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Digital High Frequency Analyser HF59B
Introduction to Properties and
Measurement of HF Radiation
This instruction manual focuses on those
properties that are particularly relevant for
measurements in residential settings.
Across the specified frequency range (and
beyond), HF radiation causes the following
effects in materials exposed to it:
1. Partial Permeation
2. Partial Reflection
3. Partial Absorption.
The proportions of the various effects de-
pend, in particular, on the exposed material,
its thickness and the frequency of the HF
radiation. Wood, drywall, roofs and windows,
for example, are usually rather transparent
spots in a house.
Minimum Distance
In order to measure the quantity of HF radia-
tion 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 fre-
quency between so called far field and near
field conditions is not determined exactly, but
here are some typical distances:
At 27 MHz from ca. 27 meters
At 270 MHz from ca. 2.7 meters
At 2700 MHz from ca. 0.27 meters
That means the distances are inversely pro-
portional to the frequencies.
© Gigahertz Solutions GmbH, 90579 Langenzenn, Germany
Polarization
When HF radiation is emitted, it is sent off
with a "polarization". In short, the electro-
magnetic waves propagate either vertically or
horizontally.
Cellular
phone
which is of greatest interest to us, is usually
vertically polarized. In urban areas, however,
it sometimes is already so highly deflected
that it runs almost horizontally or at a 45-
degree angle. Due to reflection effects and
the many ways in which a cellular handset
can be held, we also observe other polariza-
tion patterns. Therefore it is always strongly
recommended to measure both polarization
planes, which is defined by the orientation of
the antenna.
Please note that the LogPer-antenna sup-
plied with this instrument is optimized for one
polarization only (vertical if mounted to the
instrument - even if the horizontal "wing"
suggests the opposite.)
Fluctuations with Regards to Space and
Time
Amplification or cancellation effects can oc-
cur in certain spots, especially within houses.
This is due to reflection and is dependent on
the frequencies involved. Most transmitters
or cellular handsets emit different amounts of
energy during a given day or over longer pe-
riods of time, because reception conditions
and network usage change constantly.
All the above-mentioned factors affect the
measurement technology and especially the
procedure for testing. This is why in most
cases several testing sessions are necessary.
Revision 4.5 (December 2006)
Measuring HF Radiation
When testing for HF exposure levels in an
apartment, home or property, it is always
technology,
recommended to record individual meas-
urements on a data sheet. Later this will al-
low you to get a better idea of the complete
situation.
It is important to repeat measurements sev-
eral 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, meas-
urements should also be repeated over
longer periods of time, since a situation can
literally change "overnight." A transponder
only needs to be tilted down by a few de-
grees in order to cause major changes in
exposure levels (e.g. during installation or
repair of cellular phone transmitters). Most of
all it is the enormous speed with which the
cellular phone network expands every day
that causes changes in exposure levels. In
the future we will also have to deal with third
generation networks (e.g. UMTS/3G), which
are expected to increase exposure levels
considerably since their system design re-
quires much more tightly woven "cells" of
base stations compared to current GSM net-
works.
Even if you only intend to test indoors, it is
recommended first to take measurements in
each direction outside of the building. This
will give you an initial awareness of the "HF
tightness" of the building and also potential
HF sources inside the building (e.g. 2.4 GHz
telephones, also from neighbours).
Furthermore you should be aware that taking
measurements indoors adds another dimen-
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