[Wswss] [PNWVHFS] 1296 dish

[Jim Garver]

Aerodynamically, it doesn't matter what size holes until extreme.  

Above a certain speed, the dish looks solid to the wind due to turbulence
through the holes, around the wires or mesh.   That speed is fairly low.

 

>From memory, hole size should be .1 wavelength or less.  I remember it was
max ¼" dia. @ 4 Ghz for TVRO.

 

What is your feedhorn?  Do you know the illumination angle, coverage?
Much of the area is often wasted.

 

I have a 10' Channel Master TVRO dish.  They were very good for TVRO, with
low side-lobes.  Tiny holes however.    More gain can be had with a shallow
dish - high F/D ratio.  Not good for TVRO, side-lobes from high gain dishes
pick up co-channel interference from adjacent satellites.   Still, some of
the early mesh dishes like Paraclipse had high F/D.  And they were big, too!

 

K7YO

 

From: pnwvhfs at googlegroups.com [mailto:pnwvhfs at googlegroups.com] On Behalf
Of Len Gwinn
Sent: Sunday, September 06, 2009 6:03 PM
To: wswss at mailman.qth.net; PNWVHFS; vhf at w6yx.stanford.edu
Subject: [PNWVHFS] 1296 dish

 

Hi all,

 

I have been using a 10 foot TVRO dish on 1296.  It works great BUT BUT,  I
have a question.

 

Situation.---The dish presently has small spaced wire mesh for its surface.
OK, that is smooth.  BUT when I get high winds it is more like a solid
surface I have been told.  I am getting some structure damage from the high
wind vibration where the dish is braced back into the house at the center of
the dish.  I have tried turning the dish sideways into the wind but no
change in conditions.  Wind in the winter runs up to 70 mph  !!

 

Question---How much do I lose in gain--if at all--if I change the dish
surface to half inch hardware cloth/wire/screen,   OR to one inch similiar
material???  This should greatly cut down any vibration/acting like a solid
dish ie, wind load would be much much less.  Does this also maybe allow more
power to go thru the dish thus affecting anyone behind the dish  ???

 

I am planning on moving up to 300 watts output to the dish and would rather
use the dish than a 22 element beam !!!

 

Any ideas or help  ?? or places to go read about it  ??

 

Thanks

 

Len  WA6KLK


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