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-----Messaggio Originale-----
Da: Mike Michon <michon@eatel.net>
A: <topband@contesting.com>
Data invio: martedì 14 dicembre 1999 16.54
Oggetto: Topband: Dipole/Reflector
>
> I wonder if anyone has seen any information on using a 160 meter dipole
with
> a reflector, ie 2 element wire beam for 160 meters.
At IR4T we have a wire but reversible yagi made with a dipole and an
electrically adjustable reflector/director at a spacing of .18 wavelenght.
The antenna is horizontal and suspended about 200 ft over a flat ground.
> If the thing is about
> 75 feet high, still very low for an effective horizontal antenna for low
> angle radiation on this band, does the reflector change the mostly
straight
> up radiation pattern.
At 75 feet an optimized yagi (your lenghts are wrong) over a flat ground has
the maximum radiation at an elevation of about 60° instead of the stright
90° of a simple dipole and shows some gain over the dipole from 10° to 70°
on vertical plane.
The beamwidth angle is about 80° wide at an elevation of 30°. (see the
attached Yag_d160.gif)
The F/B is not startling because the ground is close and stay in the area of
6-7 dB along a narrow bandwidth.
>
> We tried one for the 160 meter contest, but it was hard to say how it
worked
> as conditions were poor in MS. Plenty of Thunderstorms and crashing and
> banging.
>
> The antenna was physically east/west, lobes north south.
>
> We manged to work DF2PY before the contest, but no EU during the contest.
We
> had one Beverage to North, but conditions were very poor for hearing.
>
> The antenna semed to do well to California, which is off the end.
>
> I know on air tests are purely subjective, but we are still amateurs and
> don't have an antenna testing facility.
>
> Anybody have any ideas about how the pattern of this thing would be???
Look at the attached .GIF files that show the optimized yagi vertical
pattern compared to a dipole (Yag_160.gif), and yours (Yag_o161.gif)
that has much too long elements, again compared to the simple dipole.
If a good beverage can be erected for receiving purposes, a good vertical
antenna will outperform the 1/8 height yagi on a pure DX traffic.
>
> 266 feet dipole, centerfed ladder line at 75 feet, and a 300 foot
reflector
> a quarter wave away at 75 feet, basically parallel to the driven
element???
Centering the antenna at 1.840 and not counting the shortening due to the
end effects, using a wire diameter of .01, ft the optimal dipole lenght @75
feet height is 127.8 ft and the reflector 133.8 ft.
73,
Mauri I4JMY
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