Recent experiments with short beverages have proved interesting and
informative. Since all the positions and combinations possible on my little
piece of ground have been tried, I've had to quit before all my questions
were answered. Some of the following observations may be based on
incomplete data and as such are subject to debate.
Six beverages were constructed. All were 270 feet in length. One was 30
inches above ground and inside the TX antenna elevated radial circle. The
rest were laying on the surface of the earth or on top of the dead grass.
These were placed from inside the radial circle to as much as 60 feet
outside the circle (in my neighbors yard). Galvanized fence wire and #24
insulated copper wire were both used.
As was expected, interaction between the TX system and the beverages inside
the radial circle occurred. Unexpectedly, the amount of interaction was
nowhere near as great as computer modeling predicted. Useable results were
obtained from even the worst case placement.
As has been noted on this list in the past, placement near and PARALLEL to
a metal fence caused no noticeable degradation. However, fences near the
ends of the wire, and nearly PERPENDICULAR to it, caused quite a bit of
pattern distortion and loss of F/B. Modeling the fences did not show this
effect. There was only so much real estate to work with, so no more could
be done to explain this. This effect caused me a great deal of confusion
initially, because there was still a lot of degradation when the TX antenna
system was removed from the picture.
The 270 foot BOG (beverage on the ground) has a "gain" about the same as a
FLAG.
While my rotatable Flag has a real cardioid pattern (easily observed back
null about 30 dB), none of the beverages had a good null off the back in
spite of the model predictions. The F/S was better and the front lobe
seemed to be narrower than predicted in all cases. The 30 inch high wire
under the elevated radial system had a null off to one side. It was very
deep and I first mistook it to be a figure 8 pattern similar to what
appears in "Low Band DX'ing".
A/B switching between the Flag and the various wires produced a tie in
performance on 160. At times one would have a much better S/N, then other
times the reverse would be true. I'd like to believe that the beverages are
responding to lower angles better, but I have no way to prove that. On 80,
the BOG's are way better than the Flag and are even pretty good on 40
compared to my poorly phased 4-square.
My Flag has the advantage because I can turn it. It also suffers far less
from interaction with the other antenna systems on the property. The shorty
beverages are much simpler and cheaper to construct, but require a long
straight clear run of real estate to get the best out of them. However,
even when placed poorly, they are quite useable, if you can point them in
the right direction.
The "elevated" wire had a measured surge impedance of 450 ohms. The BOG's
were all 300 ohms +/- 10%. This is over my excellent ground; wet, highly
alkaline, old farm ground. (Of course, it's now all asphalt and concrete
outside the subdivision)
While not nearly as good as a longer version, these "shorty's" are
certainly worth putting up. I would go so far as to say that modeling these
wires close to the ground gives misleading results and you are better off
trying it to see if it works for you. You might be surprised.
73,
Larry - W7IUV
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