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HF38B
–
„Range“: When switching from ‘Coarse’ to ‚Medium’ for very small readings, it
could happen, that the instrument tolerance of +/- 6 dB full range is absorbed. In this worst
case there may be a factor 4 between the displayed numbers in ‚Coarse’ and ‚Medium’.
Example
: In ‘Medium’ you read 150
.0
µ
W/m². If worst comes to worst ‘Coarse’ might show between 0
.6 und 0.03 µW/m²
(instead of 0.15 µW/m² which would be the correct value). However, normally the
differences shown will be much smaller.
For comparing measurements (e.g. ‘before’ and
‘after’) take the same range
setting.
Evaluating the different radio services
The displays of the meters of this series show the sum of the total power density within
the frequency range of the most common digital radio services. This means for the often
dominating sources of DECT and GSM as well as analogue sources: Simply take the
readings and compare them to the building biology standard values!
To be able to evaluate the different radio standards and transmission and modulation
patterns with one single measurement technology, the following approach to compensate
for these differences is recommended:
UMTS/3G, LTE/4G, WiMAX, DVB, WLAN during full data transmission: The
modulation of these high-speed services includes high, needle-like peaks compared
to the average power transmitted. Such signals are referred to as
“high
crest
factor”
signals. Measure for 1 or 2 minutes by slightly panning the meter pointing to the
direction of the main source, and multiply the highest value by ten for a comparison
with the building biology recommendations6. Often you will find different
telecommunication services being present at the same time. With the help of the
audio analysis7, you will be able to estimate how much of the total value shown is
caused by such high crest factor signals. Depending on the proportion to the total
signal, please apply the following
“rules
of
thumb”:
Low portion of
“high
crest factor
signals”
audible: multiply display reading by 2.
~“Fifty
-
fifty”
-ratio: multiply display reading by 5
Dominating
“high
crest factor
signals”: multiply
display reading by 10.
Taking into account the multiple external factors of measurement uncertainty, this
approach is perfectly adequate for an assessment of the total pollution. The use of a
frequency filter and service specific correction factors will allow an increased accuracy.
It is generally accepted to use the highest reading in the room for
comparison with limit or recommended values.
