As has been already stated, an 80M dipole makes a GREAT
WARC Band Antenna if it is reasonably flat (horizontal).
It is nearly 3/2 wavelengths (WL) on 30M, almost exactly
5/2 WL on 17M and almost exactly 7/2 WL on 12M resulting
in 6 lobes on 30M, 10 lobes on 17M, and 14 lobes on 12M.
The main lobes will be approximately 30 degrees from the wire
with secondary lobes spread out between them and somewhat
lower in amplitude. Basically, an 80M HORIZONTAL dipole
acts as a current fed Long Wire on the odd harmonics which
include all three WARC bands. The feed impedance is in the
range of 100 to 120 Ohms at harmonic resonance resulting in
less than a 2:1 SWR when fed with 75 ohm cable. On 30M
the SWR is closer to 3:1 since it is slightly lower than the
third harmonic. I recommend tuning the 80M dipole to 3.6 MHz.
FWIW, I have worked over 300 countries on each of the WARC
bands using a pair of 80M dipoles and a pair of 20M dipoles fed
with ladder line which produce a figure 8 pattern on ALL bands
from 10 through 30 Meters. If you place such a 20M dipole
in the same direction as the 80M dipole, it will fill in the holes
in the pattern of the 80M dipole, giving world wide coverage
with only 2 fixed dipoles.
ENJOY !
de Tom N4KG
On Sat, 11 Sep 1999 19:51:49 -0700 Paul Baldock
<paul.baldock@checksum.com> writes:
>
> I'd like to put up an 80M dipole trapped for 30M. Anybody have any
> design
> info?
>
> Paul
>
>
>
> Paul Baldock,
> CheckSum Inc.,
> PO Box 3279,
> Arlington, WA 98223.
>
> Phone (360) 435 5510
> Fax (360) 435 5535
> EMAIL paul.baldock@checksum.com
> WEB http://www.checksum.com
>
>
>
> --
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