I'd give it a try, Rick! I think that you are likely to be surprised and
pleased with the results! Yagis ( or 1/2 Yagis) just want to work and are
very forgiving of offset elements!
I've built 2 and 3 element 40 meter yagis in the past that were wonderful
performers - especially on the morning and evening long paths. I've also
added directors and reflectors around my parallel 40/30 meter vertical
dipoles with really good results. (Just wires hanging in trees supported by
fishing line! They worked well!)
I also built an 80m 5-element steerable array for 80m (driver and 4
parasites that coul be remotely switched between reflector and director
tuning with relays and stubs). That one was a FEARSOME, "killer" DX
antenna! One of my proudest accomplishments! The driver and parasites were
1/4 wave verticals operated against elevated resonant radials - 4 for the
driver and 2 each for the four parasites)
You could put up an 80m inverted L for 80m, tuned as a director, and
parallel it with a 40m 1/4 wave director and operate it against elevated
resonant radials for 80 and 40m. You might need to play with it a bit in
EZNEC to "jiggle" the element lengths for best performance.
If you really want to "gild the lily", you can insert sorted stubs near the
feed-point of the vertical parasites to tune the parasite as reflectors, and
short the stubs with relays at the antenna elements to change to director
tuning to make the 1/2 yagi reversible! - That's how I implemented the 80m
steerable array - and it worked wonderfully well!! The array was steered
with a switch box in the shack to control the relays.
The deceptive thing about modeling vertical parasitic arrays, is that,
because of the vertical polarization and the absence of "ground-reflection"
additive gain, the gains that you will see in EZNEC are not so impressive
compared with horizontal yagis. However, the on-the-air performance can be
really impressive - especially on long-haul paths because of the low takeoff
angle.
I don't think that you are likely to accomplish much on 160 if you are
limited to 10.5 m.
Good luck! Have fun!! ( I really like modeling, building andplaying with
high erformance antennas! :) )
73,
Charlie, K4OTV
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Rick
Kiessig
Sent: Tuesday, November 05, 2013 9:45 PM
To: 'topband'
Subject: Topband: Vertical 2-element array?
I have a quarter-wave vertical for 40m on a steeply sloped lot, at about
100m AGL, 300m horizontally from the ocean. It currently has a relatively
poor radial field (more are in the works, of course); I use it entirely as a
multiband receive antenna, not for TX. A second fan-vertical element is
connected to the same feedpoint, configured as an inverted-L for 80m, which
I do use for TX, but rarely. It's resonant on both 40 and 80, and works on
160 at low power with an in-shack tuner.
Downhill, toward the ocean, is also the direction to EU and JA. On sloped
land like this, is a second vertical director-like element downhill, below
the first one likely to work (it would have to be limited to 10.5m height
above ground)? If so, would it buy me much? EZNEC suggests a slight
improvement is possible, but modelling this kind of system has been
problematic for me in the past, so I'm not confident of the results.
Are there other alternatives I should consider for increased gain on 40, 80
and/or 160? The horizontal space I have available above ground is very
limited, so things like an FCP or a K9AY loop are too big. I could make room
for a BOG or Beverage, but the longest run would be about 50m, and it's not
really in the right direction.
73, Rick ZL2HAM / ZM1G
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Topband Reflector
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Topband Reflector
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