[Lf] Re. ERP]

[Andre' Kesteloot]

WarmSpgs at aol.com wrote:

> In a message dated 10/20/00 8:49:46 AM Eastern Daylight Time,
> j.r.moritz at herts.ac.uk writes:
>
> << 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. >>
>
> That is exactly right.  A proper determination of ERP by field strength is
> not a trivial matter, and cannot be done with just one or two measurement
> points.  In commercial practice, we run a survey using a number of points
> along each radial from the antenna system at which it is desired to measure
> the ERP.  Points which are suspect, either because of objects in the
> proximity of the field strength meter or because the readings there vary too
> far from the other points, are discarded.  Readings are converted back to the
> equivalent strength at 1km using the inverse proportion of the distance
> (assuming the distance is not so great that earth attenuation must be taken
> into account) and averaged.  As I say, this process is repeated for each
> radial at which it is desired to determine ERP.  Where a "maximum ERP" limit
> applies to one's emissions, it is necessary to check enough radials to ensure
> that the direction of maximum ERP is, in fact, being measured.
>
> Random spot measurements are sometimes worse than useless; especially when
> applied selectively, as has been the case so far with CFA antennas.
>
> 73,
> John