[The following is an edited and upgraded version of my direct email to
fellow PVRC'er Jim, AB3CV]
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
Hi, Jim,
The difficulty with your suggestion is that the relay location must
necessarily become a voltage node in breaking up the 160 wire. With
its absolute end to the active wire, it will carry the antenna's
highest resultant RF voltage. You need a 10 kV maybe even 20 kV rating
at QRO. And you still only have an 80 meter 1/4 wave being used out of
the 80m halfwave length of wire. Using the trap is still a 1/4 wave
vertical taking no advantage of the rest of the wire.
There is a better way to do 80/160 on the same wire: do all the tuning
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 single wire 80m antenna. The 80 EFHWL already has as one of
it's components a 1/4 wave vertical, but uses it more efficiently with
the RF current maximum at the top. Current max at the top better
clears local clutter, instead of a bottom max more heavily inducing
lossy ground.
The part vertical part horizontal wire puts out a hemispherical
pattern, which has no weakness at azimuth or elevation. The pattern
has 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 long.
80 EFHWL’s are not wildly popular because you can’t feed them directly
with 50 ohm coax and no one makes a QRO commercial box for the base of
the antenna.
No one makes a QRO commercial box for the base of an 80 EFHWL because
the 80 EFHWL is not wildly popular.
Catch 22.
You can do an 80/160 which makes use of an as-is 160 inv L over FCP.
Relay at center of FCP changes the way the FCP is fed on 80m. Again,
there are no changes to the 160 aerial wire and FCP per se. All the
tuning circuit for dual banding is near the ground and the circuit can
accommodate switched multiple SWR ranges/center freqs on 80/75.
This is discussed on k2av.com in the 80/160 Dual Band indexed section.
I stress and contest-tested this design in the 2016 CQWWDX CW and the
2017 CW SS.
In the 2016 CQWWDX CW single band effort at K2AV, official published
score: SOSB(A)/80 266 Q's 18 Zn 77 Cty. That was good enough for #1
4th call area (QTH: NC), #2 North America and a CQ Magazine top scores
listing. It was only 14 hours with a lot of multiplier-digging. See:
https://www.cqww.com/scorescw.htm?yr=2016 Set call to K2AV and hit
submit. Click on Cert symbol to verify rankings.
https://www.cqww.com/results/2016_cq_ww_dx_cw_results.pdf Search on K2AV.
In the 2017 ARRL SS CW, 403 of my QSO's were on 80 meters. Three
stations in the entire contest worked 400 or more QSO's on 80 meters.
See:
http://www.arrl.org/results-database?ss_class=&ss_sect=&clb_name=&ss_call=&sort0=ss_80+desc&sort1=&sort2=&event_id=91412
It 's about time the 80 EFHWL got some deserved good press.
An 80 EFHWL works very well and avoids altogether several loss factors
which bedevil 80m 1/4 wave verticals, particularly on small lots. The
K2AV 160L over FCP is decidedly ordinary, middle-sized, definitely NOT
exceptional, other than its use of an FCP, attention to Loss List
issues and end-feeding on 80 meters. Anyone with 50-60-70 foot trees
or equivalent antenna supports should be able to match K2AV's signal,
IF they pay attention to the issues and recommendations on k2av.com.
The combination design will put a small lot station on both 160 and 80
very effectively with the single aerial wire.
73, Guy K2AV
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