[TowerTalk] Omnidirectional antenna for domestic contests. Re: TowerTalk Digest, Vol 154, Issue 18

[Joe Subich, W4TV]

On 10/12/2015 10:50 PM, Jim Brown wrote:
> But at lower angles (30 degrees and below), which is where most of
> the stations we want to work in a domestic contest come in,

While that may be true for you on the left coast (the land of fruits
and flakes), it is most certainly untrue for those in W3, W4, W8, W9
and W0.  Most QSOs for those in flyover country are at takeoff angles
greater than 60 degrees on 80 and 40 meters.  However, that still
argues for a height of roughly 50 feet for an 80/40 trapped or fan
dipole (3/8 wave on 40 meters, 3/16 wave on 80 meters).  70 feet (60
to 80 feet) is to be avoided due to the overhead null on 40 meters.

73,

   ... Joe, W4TV


On 10/12/2015 10:50 PM, Jim Brown wrote:
> On Mon,10/12/2015 9:15 AM, Stephen Davis wrote:
>> I was indicating what my actual results are, regardless  of what
>> software indicates.   Also, if I had looked at software first, I might
>> still have done the NIVIS based on other practical experience noted by
>> others in the research I did.
>
> Nearly all published assessment of the vertical patterns of antennas has
> been on the basis of what is called take-off angle -- the vertical angle
> at which the antenna produces maximum radiation. That description leads
> to a VERY false result.
>
> In the tutorial I referenced, I looked at both high angle and low angle
> field strength (performance) as the height of horizontal dipoles was
> varied from 30 ft to 135 ft. I looked at 5 degrees, 10 degrees, 15
> degrees, and 70 degrees, picking data points off of a full vertical
> pattern. I looked most at 80, 40, and 20M.
>
> In general, the high angle field strength is greatest when it is about
> 1/4 wavelength high (65 ft on 80), and drops by only 1 dB if the height
> is increased to 3/8 wavelength (90 ft on 80M) or decreased to 1/8 wave
> (30 ft on 80). But at lower angles (30 degrees and below), which is
> where most of the stations we want to work in a domestic contest come
> in, the field strength increases by 4 dB between 1/8 wave and 1/4 wave
> high, and another 2 dB going to 3/8 wave. High angle field strength does
> not begin to drop much until you get higher than 3/8 wave.
>
> SO, repeating my statement, a low antenna does NOT work better for NVIS
> than a high one, and a high one works MUCH better beyond a few hundred
> miles. All of this is shown in easy to understand graphs in
>
> http://k9yc.com/VertOrHorizontal-Slides.pdf
>
> 73, Jim K9YC
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