[Moon-net] [Mw] CIRCULAR / LINEAR POL ON 10 GHz EME

[Robert McGwier]

(Why am I getting involved with this? Sigh. )

Jerry:

This dish at Bochum is pretty large.

http://www.amsat.org/amsat/archive/amsat-bb/200406/msg00232.html

It is 20 meters.    In general, the beamwidth of an aperture that is X 
wavelengths in size is about 1/X radians or about 57/X degrees.

Let's call the beamwidth of 1.22/X radians = 70/X degrees. The 1.22 
number is often called the "Airy Criterion" (since this makes it larger).

So, depending on the illumination, the 20 meter dish at a wavelength of 
3 cm,  the quantity X is about 690 wavelengths wavelengths. Therefore 
the beam will be about

      (Airy criterion = 1.22)/(691 wavelengths) = .00183 radians = 0.1 
degrees.

which is less than 20% of the (typically used) 0.5 degree moon.   Paul's 
feed (in use at Bochum) will be assumed to be spectacular and we will 
take this number.   I suspect that reflections aimed at the "dark seas"  
which make up a large portion of the moon's visible face would scatter 
less and if the dish happened to be aimed at these smoother areas,  I 
would expect demonstrably less scattering.

SO,  I do not find this graph conclusive.  More experiments with smaller 
antennas showing a similar effect would be more suggestive.

Bob
N4HY




Jerry Kleker wrote:
> PLEASE RAINER, LOOK AT THIS PICTURE!
>  
> http://groups.msn.com/W7QX/10ghzemepolarizationtests.msnw?action=ShowPhoto&PhotoID=72 
> <http://groups.msn.com/W7QX/10ghzemepolarizationtests.msnw?action=ShowPhoto&PhotoID=72>
>  
> IF 10 DB IS MARGINAL TO YOU.........
>  
> 73,
>  
> Jerry    W7QX


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