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Digital High Frequency Analyser HF59B
sion of testing uncertainties to the specified
accuracy of the used HF analyzer due to the
narrowness of indoor spaces. According to
the "theory" quantitatively accurate HF
measurements are basically only reproduci-
ble 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 sys-
tem-immanent measurement uncertainties as
low as possible, it is imperative to carefully
follow the measurement instructions.
As mentioned earlier in the introduction, only
slight changes in the positioning of the HF
analyzer can lead to rather substantial fluc-
tuations in measurement values. (This effect
is even more prevalent in the ELF range.) It is
suggested that exposure assessments are
based on the maximum value within a lo-
cally defined area even though this particu-
lar 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 differ-
ent readings within 24 hours at exactly the
same spot. The maximum value across a
locally defined area, usually changes only if
the HF sources change, which is why the
latter value is much more representative of
the assessment of HF exposure.
© Gigahertz Solutions GmbH, 90579 Langenzenn, Germany
Step-by-Step-Instruction to
HF-Measurement
Preliminary Notes Concerning the An-
tenna
The supplied logarithmic-periodic antenna (or
aerial), has exceptional directionality. Thus
it becomes possible to reliably locate or "tar-
get" specific emission sources in order to
determine their contribution to the total HF
radiation level. To know exactly the direction
from where a given HF radiation source origi-
nates is a fundamental prerequisite for effec-
tive shielding. Our logarithmic periodic an-
tenna, the "LogPer antenna", provides a dis-
tinct division of the horizontal and vertical
polarization plane. Also the frequency re-
sponse is exceptional. There is a patent
pending for its design.
The missing directionality of standard tele-
scope antennae is one of the reasons why
they are not suited for reliable HF measure-
ments in building biology EMR.
Important:
As the LogPer Antenna provided with this
instrument is shielded against ground influ-
ences one should "aim" about 10 degrees
below the emitting source one wants to
measure. This is to avoid distortions of the
reading.
The upper edge of the foremost resonator is
a good "aiming aid" for the required angle. It
Revision 4.5 (December 2006)
does not matter if the angle gets a little too
wide.
The readings from the instrument's display
reflect the integral power density in the "an-
tenna lobe". (ie., the antenna is most sensi-
tive, with a rounded peak, to radiation from a
direction parallel to its axis with the sensitiv-
ity tapering off rapidly with increasing angle
of incidence.)
The frequency range of the LogPer aerial
supplied covers cellular phone frequencies
(e.g. GSM800, GSM1900, TDMA, CDMA,
AMPS, iDEN), 2.4-GHz (DECT) cordless
phones, frequencies of third generation tech-
nologies, such as UMTS, WLAN and Blue-
tooth, as well as other commercial frequency
bands and microwave ovens. All the fre-
quencies in between are also included. This
is the frequency range which you would find
most
pulse-modulated signals, concerned
scientists are worried about.
For monitoring of these critical sources of
radiation as conveniently as possible the fre-
quency band of the LogPer aerial supplied
together with the instrument has been lim-
ited intentionally by its design to frequencies
above 800 MHz, i.e. frequencies below 800
MHz are suppressed. This reduces the im-
pact of most sources like radio broadcasting,
television stations or amateur radio on the
measurements to an acceptable level. Yet
few very strong sources, e. g. FM broadcast
may still be picked up in some intensity. So
don't be surprised if your analyzer picks up a
local radio station!
In addition, there are numerous sources of
radiation in the lower HF band which are not
pulsed (i.e. amplitude modulated). By their
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