If you are talking about elevated radials, they have to be tuned for each
band at a 1/4 wave. At the very minimum you need two for each band (on
opposite sides of the "circle"). The higher you get the vertical (up on a
pole), the better those limited number of radials will work. I have always
used 4 in my setups and for forty meters, I was up about 15'. The antenna
worked VERY well.
The closer to the ground you have the vertical, the more poorly the elevated
radials work, necessitating more of them. With good ground, and ground
mounting the vertical, you can get very acceptable performance with 16
radials 50' long (80m). While this sounds like a pain...it's not, you can do
a temporary setup using nothing more than lawn staples in about 15 minutes.
The radials are non-resonant
Try this:
Lawn staples (from DX Engineering, very cheap). Buy a 500' role of THHN #14
insulated wire from your local hardware megastore, divide the wire according
to how much space you have, but don't exceed about 50' each. Use one staple
on the end, one in the middle. Just lay them on the ground, stretched tight
to prevent tripping. This would give you 10 radials, not a bad compromise.
Get another roll of wire if you want to do more and a little longer. 60 x 16
= about 1000'.
Fastening a wire to the base of the ground mounted vertical and stretching
it on the ground out takes a few seconds. Whack the staple with a light
hammer to pin the wire to the ground. Doing even 16 of them takes just a few
minutes. With good ground, you will have better than 70% efficiency with 16
60' radials.
Now...back to your elevated radials:
With a low mount (under 20'...probably under 40') the elevated vertical is
not going to be particularly efficient with only 2 tuned radials per band.
Also, getting them properly tuned is a pain and having them not tune, makes
them radiate (which on FD may be a good idea).
Wierd idea #3
Use only one elevated tuned radial per band, and it will radiate like crazy
at high angles (you now have an L shaped antenna on each band). This might
also be good for FD.
Have fun!
73,
...hasan, N0AN
----- Original Message -----
From: "Tom Osborne" <w7why@verizon.net>
To: "Towertalk" <towertalk@contesting.com>
Sent: Tuesday, June 13, 2006 11:50 PM
Subject: [TowerTalk] Radials
> Hi all
>
> Going to put up a 40/20 (probably use the 40 on 15) multiband vertical for
> field day.
> Do they work better with 1/4 radials for each band, or would 1/4 wave
> radials for 40 work on 20 OK? 73
> Tom W7WHY
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|