Topband: 80/160?

[Guy Olinger K2AV]

Hi, Jim,

The problem in your proposal is that the location of the relay must be
the highest possible voltage on 80m. You need 20 kV maybe more at QRO.
There is a better way to get 80/160 off the same wire. The trap still
leaves you with a 1/4 wave vertical that takes no advantage of the
rest of the wire.

The better deal is to do all the work at the bottom and feed an
existing 160 1/4 wave inv L as an 80m end-fed halfwave L (EFHWL). The
80 EFHWL is probably the best all around 80 m single wire antenna. An
80 EFHWL will significantly outperform an 80 1/4 wave vertical.

80 EFHWL’s are not wildly popular because you can’t feed them directly
with 50 ohm coax and no one makes a commercial box for the base.

No one makes a commercial box for the base of an 80 EFHWL because the
80 EFHWL is not wildly popular.

You can do an 80/160 which makes use of an UNMODIFIED 160 inv L over
FCP.  Relay at center of FCP changes way FCP is fed when set for 80m.
No changes to aerial wire or FCP per se. All the tuning circuit for
dual banding is near the ground and circuit can accommodate multiple
SWR ranges/center freqs on 80/75.

This is discussed on k2av.com in the 80/160 Dual Band indexed section.

Tested this design in 14 hour 2016 CQWWDX CW effort at K2AV, official
SOSB(A)/80 score: 266 Q's 18 Zones 77 Countries, good enough for #2
North America (QTH in North Carolina, not New England) and a top
scores listing in the CQ magazine article. Also, in the 2017 ARRL SS
CW, worked 403 QSO's on 80 meters alone, one of only three stations in
the contest to work more than 400 QSO's on 80 meters.

An 80 EFHWL works very well and avoids altogether several loss factors
which bedevil 80m 1/4 wave verticals.

Rather than current maxima at the ground, the EFHWL has the advantage
of current maxima up at the bend, a significant reduced loss
advantage. The half V half H wire polarization puts out a
hemispherical pattern, which has no weakness at azimuth or elevation.
There's no doughnut hole at the upper takeoff angles, and still is
never less than the 1/4 wave at the low angles. This means you do not
have skip zones on 80 unless the band has gone way out.

It 's about time that the 80 EFHWL got some deserved good press.

73, Guy K2AV


On Wed, Apr 18, 2018 at 1:34 PM Jim Miller <jtmiller47 at gmail.com> wrote:
>
> Rather than use a trap at the top of an 80m vertical to transition to a 160
> inverted L has anyone tried a vacuum relay or even two in series at 1500w
> to handle the highvoltage when on 80m?
>
> Tnx
>
> Jim AB3CV
> _________________
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