Gregg, et. al.,
If your towers have insulated guy wires, assuming you have yagi's on top for
"top loading" why not shunt feed one of the taller towers for 160? For the
winter, the radials can lay on the snow or ground, and can connect directly
to tower legs.
Articles appeared in Ham Radio by John True, W4OQ, later N4BA, and more
recently by Gary Breed, K9AY, on how to feed them. Also, the series
capacitor on the omega match can be adjusted to move up and down the band
with low SWR.
To your questions:
If you have a good ground, the bandwidth will not be as good as if you have
a poor ground system. One can typically get 60 - 70 KHz where the SWR is
under 2.0 with a good ground radial system.
For a 1/4 wave inverted L antenna, about 60 feet up and 67 feet out, the
antenna impedance with zero reactance will be in the range of Zant = 18 to
25 ohms.
A transformer or UnUn will match the inverted-L to 50 ohms, you need no
capacitor at the feed point. Amidon, ICE and others make them in both
assembled and kit forms to match 18ohms, 22ohms, etc. depending on the
windings used.
If you make the wire long enough to use a series capacitor, and it is only
60 feet vertical, you will have about a 3/8 wavelength inverted L, 60 feet
up and 125 feet out, and most of your radiation will be horizontally
polarized and straight up. The capacitor will need to be high voltage
rated, like a vacuum variable and will be about 250 pfd, as the impedance of
the antenna will be about
Zant = 50 + 400j ohms, and the capacitor adds - 400j ohms to tune out
reactance.
If you can make the vertical part of the wire 80 to 85 feet tall, then the
total length can be about 160 feet or 5/16 wavelength and 400 - 500 pfd of
series capacity at the feed point will match 50 ohms, as the antenna
impedance will be about
Zant = 50 + 200j ohms, so a larger capacitor will tune out the reactance.
Email me direct if you want more information.
Good luck and Happy 2004, George K8GG
----- Original Message -----
From: "Gregg Seidl" <k9kl@direcway.com>
To: <Topband@contesting.com>
Sent: Monday, January 05, 2004 11:20 AM
Subject: Topband: 160m int L
> Well the snow is finally starting to fly here in Wisconsin so it is time
to
> put up a 160 antenna.I have used an inteverted v here for years with the
> apex at 70 feet and the ends at maybe 30 feet,pretty poor.......I would
like
> to try an inverted L.It is my understanding that they need a cap. to tune
> them into the freq that you want.I have an 80,70 and 2 60 foot towers to
use
> as supports,and lots of room for radials.Are L's directional?What would be
a
> good starting point in length for say 1.85 mhz.Are they broadbanded?Any
> ideas???? Gregg K9KL
--- snip ---
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