[Lf] Measuring ERP]

[Andre' Kesteloot]

James Moritz wrote:

> Dear Laurie and Group,
>
> Laurie wrote:
> > Yes,but not all the power fed to an amateur antenna is radiated due to
> > trees buildings etc.So I suppose the only real test is to measure the
> > field strength and even this has its problems ,I belive(ground
> > conductivity etc.) 73s Laurie.
> >
>
> Since ERP, and antenna gain, is defined in terms of the field
> strength at a point distant from the antenna, it would seem that the
> only definitive way to measure ERP or gain is by field strength
> measurements. Since, as Laurie points out, the field strength
> depends on many environmental factors, the answer to the
> question 'what is the ERP' then becomes 'it depends where you
> are measuring it'.
>
> The licence regs have nothing to add on this matter; I suppose a
> sensible suggestion would be at a distance great enough so near-
> field effects are negligible, but near enough that ground losses are
> negligible - say several km. Experience shows that the results of
> doing this have quite large variations depending on the receiving
> site, so there is no easy answer to measuring ERP.
>
> Cheers, Jim Moritz
> 73 de M0BMU