Dennis, that is a good question. As you say there are two ways that coaxial
cable shield current is induced. Directly when the shield forms the third
leg of a 'tripole' antenna, and when current is coupled by the antenna
field.
Given the feedline length, physical relationship to the dipole, and dipole
height, I can model this for you in NEC. Otherwise, I would not bother with
a balun. While there may be feedline radiation, it is still radiation.
Dave WX7G
On Thu, Jul 23, 2009 at 11:57 AM, Dennis Berry <dennisberry@worldnet.att.net
> wrote:
> I know this forum is for modeling, but with the talent of hams in this
> group, I'm hoping the question will be pertinent and allowed.
>
> I understand the benefits of baluns in say a dipole antenna fed with a coax
> antenna. My question is lets say you have an average lot where the feedline
> cannot go away from the antenna at a 90 degree angle, but instead must run
> somewhat parallel or say even at a 45 degree angle to the dipole. I would
> assume that a balun then looses it's effectiveness as one side of the shield
> is skewed by the radiation from the dipole side it is favoring? (assuming
> the balun is at the feedpoint)
>
> It would seem that currents on the feedline side would be induced onto the
> shield? I'm not wanting to start a debate, just trying to understand if a
> balun at the antenna center feed is still effective if you cannot run the
> coax at a 90 degree angle, and possibly quite to one side of the dipole leg.
>
> Looking for some wise advice on this issue, and thanks in advance.
>
> Dennis, NU8S
>
> Note: reason being I am thinking of hanging some type of 160/80M dipole
> over a bit of a ravine, and the feedline cannot run at a 90 degree to the
> dipole. If it is not worth putting a balun at the center, I'll not bother,
> so trying to understand if it will be helpful. It's a steep ravine and only
> one to cross it once, with my legs and age. hihi...
> _______________________________________________
> Antennaware mailing list
> Antennaware@contesting.com
> http://lists.contesting.com/mailman/listinfo/antennaware
>
_______________________________________________
Antennaware mailing list
Antennaware@contesting.com
http://lists.contesting.com/mailman/listinfo/antennaware
|