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Terry

Why dose a dish work ?

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Why is it that the signal that hits the centre of the dish and is reflected to the aerial dose not null out the signal that hits the dish at the edge ?

If there is a half wavelength difference in the distance the signal has to travel to reach the aerial it should, should it not ?

Terry

UK

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If the driven element is not in the focal region then you are correct. That issue is an advantage since out-of-phase signals are not coherent and do not properly reinforce each other. {A correctly designed dish puts the element at the proper focal region so that desired signals are not lost.}

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If I follow you correctly then what you are saying is if the dish is made right the signal will travel the same distance to the focal point no matter where the it hits the dish ?

Terry

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Thanks, thats a great link !

It dosent quite answer this particular point though. The point is that it is possable to make a dish that causes the signal to reach the focal point ok but at different times. Do you agree ?

Terry

UK

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The site states that "Poor antenna performance can result from inaccuracies in the dies used to manufacture the reflector surfaces."

A dish that was improperly made or installed would allow desired reflected signals to arrive at the antenna element at different times. If delayed enough, they can even cause a canceling affect. In other words, to achieve RF gain they need to be phase aligned.

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Ahh, thats what I was getting at ! Im not sure how many people realise that its not as easy as making a reflector for a headlamp. I didnt !!!

Thanks for helping me to get it strait.

Terry

UK

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