Hi Tom,
I think we are in agreement here. But as I read your post
exactly what you meant was unclear to me (and probably to
others). I think you said (and meant) that compared to a
sufficiently dense screen in all directions from the antenna, an
antenna with just a sector screened would have lower efficiency
in all directions. I aggree with this interperetation.
But without the qualification, it could be construed to mean that
compared to an antenna with no (or very few) radials, the one
with a sector of ground screened to full density would have lower
efficiency in all directions. I don't think that is the case. I
think it would (absent radiation from the screen) have higher
efficeincy in all directions (screen too small to affect TOA).
But it would obviously have lower efficiency than one over a full
circle screen.
Am I interpereting your statement incorrectly?
73, Eric N7CL
>From: "Tom Rauch" <w8ji@contesting.com>
To: <towertalk@contesting.com>
>Date: Tue, 30 Mar 1999 06:34:08 -0500
>
>> HI, Does anyone have any field strength data, re the lowering
>> of radiation angle in a given direction if extra radials are
>> concentrated in that direction. ie taken to the extreme 60
>> radials covering 180deg whether that arrangement would have
>> the performance of 120 radials at the mid way point,and the
>> radiation angle increasing as you run out of radials. 73 Clive
>> GM3POI
>
>You might ask on rec.radio.amateur.antenna I think it is N6RK
>who actually measured this stuff, and his measurenents agree
>with theory.
>
>Theory tells us the radials do nothing at all for low wave angle
>performance unless they are several wavelengths long and very
>desnse (about .05 wl spacing) at the open ends.
>
>Also, if you concentrate radials in one hemisphere efficiency in
>EVERY direction drops.
>
>I found that true at WAAM radio, where someone cut and removed
>all radials going in the direction of a desired null. The only
>result of that was a decrease in field strength in all
>directions and instability of the array with soil moisture
>changes.
>
>73, Tom W8JI
>w8ji@contesting.com
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|