On 7/31/2015 10:59 AM, Pawson, James wrote:
I can do this simply when the TX and RX antennae are the same height
above the reflecting surface as the point of reflection lies halfway
between the two antennae, Distance_tx = Distance_rx. The direct and
reflected paths can be calculated using simple geometry and the
wavelength is given by lambda = c / f.
However when the height of the RX antenna is different to the height
of the TX antenna then the horizontal distance to the reflection point
is no longer equidistant. I can see that the ratio Height_tx /
Distance_tx = Height_rx / Distance_rx remains the same because the
angle of reflection is the same. But I’m left with two unknown
Distance terms in the equation.
Why not reverse the problem?
You know the distance between antennas, and can set the height. This
creates a st of triangles consisting of a direct path and a reflected
path whose angle of reflection is equal to the angle of incidence, where
each end terminates at a source or an antenna.
Using the optical constraint re angle of reflection, generate a table of
triangles whose two ends terminate at these points and, with frequency
as an input variable, calculate for each one the frequencies where the
paths are either in phase or out by 180 degrees.
A quick way (IMO) is to just measure what happens. Using a swept signal
source and your normal setup, save the data, look for minima and maxima,
and filter the resulting data. If you've corrected for AF and cable
losses you're done.
Cortland Richmond
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