[TowerTalk] Radiation angle

[K4SAV]

The two largest factors affecting the take-off angle of a horizontal 
dipole are the height above ground and the terrain surrounding your 
antenna. NEC based and similar programs will give you information on 
antenna efficiency and take-off angle over flat ground but they won't 
handle the terrain question. The only program I know of that handles the 
terrain is HFTA, but there may be others that I don't know about.  If 
you live in rugged terrain, or have sloping ground close by, it is 
possible that this can have a larger effect than the height directly 
under the antenna. 

An antenna on high ground with the ground sloping away from the antenna 
is a big advantage for developing a low take-off angle.  The most 
unpredictable ground is the really rough terrain that has lots of hills 
and valleys repeated, as you move away from the antenna. Sometimes this 
can be good, and often it can be bad depending on the operating 
frequency and antenna height, and of course this varies a lot with the 
azmuith angle.

Jerry, K4SAV

Jim Lux wrote:

>At 03:44 PM 12/8/2005, AD5VJ  Bob wrote:
>  
>
>>Does anyone know all the factors that affect the angle of
>>radiation from a horizontal dipole.
>>
>>Height being one of course, but are there others that
>>raise or lower the angle and /or broaden or narrow the
>>pattern.
>>
>>Has anyone ever really done a study on this?
>>    
>>
>
>
>Not to be glib, but the answer is yes, hundreds and hundreds of people have 
>studied this. Such studies, from both a theoretical and experimental 
>standpoint, form the basis for such useful programs as NEC.
>
>Now that computers are fast enough, it's really interesting to put a simple 
>horizontal dipole model into a decent code that renders the pattern, and 
>try changing things, like the lengths of the wires, the position of the 
>feedline, whether it droops, putting in other things near it. Modeling a 
>dipole over real ground takes a few seconds on a moderately fast Pentium A 
>couple or three hours of fooling around can be quite interesting.
>
>  I just ran a single dipole using NEC4 (using the 4NEC2 front end) over 
>Sommerfield Norton ground, and it took 2 seconds all told to run the model 
>and display the 3D pattern on a 3.6 GHz Pentium.
>
>A modeling program makes it easy to systematically change something to get 
>a good intuitive feel for what will happen.  As you move the dipole up, you 
>can see the lobes changing.  Actually, now that it comes up, I wonder how 
>hard it would be to render an animation of something like this.
>
>
>  
>