometry.  For
example a perfectly flat mirror-like reflector would only give trouble for
an instant when the angle was "correct" It would give very bright
reflection but then the satellite would move and then it would give no
reflection.    On the other hand a corrugated steel roof with all those
bends reflects over a very wide angle but it is not nearly so bright.

As an example from radar.  A small corner cube reflector made from straight
metal parts can be as bright as an oil tanker ship facing head on.  One is
only a couple feet wide and the other is hundreds of feet wide.
So the trouble with the rule you are looking for is that you have to
multiply the number of square meters by some factor that varies over
several orders of magnitude and then apply the inverse square law to
account for distance.   It's that darn factor that can't be estimated well.

If you are trying to site a GPS antenna.  Buy a 1" iron pipe and a 1" pipe
flange.  The flange provides a flat mounting surface for the antenna and
the wires can fit neatly inside the pipe.   I found with my timing antenna
that the bolt pattern on the bottom exactly fit a standard pipe flange.
 Perhaps not by coincidence.

On Fri, Aug 8, 2014 at 12:39 PM, Jim Lux <jimlux at earthlink.net> 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?
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Chris Albertson
Redondo Beach, California

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