On Dec 26, 2005, at 8:30 PM, Peter Dougherty (W2IRT) wrote:
> Concerning the multi-band dipole I put up the other day (the one with
> the QRM issues), after playing around for a couple of nights with
> this antenna, I'm noticing the performance on 160 is non-existent for
> anything more than about 600 miles away..... Granted, it's an
> electrically-shortened antenna with a lower capture area than a
> full-sized antenna, but I was expecting better than this, for sure!
The important question is - how high is it?
> I can not achieve a flat SWR at all, anywhere; it comes down to 2:1
> at 1830. It's in a Vee configuration with the apex at 68 feet, a
> fairly steep angle off the tower and the ends are around 15 feet off
> the ground.
68 feet is not very high with respect to 160m. Consider that a half
wavelength is 270 feet. 68 feet is barely 1/8 wave high. At that
height, and with the inverted V configuration, the main lobe of the
antenna is going straight up.
> I'm not expecting miracles off this antenna, but I'd at
> least like to have a shot into the Caribbean and Europe.
You need a vertically-polarized antenna. A lot will depend on what
sort of supports you have available. An inverted-L will work hung in
a tree with lots of radials on the ground. You could also suspend one
from your tower.
Or, you could do like me and shunt-feed your tower against a good
radial system. I have 25 60 foot radials down and a 15m high tower
with a modest tribander on top. I have a matching network for 80m and
160m. The shunt works well on both bands. Antenna is nearly a 1/4
wave on 80m, closer to 1/10 wave on 160m.
Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@arrl.net
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|