>>>
>>> It seems to me that a good portion of Station B's signal arriving at the
>>> hill could overshoot Station A because it wasn't diffracted enough. The
>>> path taken by the signal from B to A would be identical to the path
>>> taken by the signal from A to B EXCEPT for the portion between Station A
>>> and the hill. Think directional coupler.
>>>
>
> Uhh, nope.. even though it sort of seems that way at first glance..
>
>
> Imagine that the top of the hill is a big lens or prism that bends the
> ray (which is what diffraction is, in one sense)..
>
> Launch a ray from A towards B and it follows a certain path, apparently
> bending over the top of the ridge. Some distance after the hill, stop
> the ray and send it back exactly as it came. When it gets to the
Unfortunately you are working with lots of rays. IOW Difraction causes a
bending AND spreading effect just as the crystal does. To end up where you
started you have to refract all of the rays, not just one. With the prisim
you have to refract the entire spectrum to get back to the original
composition. If the signal/light has spread far enough that the entire
composition can not be collected and refracted you can not get back to where
you started.
That is where I have a problem with understanding recriprocity on the signal
path.
Roger (K8RI)
> prism/lens it will bend it just like it did on the outbound trip and
> wind up at A.
>
> As long as there no nonlinearity in the system, it works.
>
> Where there IS non-reciprocal propagation you need something else. here
> are some examples:
> a) propagation through the ionosphere, which is anisotropic. The
> polarization is rotated by the Faraday effect, but the same rotation
> regardless of direction, so, if you have polarized transmit and receive
> antennas, oriented, say, 45 degrees apart, and the rotation is 45
> degrees, A signal from A to B winds up perfectly lined up, but a signal
> from B to A is cross polarized.
>
> b) the ordinary and extraordinary ray (polarization dependent) follow
> different paths, so when they combine the net effect is different
> depending on the direction (actually another case of the phenomenon in A)
>
> c) sound propagating in a medium with a velocity gradient. This causes
> sound to bend down when going downwind, and bend up when going upwind.
>
> d) various and sundry light propagation through various crystal
> phenomena (e.g. polarizers, birefringent materials, etc.)
>
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