I am converting a RS FM ant into a 2m yagi per the article. I have
worked out a way to flip flop the antenna from vertical to horizontal
and back as I like, but am concerned about interference from my 20
foot 'tower' when in horizontal mode, it being emt. Would some kind of
shielding on the emt work to prevent problems? Or would it even be
enough of a problem to worry about?
Thanks for any help!

On 8 Nov 2003 13:12:25 -0800, wrote:

I am converting a RS FM ant into a 2m yagi per the article. I have
worked out a way to flip flop the antenna from vertical to horizontal
and back as I like, but am concerned about interference from my 20
foot 'tower' when in horizontal mode, it being emt. Would some kind of
shielding on the emt work to prevent problems? Or would it even be
enough of a problem to worry about?
Thanks for any help!

I think you meant interference in the vertical position. About the
only way to prevent interaction is to use a non-conductive mast such
as fiberglass. Placing a non-conductor over the emt wouldn't help
much, if any, so it's probably not worth the effort. You may notice
change in SWR and you can expect a change in radiation pattern
-however it may not have a significant impact on performance for local
and/or repeater use.

wrote in message
om...
I am converting a RS FM ant into a 2m yagi per the article. I have
worked out a way to flip flop the antenna from vertical to horizontal
and back as I like, but am concerned about interference from my 20
foot 'tower' when in horizontal mode, it being emt.

Would some kind of shielding on the emt work to prevent problems?

I can think of ways to make the EMT not reflect, but they would also make it
absorptive, which would also be not good.

Fiberglass pole is pretty much the only way to be sure it dosen't interact.

You have me interested though, what mechanism are you using?
I've toyed with some ideas, but never hit anything I liked.
I thought about using a crossed yagi, but that gives me a 3db penalty in
both modes. :-P
Also, birds and ice love horizontal elements. I'd like to be able to go
horzontal, but stow it vertical to avoid those hazards.

"Dave VanHorn" wrote in message ...
wrote in message
om...
I am converting a RS FM ant into a 2m yagi per the article. I have
worked out a way to flip flop the antenna from vertical to horizontal
and back as I like, but am concerned about interference from my 20
foot 'tower' when in horizontal mode, it being emt.

Would some kind of shielding on the emt work to prevent problems?

I can think of ways to make the EMT not reflect, but they would also make it
absorptive, which would also be not good.

Fiberglass pole is pretty much the only way to be sure it dosen't interact.

You have me interested though, what mechanism are you using?
I've toyed with some ideas, but never hit anything I liked.
I thought about using a crossed yagi, but that gives me a 3db penalty in
both modes. :-P
Also, birds and ice love horizontal elements. I'd like to be able to go
horzontal, but stow it vertical to avoid those hazards.

Dave,
Just have it on a small hinged wood platform, one side on the mast,
the other side on a separate support forming a very narrow 'y' going
down to a cup support at ground level. normal postion would be up, for
vertical ops, just lift up (and out of the cup) and let it drop down.
Some details to work out, but it should work.