> A half wave vertical or a vertical dipole doesn't work well when
> elevated above ground because of reflection losses due to the
> Brewster angle.
Verticals in general (ground plane or vertical dipoles) are inferior
to a dipole more than 0.4 wavelength above ground unless they are
over a large expanse of salt water - e.g., "verticals on the beach")
because the horizontal antenna gets the benefit of approximately
6dB of "ground reflection gain". At 3/8 wave above "real" soil the
dipole radiation is better than that of the vertical from about 15
degrees up and the vertical is only marginally (2 dB) below 15 degrees
with very good soil (with even average soil the vertical is no better
than the dipole even at low angles).
Note - any NEC based modeling program will overstate the vertical
gain at low angles even with a "high accuracy" ground model.
73,
... Joe, W4TV
On 4/25/2011 1:21 AM, Richard (Rick) Karlquist wrote:
> A half wave vertical or a vertical dipole doesn't work well when
> elevated above ground because of reflection losses due to the
> Brewster angle. This problem is independent of any problems
> with feeding it. NEC may or may not model it correctly.
>
> Rick N6RK
>
> On 4/24/2011 7:52 PM, Jim Brown wrote:
>> On 4/24/2011 4:21 PM, Rick Karlquist wrote:
>>> It is difficult to feed a vertical dipole in the traditional
>>> way in the center without the feedline affecting the pattern.
>>
>> Rudy Severns, N6LF, figured out a way to end feed it, and I expanded on
>> it. I built my version and hung it from a pulley high in a redwood,
>> with the top about 110 ft above ground. It works, but when I compared it
>> to my horizontal dipoles, the dipoles were ALWAYS a couple of S-units
>> stronger. Before I built it and hung it in the tree I also modeled it in
>> NEC.
>>
>> See my power point on Coax Chokes for photos and details of my feeding
>> method and printouts of the modeling results. On the air comparisons
>> correlate quite well with the model predictions.
>>
>> 73, Jim K9YC
>> _______________________________________________
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>>
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