Evaluation of EMF Exposure from Digital Terrestrial Television Transmitters

Abstract

This study presents results of a preliminary survey of the RF electromagnetic fields (EMFs) originating from digital terrestrial television transmitters. In situ-measurements of DVB-T2 signals were conducted in the city of Iasi, Romania, and its rural vicinity, where a 180 meters tall guyed mast for FM-/TV-broadcasting is installed. The measured E-field levels were found to be well below the exposure limits recommended by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) for the general public.

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21st IMEKO TC4 International Symposium and
19th International Workshop on ADC Modelling and Testing
Understanding the World through Electrical and Electronic Measurement
Budapest, Hungary, September 7-9, 2016
Evaluation of EMF Exposure from Digital
Terrestrial Television Transmitters
Eduard Lunca1, Alexandru Salceanu2, Silviu Ursache2, Mirela-Adelaida Anghel3
1Faculty of Electrical Engineering, 21 Prof. Dimitrie Mangeron Street, 700050 Iasi, Romania,
elunca@tuiasi.ro, +40 232 278683/1246
2Faculty of Electrical Engineering, 21 Prof. Dimitrie Mangeron Street, 700050 Iasi, Romania,
asalcean@tuiasi.ro, silviu_ursache@tuiasi.ro, +40 232 278683/1157
3Romanian Bureau of Legal Metrology, Bucharest, Vitan Barzesti Road nr.11, Romania,
mirela.a.anghel@gmail.com, +40213320954
Abstract – This study presents results of a preliminary
survey of the RF electromagnetic fields (EMFs)
originating from digital terrestrial television
transmitters. In situ-measurements of DVB-T2 signals
were conducted in the city of Iasi, Romania, and its
rural vicinity, where a 180 meters tall guyed mast for
FM-/TV-broadcasting is installed. The measured E-
field levels were found to be well below the exposure
limits recommended by the International Commission
on Non-Ionizing Radiation Protection (ICNIRP) for
the general public.
Keywords – EMF exposure, DVB-T2 transmitter
antennas, in-situ measurements
I. INTRODUCTION
The transition from analogue to digital terrestrial
television (DTT or DTTV) is a process in various stages
of implementation around the world [1]. In the European
Union (EU), DTT represents the most widespread
platform for TV reception, reaching over 100 Million
households – 250 million viewers [2].
DVB-T (Digital Video Broadcasting – Terrestrial) is
the DVB European-based consortium standard for the
broadcast transmission of digital terrestrial television. It
transmits compressed digital audio, digital video and
other data in an MPEG transport stream, using the coded
orthogonal frequency-division multiplexing modulation
(COFDM). DVB-T was first published in 1997 and first
broadcast in 1998, in the UK [3].
Although Romania started DVB-T broadcasting in
2005, it was only experimental. In 2012, the Romanian
authorities decided that DVB-T2 (Digital Video
Broadcasting – Second Generation Terrestrial) will be
the standard used for terrestrial broadcasts, as it allows a
larger number of programs to be broadcast on the same
multiplex (MUX). On 17 June 2015, the analogue
terrestrial television was switched off, with the exception
of the main public TV program (TVR1), which will
continue to be broadcast strictly in the VHF band until
the end of 2016 [4].
At the end of 2015, free-to-air DVB-T2 broadcasts on
MUX1, provided by the state-owned Radiocom, were
available for about 56% of the population [5]. In such a
context, we initiated a measurement campaign of the RF
electromagnetic fields originating from DVB-T2
transmitter antennas, first in the city of Iasi and its rural
vicinity. To our knowledge, no study has tried to evaluate
the in-situ DVB-T2 exposure in our country.
II. RELATED RESULTS IN THE LITERATURE
A number of studies concerning – at least partially –
the RF exposure from DVB-T systems were published
over the past decade, with the migration to DTT in the
European countries.
In Germany, extensive exposure measurements were
performed at more than 300 points in two DVB-T
starting-areas, Munich and Nuremberg. At 200 locations
in residential areas, measurements before and after the
switchover were carried out to determine a possible
change of exposure situation. Additional measurements
along defined lines and inside buildings were also
performed [6, 7].
In Belgium, The Netherlands and Sweden,
measurements of DVB-T signals were carried out in the
framework of a common survey of the RF
electromagnetic fields from emerging wireless
communication technologies. According to this study [8],
which was published in 2012, the exposure ratios from
DVB-T (if present) were the highest except GSM.
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A study from 2013, [9], deals with the
electromagnetic field exposure from a DVB-T transmitter
in the urban environment of Zagreb. Measurements of
electric field were performed at several key locations and
compared to theoretical calculations of the present field.
There are also several studies and reports concerning
the evaluation of the RF exposure from DVB-T, e.g. [10],
but all of these show that the RF exposure levels are
generally well below the exposure limits recommended
by ICNIRP [11]. This is also true in our case.
III. MEASUREMENT METHOD
Like its predecessor, DVB-T2 uses the OFDM
modulation scheme [12], which divides the available
bandwidth into a large number of closely spaced
subcarriers and transmits data in parallel streams. The
signal bandwidth can be either 8 MHz (in the UHF band)
or 7 MHz (in the VHF band). Currently, the DVB-T2
transmissions occur in the UHF band, relayed from a
number of transmitters located at high sites around the
country.
In order to measure such emissions, we adopted a
frequency-selective method based on a SPECTRAN HF-
60105 V4 spectrum analyzer (1 MHz – 9.4 GHz) in
conjunction with a calibrated BicoLOG 20300 antenna
(20 MHz – 3 GHz), both from Aaronia AG (Fig. 1). After
extensive investigations, taking into account the
characteristics of the DVB-T2 signals with respect to the
performances of the spectrum analyzer, the following
settings were established for assessing the DVB-T2
exposure: RMS (Root Mean Square) detector, resolution
bandwidth RBW = 5 MHz, video bandwidth VBW = 50
MHz (FULL), sample time SpTime = 250 ms (sweep time
ST about 750 ms, as reported by the MCS Spectrum
Analyzer Software), frequency span of 20 MHz, with the
center frequency (CF) of the spectrum analyzer equal to
the CF of the DVB-T2 signal.
Fig. 1. Instrumentation used for the survey
At each selected location, MAX HOLD
measurements were taken with the antenna oriented in
three orthogonal directions, at a distance of 1.5 m above
the ground or floor, for a sufficiently long time to allow
the trace to stabilize. During the investigations, a
minimum distance of 0.5 m was maintained between any
object and the antenna [13, 14].
All readings indicated by the spectrum analyzer
(power in units of dBm) were recorded and converted to
E-field strength levels, in units of V/m, by taking into
account the antenna factor and power losses in the
connecting coaxial cable [15, 16]. Then, the total E-field
at each location was calculated with the formula [17]:
222
zyxtot EEEE ++= , (1)
where Ex, Ey and Ez represent the three orthogonal
readings.
The specified accuracy of the HF-60105 V4 spectrum
analyzer is ±1 dB (typically), but higher deviations are
possible especially when approaching the so-called noise
floor or the maximum sensitivity of the instrument [18].
IV. RESULTS AND DISCUSSION
DVB-T2 exposure measurements were performed at
80 locations: 62 – in different areas of the Iasi city, 18 –
in the surrounding of the “Pietraria” transmitter, a 180
meters tall guyed mast for FM-/TV-broadcasting at
Pietraria, a village near Iasi. Fig. 1 shows the position of
the transmitter and considered measurements locations on
the map. Most of the measurements were taken outdoor,
in the period March 2016 – April 2016.
An overview of the VHF and UHF frequency bands at
a measurement location is shown in Fig. 3. At the
moment, only a DVB-T2 signal is present in the UHF
band, on channel 25 (506 MHz CF). Other two
multiplexes will be broadcast in the UHF band until the
end of May 2017, so we expect an increase in total RF
exposure associated with this technology.
Transmitter
2
1
Fig. 2. Indication of the measurement locations on the map
(yellow marker: E < 0.1 V/m; black marker: E > 0.1 V/m)
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The highest E-field level recorded during the survey
was 0.382 V/m, which represents 1.24% of the exposure
limit (30.93 V/m at the frequency of 506 MHz). It was
measured in the proximity of the “Pietraria” transmitter,
at a ground distance of about 150 m (location “1” on the
map). The highest E-field level measured in the urban
environment was 0.096 V/m (location “2” on the map),
which accounts for 0.31% of the limit.
DVB-T2
Analogue TV
LTE 800
PMR
Fig. 3. Overview of the VHF and UHF frequency bands
Fig. 4.a illustrates the general distribution of the
survey results in terms of E-field strength. The
overwhelming majority of the results are below 0.1 V/m
(0.32% of the field strength limit), whereas the average
and median values are 0.072 V/m (0.23% of the limit)
and 0.056 V/m (0.18% of the limit) respectively. In
percentage terms, 61% of the recorded E-field levels are
below 0.25% of the ICNIRP exposure limit, whereas 13%
of the readings are in the range from 0.25% to 0.5% of
the limit (Fig. 4.b).
At a first glance, the obtained results are comparable
to those reported for DVB-T in the literature. For
instance, in [7], the maximal exposure concerning the
power density is 6.5 mW/m2 (corresponding to 0.24% of
the ICNIRP reference levels), whereas our maximum
value is 0.39 mW/m2 (corresponding to 0.015% of the
ICNIRP limit, 2.53 W/m2). In [8], the maximal and
average exposure values reported for Analogue TV /
DVB-T are 1.65 V/m and 0.09 V/m respectively. As we
can see, these levels are somewhat higher than our
results, but we measured only a single channel.
37
32
5
12
0
21
0
5
10
15
20
25
30
35
40
0-0.05 0 .05-0.1 0.1-0.1 5 0.15-0 .2 0.2-0 .25 0.2 5-0.3 0.3-0.35 0.35-0 .4
E-Field Str ength (V/m)
Number of Measurements
a)
61
13
123
0
10
20
30
40
50
60
70
0%-0.25% 0.25%-0.5% 0.5 %-0.75% 0.75%-1% 1%-1.25%
% of Expo sure Limit
% of Measur ements
b)
Fig. 4. Distribution of the recorded data: a) number of
measurements as a function of E-field strength; b) percent of
measurements as percent of ICNIRP exposure limit
Regarding the main factors influencing the DVB-T2
exposure, this greatly depends on the distance from the
transmitter and terrain irregularities. The buildings and
other obstructing structures in the urban environment
have also a strong influence on the DVB-T2 exposure,
causing not only a significant reduction in the EMF
levels, but also a very complex spatial distribution.
V. CONCLUSIONS AND FUTURE WORK
According to the measurements performed for this
survey, the E-field levels from DVB-T2 transmitter
antennas were found to be well bellow the exposure
limits recommended in the ICNIRP guidelines. The
highest E-field level was 0.382 V/m, which corresponds
to only 1.24% of the exposure limit, whereas 74% of the
measurements were below 0.5% of the limit.
Future research will be focused on the influence of
different factors on the DVB-T2 exposure. For instance,
one limitation of our study was that most of the
measurements were taken outdoor, at the ground level, so
further investigations might be necessary to characterize
the indoor exposure, especially in tall buildings that are in
the direct line-of-sight of the transmitter. Also, we expect
an increase in the total DVB-T2 exposure with the release
of MUX2 and MUX4, until the end of May 2017.
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