On Sun, 30 Nov 2008 23:55:02 GMT, wrote:

Richard Clark wrote:
On Sun, 30 Nov 2008 21:45:03 GMT, wrote:

Art Unwin wrote:
Since we are at the low sun cycle I shoose
1" hexigon poultry wire for the mash on my 3 metre dish
At what frequency will there be a noticable effect on aperture
starting with top band?
Many thanks
Art KB9MZ...,XG

The rule of thumb is things less that .1 wavelengths in size have
negligable effects, so roughly up to about 1 GHz.

Hi Jim,

You neglect to mention that a 3 meter dish would be wholly (no pun
intended) transparent to RF in the top band. It could be solid metal
to no notice by a radiator (or receiver).

It would be like blocking the sound 3 feet from the stage at a Led
Zepplin concert with a Japanese parasol. -Huh?-

73's
Richard Clark, KB7QHC

Yeah, I foolishly forgot the source of the question and assumed "top
band" meant highest useable frequency.

Unless I hosed the math, a 3 m dish would be a little over 10 db
isotropic at 2 m, so the combinatation would "work" from 2 m to 23 cm.

Well, if you take the question literally, the aperature of a 3 meter
dish is ummm.... 3 meters. If he had said effective aperature, the
answer might be different.

As for top band (160 meters), he might be referring to a chicken wire
ground. This looks marginally applicable:
http://lists.contesting.com/_topband/2002-09/msg00005.html

Maybe he's thinking of burying his 3 meter dish and using it as a
ground radial system?

Incidentally, I've had rather bad luck using twisted galvanized
chicken wire for making dish antennas. I kept getting intermittent
noise crashes and arcing like noise bursts on a 1.7GHz WX satellite
system I once threw together. I eventually found that banging on the
chicken wire would produce the same noise bursts. I didn't bother
trying to find out exactly what was doing the arcing. When I switched
to using aluminum flashing and aluminum duct tape for the reflector,
the noise went away.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558