Properties Of Hf Radiation; And Consequences For Measurements - Gigahertz Solutions HF59B Bedienungsanleitung

Properties of HF Radiation...

Across the specified frequency range (and beyond), HF radiation can
cause any of the following effects on the materials exposed to it:
1. Partial permeation
2. Partial reflection
3. Partial absorption.
You may, therefore, come across various extremely differing field dis-
tributions within one building, with strong peaks at individual spots
(so called "hotspots").
Minimum Distance
In order to measure the quantity of HF radiation in the common unit
"power density" (W/m²), a certain distance has to be kept from the
HF source. The distance depends on the frequency – the higher the
frequency the lower the distance. The transition frequency between
so called far field and near field conditions is not determined exactly,
but here are some typical distances:
27 MHz from approx. 27 meters
270 MHz from approx. 2.7 meters
2700 MHz from approx. 0.27 meters
That means the distances are inversely proportional to the frequen-
cies.
Polarization
When HF radiation is emitted, it is sent off with a "polarization". In
short, the electromagnetic waves propagate either vertically or hori-
zontally. Cellular phone technology, which is of greatest interest to
us, is usually vertically polarized, or at an angle below 45°. Due to
reflection effects and the many ways in which a cellular handset can
be held, we also observe other polarization patterns. Therefore, it is
always strongly recommended to measure both polarization planes,
which is defined by the orientation of the antenna.
... and Consequences for the Measure-
ments
When testing for HF exposure levels in an apartment, home or prop-
erty, it is always recommended to record individual measurements
on a data sheet. Later this will allow you to get a better idea of the
complete situation.
It is equally important to repeat measurements several times: First,
choose different daytimes and weekdays in order not to miss any of
the fluctuations, which sometimes can be quite substantial. Second,
once in a while, measurements should also be repeated over longer
periods of time, since a situation can literally change "overnight". Ma-
jor changes in exposure levels can, for instance, already be caused
by a transponder only being tilted down by a few degrees (e.g. during
installation or repair works on cellular phone transmitters). In particu-
lar, however, the worldwide extremely rapid expansion of the cellular
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