Re: [amsat-bb] Trees and antennas and stuff

[Jonathan Naylor <jonathan.naylor@xxxxxxxxx>]

Hi Jim et al

>  As the wavelength become a significantly small fraction of the
> openings in the screen used for a Faraday box  other things happen, 
> diffraction begins to take place.  I doubt whether this has a chance
> of happening with trees as there are many, many layers of natural
> screens.

It all depends on the tree, Firs are instant death for signals. However 
less dense trees are not so bad, and I am able to operate 10 GHz 
through some local trees, I don't know the type but you can see through 
them quite well and the signals do also.

>  I recall the difficulty radio astronomers have when the spacing
> between rain drops approximates the wavelength of the signal desired
> to be detected.  This is different than the Faraday Box, but what
> about the size of a wet leaf (hundreds of wet leaves) as compared to
> that wavelength of a 2.4 Ghz signal ???

The problem with rain and rain on leaves are two seperate issues. The 
one I am familiar with is with rain on its own, and that really only 
becomes a big issue around 10 GHz. The weather radars operate around 
this frequency and we amateurs use heavy storm rain to bounce our 
signals off in the summer, so called Rain Scatter. Ranges up to 1000 
kms have been worked on this mode. For exactly this same reason storms 
that pass through the beam of a typical 11/12 GHz TV satellite system 
cause intense disruption to the signal.

>  Jim Jipping,  W8MRR
>  AMSAT 5512.

Jonathan  HB9DRD/G4KLX
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