[TowerTalk] Fw: Fw: Why radials improve radiation!

[Jim Lux]

On 5/23/11 9:45 AM, Al Williams wrote:
>
> ----- Original Message -----
> From: "Al Williams"<alwilliams at olywa.net>
> To: "WA8JXM"<wa8jxm at gmail.com>
> Sent: Monday, May 23, 2011 9:43 AM
> Subject: Re: [TowerTalk] Fw: Why radials improve radiation!
>
>
>> No, it doesn't help me understand because it just rephrases what I tried
>> to say in 2b of my question.
>>
>> In case of the dipole, if the two sides are of equal length then it would
>> seem there is a place for the charge and discharge to be identical.
>> However if the feedpoint is moved off-center the radiation according to
>> EZNEC remains the same. Where is the current to charge/discharge the
>> shorter side (to make up for the shorter wire) going?
>>




An interesting question.

The current distribution along the antenna is the same, regardless of 
the position of the feedpoint.  It's determined by the coupling of one 
part of the antenna to another (and the physical connections among the 
parts of the antenan). If you looked at the dipole, with NO feedpoint, 
sitting in a field that excited it, for instance, you'd see the same 
distribution (often represented as a sort of half sinusoid).

And, that antenna will radiate (with no feedpoint).  That's what radar 
cross section is all about: the resonant dipole both accepts and 
re-radiates power.


OK. the current in the two sides of the feed point must be identical 
(the feed is a two terminal device), so the amount charge being pushed 
into or out of the two sides is the same (although opposite in sign).

One way to look it is that there is a sort of "transformer" effect 
between the sides of the antenna.  Current flowing in the short leg is 
coupled to the long leg (by the magnetic field mostly).