Topband: Make 80m vertical work on 160

[Guy Olinger K2AV]

>
>  "Franki ON5ZO" <on5zo at telenet.be> wrote:
> > Gentlemen, please your advice.
> >
> > If I were to convert my working resonant 80m vertical
> >into a 80/160m
> > antenna, I assume I have two basic options according to
> >the literature:
>

There are many options. They are reduced by embraced assumptions or a
requirement of only direct 50 ohm coax feed.

If one makes the concession that there may be a miscellaneous Z to match on
either or both bands, and is willing to construct a matching device, quite a
number of possibilities emerge.  While many have the space and mechanical
circumstances to erect one of several textbook antennas in current favor,
IMHO most folks have constraining mechanical circumstances that prevent any
easy use of the currently favored designs.

I saw one installation that had a 80m vertical wire which was supported by
an insulator well off-center on a rope between two decently tall  trees.
The feed point directly below was dictated by an out-building and the wire
rose nearly straight up. The radial mix was necessarily eclectic
and shortish, dictated by fences, house, patio, alley way, etc. The problem
was to add 160 to the only possible low band wire with any height on the
property.

My suggestion was to convert the portions of the rope clear of the trees to
wire. One side being well longer than the other, it was not "pure" and
(gasp) would have some degree of horizontal polarized radiation. It also
would present non-standard feed Z's on both bands and require matching.

Once the commitment was made to match whatever impedance presented at the
base on 160 and 80 and switch matching devices, the remaining problem was to
measure the eclectic Z on both band and build a match. The necessary
match components were read off the menu of a K2, having satisfactorily
matched both Z's with its auto-tuner. A pair of iron-powder toroids wound to
value, a pair of transmitting caps, and a couple of relays in a weatherproof
box did it.

The presentation of match components after autotune can now be done with a
K3 as well.

A miscellaneous wire solution that is actually possible at a given site can
be modeled in advance to avoid extreme Z's for match, and if series ground
loss can be minimized, results will be good.  A good design on 160 consists
of two considerations with everything else in 12th or 13th place: the least
resistive ground/counterpoise possible and enough effective length to raise
the feed point impedance to minimize whatever practically unavoidable loss
remains in the ground/counterpoise system.

The end result was that he had a passable (R component of feed Z greater
than series ground resistance) 160 antenna that got him on top band, without
being severely narrow, an 80 meter antenna that clearly worked for DX *and*
USA, and was less visible than before.

Purity of design is highly over-rated on 80 and 160 and does not trump being
on both bands.

Stations on the receiving end cannot tell that an antenna is or is not all
vertical.  Miscellaneous polarization doesn't show up pink rather than green
on anyone's receiver.

73, Guy.