What about using cables to simulate the reflector? Connecting the
antenna to the receiver using a splitter, two very different length
cables and then a combiner at the receiver's input.

On Fri, Aug 8, 2014 at 9:39 PM, Jim Lux jimlux@earthlink.net wrote:

Jim,

On 08/08/2014 09:39 PM, Jim Lux wrote:

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

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@rubidium.dyndns.org wrote:

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@earthlink.net wrote:

--

Chris Albertson
Redondo Beach, California

On Fri, Aug 8, 2014 at 2:52 PM, Azelio Boriani azelio.boriani@screen.it wrote:

That is a very unrealistic test.  True reflections would come from
only those satellites that were in the correct geometry and the path
length would be different for each of them and this all would change
over time.

--

Chris Albertson
Redondo Beach, California

Hi

…. back to “that depends”….

When you have a sat at just the right point and you are tracking that sat and it’s a significant part of your solution - you get a multi path issue. Then the question becomes how good your particular receiver is at rejecting multi path.

You can indeed do a pretty good job reflecting GPS with a 1 meter square sheet. I ran the experiment with a 1/6 size sheet and 6X the frequency. You can get a good signal with the right geometry. No I don’t have any exact data. I ran it back in microwave lab back in school … hopefully the physics of microwave reflection hasn’t changed much in 40+ years.

Bob

On Aug 9, 2014, at 10:44 AM, Chris Albertson albertson.chris@gmail.com wrote: