[TowerTalk] Takeoff angles HF VS VHF / F2 VS Es DE K0FF

[Tom Rauch]

> Lets talk apples to apples and oranges to oranges or the newbies will get
> totally confused. On F2 skip, which is the predominate mode on HF a low
> angle is almost always better than a high angle for long distance
> communication. I can demonstrate this clearly in my own shack on 20M any
> time with the 2 different 20M beams.

I agree with that. My 150 foot high 5 element 20 meter antenna 
was a real smoker into Europe and even the Caribbean from Ohio. 
The only time a lower antenna was better was when the band was 
really stretched out and I wanted to work in close.   

The same thing applies on 160 meters, except at even closer 
distances. My ground mounted verticals clearly beat my horizontal 
antennas even though some are 300 feet in the air!

They are about equal at distances from 100 miles to maybe two 
hundred miles, but beyond that the vertical is better a large 
percentage of the time. The wave angle is clearly very low even on 
160 meters and even at reasonably short distances.

The exception is at or just after sunrise during days when the band 
has a strong sunrise peak, or during geomagnetic storms.

> Another closely related hobby TV DXing using a similar approach. The
> antennas are purposely mounted low
> (15 feet), and turned vertical. This block most of the "groundwave" or
> Tropo signals because of the cross polarity ( On skywave, Faraday rotation
> pretty much does away with the original polarity). Then the antenna is
> tilted up by 10 degrees to enhance it's performance to the incoming wave.
> AGAIN this is Es and not F.

Tilting the antenna can't possibly have much effect unless the 
antenna is very directive in the elevation plane. Look at the ***free-
space pattern**** of the antenna, and the vertical plane HPBW. 
Only when the tilt is enough degrees to appreciably change the 
energy down at the angle to earth or up at the sky at the desired 
angle will tilting have an effect.

Tilting a large collinear vertical has an affect, if vertical pattern is 
narrow enough. Tilting an antenna with a wide freespace vertical 
antenna moves the straight up null to an angle more in the direction 
of top tilt but does little else to pattern.

While the idea of using a vertical is technically sound, unless they 
have a 40 foot long collinear vertical the 10 degree tilt is 
meaningless.


73, Tom W8JI
w8ji@contesting.com

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