Made in Germany
22
© Gigahertz Solutions GmbH
… and Consequences for the Execu-
tion of Measurements
When testing for HF exposure levels in an apartment, home or
property, it is always recommended to
record individual meas-
urements
on a data sheet. Later this will allow you to get a better
idea of the complete situation.
It is 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”.
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 build-
ing and also potential HF sources inside the building (e.g. WLAN
access points, also from neighbours).
Furthermore, you should be aware that taking measurements in-
doors adds another dimension of testing uncertainties to the speci-
fied accuracy of the used HF analyser due to the narrowness of in-
door spaces. According to the “theory”, quantitatively accurate HF
measurements are basically only reproducible under so-called “free
field conditions”, yet we have to measure HF inside buildings be-
cause this is the place where we wish to know exposure levels. In
order to keep system-immanent measurement uncertainties as low
as possible, it is imperative to carefully follow the measurement in-
structions.
As mentioned earlier in the introduction, even slight changes in the
positioning of the HF analyser can already lead to rather substantial
fluctuations in measurement values. (This effect is even more preva-
lent here than in the ELF range).
It is suggested that exposure
assessments are based on the maximum value within a locally
defined area
even though this particular value might not exactly
coincide with a particular point of interest in, for example, the head
area of the bed.
The above suggestion is based on the fact that slightest changes
within the environment can cause rather major changes in the pow-
er density of a locally defined area. The person who performs the
HF testing, for example, affects the exact point of the maximum
value. It is quite possible to have two different readings within 24
hours at exactly the same spot. The maximum value across a locally
defined area, however, usually only changes if the HF sources are
subject to change. This is why the latter value is much more repre-
sentative for the assessment of HF exposure.
Preliminary Notes Concerning the Antenna
The supplied logarithmic-periodic antenna (or
aerial), has excep-
tional
directionality
. Thus it becomes possible to reliably locate or
“target” specific emission sources in order to determine their contri-
