At 01:55 AM 12/9/98 +0000, Tad Danley, K3TD wrote:
>
>I am planning on installing an inverted L and have a few questions:
>
>1. As a connection point for the radials, radiator and coax cable, is
>there any advantage in using a 1:1 current balun, or should I just use a
>dipole center insulator? The radiator will be an insulated wire run as
>far up a tree as I can go vertically, then horizontally to another tree.
>
If you have a good ground (probably at least 30 radials) you will probably
need something like a 1:2 or 1:2.5 current balun to get a better match as
the impedance of the inverted L with a decent ground will be on the order
of 20 to 30 ohms. Many of us make our L's longer (150'-170' total H+L)
this brings the R portion R+jX closer to 50 ohms, then tune out the jX with
a simple series C of 200-500 pf. The longer top section gives some added
high angle radiation as well as low angle good all around 160 contest
antenna. A normal 1/4 wave L with the 12 radials you mention below will
be very close to 50 ohms and can be feed directly with 50 ohm coax.
For tree supports I use a rope passing through a pulley at the top of the
tree and about 20#'s of "ballast" to hold the antenna taught. That way when
the wind blows and the tree sways the rope will ride back and forth through
the pulley keeping a fairly constant tension on your antenna and not break it.
>2. I plan on starting with about 12 ground radials. Is there an easy
>way to get them to stay where I want them on the ground - like plastic
>staples?
I use large 7" nails, what is called in the trade a "gutter spike". (used
to nail gutters to the eves). One wrap of the radial wire around the nail
and drive it in the ground with a hammer. with 60 radials I use #18
insulated wire for radials.
By the way as you add more radials over time expect the resonant frequency
to creep up. So leave a couple of extra feet of wire wrapped back on itself
at the end insulator which will make lengthening the antenna easier later.
>
>Any and all suggestions and comments will be greatly appreciated!
>
>73,
>Tad, K3TD
>
>--
>Tad Danley, K3TD
>mailto:tadanley@mindspring.com
>
>TRA 4501, TARA 18, NAR 14020
>For amateur radio contesting try http://www.contesting.com
>For high power rocketry try http://www.rocketryonline.com
>
>
>
>--
>FAQ on WWW: http://www.contesting.com/topband.html
>Submissions: topband@contesting.com
>Administrative requests: topband-REQUEST@contesting.com
>Problems: owner-topband@contesting.com
>
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|