Consequences For Measurements - Gigahertz Solutions HFW59D Manual

M a d e in G e r m a n y
... and Consequences for the Execution
of Measurements
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 important to repeat measurements several times: First, choose
different daytimes and weekdays in order not to miss any of the fluc-
tuations, 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 building and also
potential HF sources inside the building (e.g. WLAN access points,
also from neighbours).
Furthermore, you should be aware that taking measurements indoors
adds another dimension of testing uncertainties to the specified accu-
racy of the used HF analyser due to the narrowness of indoor 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 because this is the place
where we wish to know exposure levels. In order to keep system-im-
manent measurement uncertainties as low as possible, it is imperative
to carefully follow the measurement instructions.
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 as-
sessments are based on the maximum value within a locally de-
fined 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 power
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 ex-
actly 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 representative for
the assessment of HF exposure.
Preliminary Notes Concerning the Antenna
The supplied logarithmic-periodic antenna (or aerial), has exceptional
directionality. Thus, it becomes possible to reliably locate or "target"
specific emission sources in order to determine their contribution to
the total HF radiation level. Knowing the exact direction from where a
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