Roger (K8RI) wrote:
>
>
>>>> 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.
As far as propagation through the air/over edges goes, your radio signal
is monochromatic.
And, it's only one ray that's propagating from here to there. Yes, you
launch many rays, but most don't go to there. So, it still does work.
Multipath does occur, but each of the individual paths is reciprocal at
any given instant. They just change relative to each other
(particularly on skywave) so you get frequency selective fading.
>
> That is where I have a problem with understanding recriprocity on the signal
> path.
You along with the rest of us. Maybe what we need is one really good
explanatory example..
>
> Roger (K8RI)
>
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