The electromagnetic spectrum from 1 Hz to 9.4 GHz

near ground level in the region of Siio Jose dos

Campos, SP, Brazil

Imicio Malmonge Martin and Mauro A. Alves Department of Physics

Technology Institute of Aeronautics Sao Jose dos Campos, SP, Brazil

martin@ita.br and mauro.a.alves@gmail.com

Abstract- In the period from June 2012 to May 2013 measurements of the electromagnetic spectrum from 1 Hz to 9.4 GHz were collected in Siio Jose dos Campos, SP, Brazil. At this

site, the electromagnetic spectrum is produced by both natural

and artificial sources. The intensities of the electric and magnetic

fields were measured in two frequency ranges (1 Hz to 1 MHz,

and 1 MHz to 9.4 GHz) with hand-held detectors and compact

antennas. Measurements were performed in sweep-time mode

and changing precision in the resolution bandwidth (RBW).

Main peaks in the spectrum correspond to Schumann resonances

at 7.8, 14, 20 and 33 Hz, emissions by power lines, radio

frequencies, navigational radio beacons, mobile phone and Wi-Fi

systems, C- and X-band radars (ground stations and on board aircraft).

Keywords- electromagnetic waves, non-ionizing radiation, electric field, magnetic field, environmental radiation.

I. INTRODUCTION

The power of non-ionizing environmental radiation (electromagnetic waves) in a region is measured in dBm, the intensity of the electric field (E) in V 1m and the intensity of the magnetic field (B) in teslas. These quantities often vary with frequency as cosinusoidal functions, e.g., E(x, t) = Emcos (wt-lex) and B(z, t) = Bmcos (wt-kz) where Bm and Em are the maximum values of the electric and magnetic fields, respectively, k is the wave number, w is the angular velocity of the waves and x is the direction of propagation [1]. Frequency spectrum analyzers can record the intensity of electromagnetic radiation in a given frequency band or perform measurements at pre-determined frequency values. There are in the market several models of frequency spectrum analyzers that make measurements over broad frequency ranges (from 10 kHz up to 26 GHz). But these instruments are usually expensive and can be used only in a laboratory setting because of their lack of portability; additionally, they do not have sensitivity to observe radiation when the power is less than -100 dBm and require several antennas to perform measurements over different frequency bands.

Electromagnetic radiation is represented by waves that

This study received financial support from CNPq (Procs. 480407/2011-8 and 305145/2009-6).

978-1-4799-1397-8/13/$31.00 ©2013 IEEE

Marcelo Pego Gomes Division of Atmospheric Sciences Institute of Aeronautics and Space Sao Jose dos Campos, SP, Brazil

Gomesmpfis@yahoo.com.br

propagate through space. These waves are formed by the sum of an electric field (E) and magnetic field (B), which vary in time and space, and oscillate at right angles to one another. The direction of propagation corresponds to the displacement of energy [J/,uo (ExB), Poynting vector] [1]. These radiations include ultraviolet (near visible), visible light, infrared, ELF (Extremely Low Frequency), LF (Low Frequency), VHF (Very High Frequency) and microwaves. The frequency band ranging from 3 kHz to 300 GHz is known as the radio frequency (RF) band [2].

Radio and television operate on frequency bands ranging from 300 kHz to 300 MHz (radio and television) and 470 MHz to 806 MHz (television). Electric currents also produce alternating electromagnetic fields around conductors and other equipment; in Brazil, the oscillation frequency of the alternating current is 60 Hz. The microwave band ranges from 300 MHz to 300 GHz; 300 GHz (far infrared) is the threshold of the visible light spectrum [2,3]. Mobile phones operate in several microwave bands: 900 MHz for analog mobile phones, l.8 to l.9 GHz for GSM (Group Special Mobile) phones, 2.45 GHz for 3G phones, and more recently around 3.5 GHz for WiMAX (Worldwide Interoperability for Microwave Access) phones. The C-band (6 GHz) and KU-band (14 GHz) are used in special situations such as tracking of trucks and satellite communications [4]. Weather radars, on-board aircraft radars, and search-and-rescue radars operate on frequencies ranging from 2 to 12 GHz [5]. Frequencies around 8 GHz are used for the transmission of data between satellites and ground stations [4]. Industrial equipment and machines operating at frequencies ranging from 20 to 40 MHz are also sources of electromagnetic radiation [6,7].

Because of the diversity of sources of electromagnetic radiation in the environment, the main objective of this paper was to record and identify the main features (natural and human-made) of the electromagnetic spectrum from 1 Hz to 9.4 GHz, with a frequency resolution of 1 Hz and sensitivity of - 170 dBm in the region of Sao Jose dos Campos, SP, Brazil. To the best of our knowledge, this is the first time that measurements in this frequency range have been collected in

this region; hence the data presented in this study can provide important information regarding the future use and allocation of frequency bands and other technical applications.

II. MATERIALS AND METHODS

Two solid-state, battery-operated (8 hours continuous operation), hand-held spectrum frequency analyzers were used to collect data: Spectran NF (Aaronia AG, Germany) for the frequencies bands ranging from 1 Hz to 1 kHz, and from 1 kHz to 1 MHz and Spectran HF (Aaronia AG, Germany) for the frequency band ranging from 1 MHz to 9.4 GHz. A compact omnidirectional antenna was used for all measurements; a compact directive antennae was also used with the Spectran HF. Sampling time, from 5 to 300 ms, can be chosen by the user, and the resolution bandwidth (RBW) ranges from 1 Hz to 300 MHz. The sensitivity of the Spectran HF is - 170 dBm between 1 MHz and 9400 MHz; the sensitivity of the Spectran NF is on the order of a few nanovolts between 1 Hz and 1 MHz. Data acquisition is carried out through a software that shows the data on the instrument's display and stores them. The collected data can be transferred to a computer for further analysis. Since the system is compact and portable, it is possible to perform measurements in remote places under different environmental conditions.

The measurements were performed in 2012 and 2013 in Sao Jose dos Campos, SP, Brazil, at the campus of the Instituto Tecnol6gico de Aeromiutica (ITA), in the morning or afternoon, always at the same location and over the whole frequency range of operation of the analyzers (1 Hz to 9.4 GHz). Data were collected during the dry season (June to August) and rainy season (September to December) in 2012, and during the rainy season (January to April) in 2013.

III. RESULTS AND DISCUSION

Measurements of the local electric field intensity in the frequency range from 1 to 40 Hz are shown in Fig. 1. Four peaks at 7.8, 14, 20 Hz and 33 Hz corresponding to Schumann resonance frequencies can be identified. The data were collected on 02/20/2013, 14:45 h local time, during heavy rainfall. Schumann resonances are quasi-standing electromagnetic waves excited by lightning discharges. These waves are present in Earth's atmosphere, between the surface of the planet and the densest part of the ionosphere [8].

The spectrum of the local electric field intensity from 1 Hz to 1 kHz is shown in Fig. 2. In this region of the spectrum, the average background field intensity is about 40 V 1m. Few emission peaks are present, but two peaks produced by power lines (an important source of electromagnetic pollution) can be identified at 60 Hz (730 Vim) and 120 Hz (500 Vim). Other minor peaks with amplitudes between 4 and 12 Vim are also present and are probably produced by RF emissions or whistler waves.

The spectrum of the local electric field intensity from 1 kHz to 1 MHz is shown in Fig. 3. In this figure, four peaks at

128.20, 384.55, 641.05 and 897.55 kHz (intensities between 12 and 2 Vim) stand out against the background. This region of the spectrum corresponds to low and medium frequency radio frequencies used for AM radio broadcasting, information, and weather systems, and navigational radio beacons.

The spectrum of the local electric field power from 1 MHz to 9.4 GHz is shown in Fig. 3. In this frequency range, the average power of the background radiation is about -50dBm.

0.10 ..,......----_----------------,

0.09

E :> 0.08

� :2 0.07 .21 u..

u

'E 0.06 u .2:! W 0.05

0.04

0.03 +---.----.-....--r---.-----,_-.---.----.-r-.......---r----.-........... o 5 10 15 20 25 30 35

Frequency (Hz)

Fig. I. Experimental observation of Schumann resonance frequencies at 7.8, 14, 20 and 33 Hz. Data collected in 02/20/2013, 14h 45 min local time, during rainfall.

800 60Hz

700

600 t20Hz

� �5II0 "C ;; u: �o u ." U � 300

200

100

u u � u " � U U U U Frequency (kHz)

Fig. 2. Spectrum of the local electric field intensity from 1 Hz to 1 kHz. Data collected in July 2012.

The spectrum exhibits several distinct features: from 1 MHz to 2 GHz the spectrum is crowded with frequency peaks

produced by VHF signals and mobile phone systems, from 2 GHz to 5 GHz the peaks are produced by Wi-Fi emissions; at 8 GHz there is a peak produced by transmissions between ground stations and satellites; strong peaks at 6 GHz, produced by aircraft radars (C-band) the C-band have been recorded in some occasions; peaks between 8 GHz and 9.4 GHz are produced by meteorological radars (X-band) on board aircraft. These emissions change in time and in intensity because the distances between aircraft and the measuring devices are constantly varying.

·20 Mobile phones VHF

X-band radars

� � � � � � 00 � m Frequency (MHz)

Fig. 3. Spectrum of the local electric field intensity from I kHz to I MHz. Data collected in July 2012.

t4r--------------------------------------,

� �

12

10

1J 8 Cii u: u :s 6 u '" iij

128,20 kHz

384,55 kHz

641.05 kHz

a tOO 200 300 400 500 600 700

Frequency (kHz) 800 sao tOOO

Fig. 4. Power spectrum of the local electric field from J MHz to 9.4 GHz. Sweep time was 50 ns and RBW was I MHz. Data were collect in January 2013.

The changing characteristic of the spectrum is illustrated in Fig 5. Nine spectra, from 1 MHz to 9.4 GHz, were recorded on 03/23/2013 between 7 h 39 min and 8 h 15 min, local time. At the time of data acquisition, no strong emissions were detected in the spectral region corresponding to radars operating in the C-band; on the other hand, there is an observable change in the amplitude and position of peaks between 8 GHz and 9.4 Hz.

-30 8:15

·90

-30 8:10

·90

-30 8:05

·90

-30 7:58

E co ·90

� "- -30 7:53 CD � 0 ·90

Q.

-30 7:48

·90

·30 7:42

·90

-30 7:41

·90

·30 7:39

·90

1000 2000 3000 4000 5000 6000 7000 8000 9000 Frequency (MHz)

Fig. 5. Time variation of the power spectrum of the local electric field from I MHz to 9.4 GHz. Data were collected in 03/23/2013, from 7 h 39 min to 8 h J 5 min, local time.

IV. CONCLUSION

Spectra of environmental electromagnetic radiation were collected with a portable and compact set of instruments and antennas in the frequency range from 1 1 Hz to 9.4 GHz, in the region of Sao Jose dos Campos, SP. Several interesting features were observed in the spectra: Schumann resonances, peaks at 60 Hz and 120 Hz produced by power lines; peaks between 120 KHz and 900 KHz produced by radio broadcasting, navigational radio beacons; in the frequency range from 1 kHz to 1 MHz there are a number of low­amplitude peaks produced by whistler waves; peaks produced by systems for communications with satellites; in the frequency range from 1 MHz to 9.4 GHz, the electromagnetic spectrum is very diverse, with peaks produced by VHF signals, mobile phones and Wi-Fi systems, radars operating in

the C- and X-bands. The measurements also show the crowding and pollution in the electromagnetic spectrum produced by these different sources of electromagnetic radiation.

Although the main objective of this study was to characterize the electromagnetic spectrum in the region of Sao Jose dos Campos, this study shows the importance of the monitoring of electromagnetic spectrum because of the constant growth of devices that use a sizable fraction of the spectrum; additionally, this type of survey using compact instruments can be used in an educational setting to help students better understand the concepts related to data acquisition and the importance of a complete knowledge of the spectrum of electromagnetic radiation for proper use and future allocation of frequency bands.

ACKNOWLEDGMENT

To Fortunato R. Guimaraes for providing the spectral analyzers and to the Instituto Tecnologico de Aeromiutica (IT A) for the technical and logistical support.

REFERENCES

[I] C. A. Balanis, Advanced Engineering Electromagnetics. New York: John Wiley & Sons, 1989, pp 104-129.

[2] L. W. Barclay, The Propagation of Radiowaves, 2nd ed. London: The Institution of Engineering and Technology, 2003, pp. 1-9.

[3] Anatel. Regulamento sobre Iimitavao da exposivao a campos eletricos, magneticos e eletromagneticos na faixa de radiofrequencias entre 9 kHz e 300 GHz. Anexo it resoluvao n.o 303 02 de Julho de 2002. Disponivel: http://www.anatel.gov.br/PortaliexibirPortallnternet.do.

[4] J. E. Allnutt, Satellite to Ground Radiowave Propagation, 2nd ed. London: The Institution of Engineering and Technology, 20 II, pp. 10-16.

[5] M. A. Richards, J. A Scheer and W. A. Holm, Principles of Modern Radar. Edison: SciTech Publishing, 20 I 0, pp. 3-56.

[6] C. Bianchi and A. Meloni, "Natural and man-made terrestrial electromagnetic noise: an outlook," Annals of Geophysics, vol. 50, pp. 435-445, June 2007

[7] O. Staub, "Indoor propagation and electromagnetic pollution in an industrial plant," 23rd International Conference on Control and Instrumentation (IECON 97), vo1.3, pp. 1198 - 1203,1997.

[8] M. Balser and C. Wagner, "Observations of Earth-ionosphere cavity resonances," Nature, vol. 188, pp. 638-641, November 1960.