[Antennas] Re: Elevated Ground Plane Question

2002年10月08日 10:19:56 -0400

At 04:01 AM 10/8/2002 -0400, you wrote:
>Hi All:
>> I have a 160 meter, 1/4 wavelength wire vertical that is feed 
> approximately 30 feet off the ground. The radials are horizonal from the 
> feed point and parallel to the ground. I have the opportunity to raise 
> the radials to a height that is almost as high as the top of the vertical 
> radiator [approximately 160+ feet] and am wondering if this will enhance 
> the antenna effectiveness or not. I am concerned about wave cancelling.
>> If anyone has a software program where this situation can be 
> simulated, I would be very interested in the results. I will try it out 
> in any case, but am interested in what modeling or experience 
> suggests. Please note the radials would now start at the feed point some 
> 30 feet off the ground with the other end being elevated to 160+ feet.
>> Thanks for taking the time to read this and to share your thoughts 
> with me.
>>Ron W7MRR
>
Ron,
I think you would likely be disappointed with the results if you were
to raise the far ends of the radial wires to the same level as the
top of the radiator. If I understand what you are proposing, the
radials would form an inverted cone with the point at the feed
location.
If you think of the radials as approximating a solid cone, what you
would be doing is essentially flaring out the braid of the coax that
feeds the antenna. The radiator would be an extension of the
center conductor, and the radials would be an extension of the
braid at an angle to the radiator. The RF current along the radials
flows in the opposite direction (with respect to the feedpoint) of the
current in the radiator, so the radiator and radials would "fight"
against one another in trying to create a radiating field. That is,
the waves radiated by each would tend to cancel.
If you have additional supports around the existing radiator, you
might be better off using them to support a ring (square?) of
phased vertical radiators. Of course, each vertical would need its
own set of radial wires.
73,
Dave NB4J
--
Dave Kelley, NB4J
Lewisburg, PA
Union County