Why is the optiamal element length 91% if half the wavelength for a dipole?

[RCA Dimensia]

"Actual best length of a dipole antenna is about 91% of that of 1/2 wave in free space, so to be precise about this, the lengths below are already reduced by approx. 9%."

TV Rabbit Ear

I meant OF the wavelength.

 

[KJ6HYC]

Assuming your statement is true. Perhaps the velosity of the wire?

 

[wavrider]

Assuming your statement is true. Perhaps the velosity of the wire?

1005/freq gives you wl in free space

468/freq gives half wl with velocity factor figured in sort of.

234/freq gives 1/4wl with velocity factor figured in sort of.

Will this formula hold up everywhere in every antenna build or installation?

The answer is a big NO, but it will get you in the ball park.

 

[Captain Kilowatt]

That site in the original post is the only one I have seen that states 9% shortening. Everything else I have ever seen or heard states about 5% which is what I believe to be true unless you are using a really fat conductor on VHF/UHF frequencies. The reason is partly due to the velocity factor of the element material and mostley due to something called "antenna end effect" which is a small capacitance that is formed by the antenna elements in air and has the effect of "detuning" the antenna. In order to compensate the antenna length must be changed slightly.

 

[pizzaman]

You answered your own question, "in free space". As you bring your dipole into relationship with the ground the charistics of that antenna change.

Bernie
W8NBC

 

[Kamikaze]

Optimal for what?

 

[Captain Kilowatt]

Optimal for what?

Proper tuning and operation.