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Dish az/el positioning: for Fred CU8AO



Hello Fred, your e-mail bounces,    unknown user:  fredf@clix.pt

Sorri to burden the rest of the Net.

Hello Fred,

also consider a signal source that you put in the far field, to verify 
antenna performance.
Far field is [ ( 2 times (D squared)) all over lambda],
D is the diameter of the dish.
Signals closer than the far field limits may not give the best test results.

A controlled CW signal source and controlled polarization 
is usually the best.

That way you can not only check the pointing accuracy but also if the feed
is positioned properly and polarization is correct.

Another method is to look at the depth of the "first null" which is 
usually very sharp, if you can find it.

On either side of the main lobe is the "first null", then the first sidelobe
 then a null, then the next sidelobe, then another null , etc.

The nulls may not be detectable due to antenna range (terrain) 
imperfections and other reflections.

If no nulls are to be found, look at the symmetry of the main lobe in az 
and el.

Then calibrate az and el to the maximum of the main lobe.

What size dish are you playing with ?  is it fed at the prime focus ?


Stan, WA1ECF   FN41sr





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