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Old July 15th 03, 02:16 AM
Richard Harrison
 
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Floyd Davidson wrote:
"But, it doesn`t emulate "a satellite" shot in the slightest."

A satellite is a microwave repeater in the sky which is usually not
susceptible to earth reflections.

Terrestrial microwave paths are often designed to minimize earth
reflection.

Reason is, on a long path, the lengths of the direct ray and the Earth
reflected ray are almost the same. Reflection reverses the phase of the
reflected ray so that the reflected ray detracts from the direct ray
when they combine at the receiver. They arrive out-of-phase, at least at
some antenna altitudes.

The phase of the signal undergoes 180-degrees of phase change as we
examine the signal either forward or backwards from the plane of the
signal. That is to say, the phase of the signal is a function of
distance along the path. When a second signal source is created by Earth
reflection on the path, the combination of the direct and reflected rays
produces strata of stronger and weaker signal intensities as altitude
changes. No reflected signal, no significant variation of signal with
altitude, given sufficient path clearance. This is a worthwhile design
goal.

No matter which end of the TV relay path was varied to produce a
significant signal strength change, the attenuation at the higher
elevation was probably caused by an Earth reflection. Another reflecting
surface near the microwave path could have been the reflector. I`ve seen
that in the city canyons I`ve had to squeeze signals through. But on
most paths, the Earth is the most likely reflector.

Best regards, Richard Harrison, KB5WZI