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March 13th 06, 08:16 AM posted to rec.radio.amateur.antenna

Owen Duffy

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Radiation Resistance

On Sun, 12 Mar 2006 20:56:05 -0600, (Richard
Harrison) wrote:

Roy, W7EL wrote:
"Do the proper substitutionn and you`ll get the correct answer."

Yes. The warning also appears on page 137:
"In developing the field expressions for the short dipole, which were
used in obtaining (5-56), (5-56) is the value of radiation resistance,
the restriction was made that lambda is much larger than the length of
the dipole L." No problem there, Reg specified a short monopole.

Kraus does a sample calculation for a short dipole. I used Kraus` data
and got the same answer when duplicating his calculation.

But Reg was not asking for an answer to a specific problem. Reg was
asking for the value of the constant in a formula of the same form.
Kraus gives it as 80 pi squared for a dipole.. This is 790.

We know that a monopole has half the resistance of a dipole. Example: 73
ohms and 36.5 ohms. 790 / 2 = 395. That`s not a resistance, it is only
the value of a constant which must be multiplied by (L/lambda) squared
to give the radiation resistance of a very short monopole.

Is all that to mean that you used the formula given by Kraus for a
short thin dipole and applied your own rule to halve the coefficient.

In your original response you said "395 It is found on page 137 of
Kraus` 1950 edition of "Antennas"."

Is that correct, or did you make the number 395 up according to your
own rules and then attribute it to Kraus?

Owen
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