[amsat-bb] Re: L Band Uplink Ant

[Wayne Estes]

John Wilcox / NS1Z wrote:
 > I don't think this statement is true. For very low wind speeds you
 > might be right. However, once the wind reaches a certain speed (one
 > which would exert moderate force) the mesh dish no longer will pass
 > the wind thru the small openings of the mesh. Due to surface
 > turbulance etc the mesh dish would appear to be solid and no air would
 > be passing thru it.

Wayne replies:

I built my Teksharp 4-foot dish kit with 1/4 inch hardware cloth which 
is 80-90% holes.  Other people estimated that it has about half the 
windload of a solid dish in a very high wind, which would be slightly 
less than the wind load of a 3-foot dish.  Anecdotally, people have 
reported that it's still extremely windy when they stand downwind of the 
dish in a gale force wind.  The dish would behave more "solid" in high 
winds if it was built with window screen or perforated metal instead of 
hardware cloth.

 > If the surface holes are larger (than the typical C/Ku dish) then the
 > air once again can pass thru at a higher wind speed. However, this
 > limits the dish usefulness since increased diameter surface holes
 > lower the useable frequency of the dish, something about a waveguide
 > beyond cutoff.

The Teksharp dish isn't intended for higher microwave frequencies 
because of the 8-petal design isn't a precise parabola.  And of course 
at higher frequencies you would need a finer mesh than 1/4 inch hardware 
cloth.  I wonder if the 4-foot Teksharp 8-petal dish can match the gain 
of a perfectly shaped 2-foot dish at 5 or 10 GHz?  That would still be a 
lot of gain.

Wayne Estes W9AE
Oakland, Oregon, USA, CN83ik