[Lf] EMRP, heff, Rrad]

[Andre' Kesteloot]

"Soegiono, Gamal" wrote:

> Dear LF friends
>
> A reliable way to calculate "effective height", "Rrad"
> and "EMRP" of relatively small vertical antennas.
>
> Depending on particular vertical antenna design, current
> profile along the antenna conductor may exhibit different
> shapes. The usually unknown current profile may be re-arranged
> to become a uniform (i.e. constant) current profile.
>
> The real antenna (arbitrary construction) produces a FS at
> a distance "d" from the antenna, while the current at its
> feed point is "I".
>
> Assume a new vertical antenna, in place of the rela antenna,
> having the same current "I" at its feedpoint and anywhere
> else along its conductor. Adjust the value for "height" in
> such, that the FS at the same distance "d" is the same as
> with previous real antenna. Now the value "height" constitutes
> what is referred to as "effective height".
>
> Make FS measurements at a multiple of distances and in
> a multiple of compass directions. Determine the distance
> "d" from antenna base to the measuring point in meters.
> Measure the magnetic fieldstrength "H" in Ampere per meter.
> Measure the antenna current "I" at its feedpoint in Amperes.
>
> For every measuring point, find effective height "heff"
> by solving the equation:
>
> heff = (H/I)*(lambda * d) / [1+(lambda/(2*pi*d))^2]
>
> Calculate the average of heff obtained for every
> measuring point.
>
> Calculate Radiation resistance "Rrad" from "heff":
>
> Rrad = 160 [Ohms] * (heff/lambda)^2
>
> Calculate the power radiated by a vertical monopole,
> using "Rrad" and "I":
>
> EMRP = Rrad * I^2
>
> 73 de Gamal