Population density effect on radio frequencies

Population density effect on radio frequencies interference (RFI) in radio astronomy Roslan Umar, Zamri Zainal Abidin, Zainol Abidin Ibrahim, Mohd Saiful Rizal Hassan, Zulfazli Rosli, and Zety Shahrizat Hamidi Citation: AIP Conference Proceedings 1454, 39 (2012); doi: 10.1063/1.4730683 View online: http://dx.doi.org/10.1063/1.4730683 View Table of Contents: http://scitation.aip.org/content/aip/proceeding/aipcp/1454?ver=pdfcov Published by the AIP Publishing

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Population Density Effect on Radio Frequencies Interference (RFI) in Radio Astronomy Roslan Umar1,2*, Zamri Zainal Abidin1, Zainol Abidin Ibrahim1, Mohd Saiful Rizal Hassan1, Zulfazli Rosli1 and Zety Shahrizat Hamidi1,3 1

Department of Physics, Faculty of Science, University of Malaya, 50603, Kuala Lumpur, Malaysia 2 Astronomy Unit, Universiti Sultan Zainal Abidin (UniSZA), 21300, Kuala Terengganu, Malaysia 3 Faculty of Applied Sciences, University Teknologi Mara, 40450, Shah Alam, Malaysia *[email protected]

Abstract. Radio astronomical observation is infected by wide range of Radio Frequency Interference (RFI). We will also use information gathered from on-site RFI level measurements on selected 'good' areas generated by this study. After investigating a few suitable sites we will commence to the site and construct the RFI observation. Eventually, the best area we will be deciding from the observations soon. The result of this experiment will support our planning to build the first radio telescope in Malaysia. Radio observatories normally are located in remote area, in order to combat RFI from active spectrum users and radio noise produced in industrial or residential areas. The other solution for this problem is regulating the use of radio frequencies in the country (spectrum management). Measurement of RFI level on potential radio astronomical site can be done to measure the RFI levels at sites. Seven sites are chosen divide by three group, which is A, B and C. In this paper, we report the initial testing RFI survey for overall spectrum (0-2GHz) for those sites. The averaged RFI level above noise level at the three group sites are 19.0 (±1.79) dBm, 19.5 (±3.71) dBm and 17.0 (±3.71) dBm and the averaged RFI level above noise level for without main peaks are 20.1 (±1.77) dBm, 19.6 (±3.65) dBm and 17.2 (±1.43) dBm respectively. Keywords: Radio Astronomy, Radio Frequency Interference (RFI) and Spectrum Management PACS: R 95.45. +i

INTRODUCTION The use of radio-frequency for telecommunications equipment is dramatically increasing, and one consequence is that background levels of radiofrequency interferences are increasing over much of the Earth’s land surface. Radio astronomy telescopes are very sensitive instruments of the radio-frequency background levels as they use the most sensitive radiowave receivers in the world [1]. It is becoming increasingly important for radio telescopes to be located in the remote areas where the background levels of radio-frequency interferences are low. There is international interest in looking for one or more radio-quiet reserves on the Earth. A radio-quiet reserve is an area where the levels of radio-frequency interferences are low, and over which regulatory or legislative protection controls the increase in radiofrequency interferences. This situation called Radio Quite Zone (RQZ) [2-4]. There are two solutions to address this problem, firstly create a RQZ. A possible

answer may be to the conflicting requirements of radio astronomy or telecommunications industry is to identify and protect a few “RFI-free” areas on Earth, for example areas with very low levels of RFI, where radio astronomy observation requiring radio-quietness could be conducted. Secondly is move away from the city which is looking for RFI free areas. So area’s low population density in the interior means that there are relatively has low levels of radio frequency emission. So that areas may possess appropriate locations for radio astronomy and other facilities requiring radioquietness. By using information from the Malaysian Communications (MCMC) Authority database, comprising a comprehensive listing of all radio licenses for the Malaysian continent, estimates have been made of radio-frequency levels for various locations [5]. It should be noted that the database is a listing of licenses only. Actual transmitters may not be in place all the time and may not be operational all the time.

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POPULATION EFFECT ON RFI Human-made RFI are still one of the main threats in the selection of suitable sites for radio astronomy observation and the installation of new radio telescopes sources in our country. So that the main parameter has to consider for radio astronomy observation is population density. RFI-free areas means very low RFI and RFI is proportion with population density of the citizen. Population was selected as the parameter because RFI is basically caused by the human being indirectly. In this research we categories population density into 3 groups. Group A (0-200) is classified low the population density. In table 1 we can see that 65 % of radio telescope in the world was built at sites with population density in group A. However 20% are in group B (200-600) and only 15% are built in Group C (600 and above). Group C is around high RFI land sites as shown on Table 2. TABLE 1. Population density for several main telescopes in the world Location of Radio Telescopes Population density (peoples/km2) South Africa, HartRAO, ( 26m

586.8

China, Delingha, (13.7 m)

7.48

Japan, Nobeyama, (45 m)

158.14

Australia, Parkes, (64m)

9.04

research study we use frequency range 1420MHz (21cm, hydrogen line). The discone antenna is connected to a low noise amplifier (LNA) 3GHz spectrum analyzer and coaxial cables. Antenna is crucial part in this RFI observation because it receives the signal from surrounding area. Copper have been chosen as material to build a discone due to its rust resistance and flexibility at every chosen site. Observations of the RFI are taken in an interval of 15 minutes. Survey was done at every site covering the wide bands for a 24hour [2-4]. This is done to see how the RFI vary over a long stretch of time. The results mesured RFI value for both with and without main peaks for several sites with different in population density shown on Table 2. After that we compare to each other to determine which site has lowest RFI as well the best site for radio telescope.

RESULT AND ANALYSIS TABLE 2. Average RFI survey for selected sites. Sites

Meteorology Station UM Physics Dpt. Lubuk Cina Langkawi

-83.054

Average level Without peaks (dBm) -84.264

6030

-86.290

-87.384

250 215

-97.777 -97.734

-98.259 -97.801

Population density (peoples/km2)

7020

Average level (dBm)

German, Effelsberg, (100m)

152.9

United States, VLA (27 x 25 m

6.27

United State, GBT (100 m)

29.0

Merang Kg. Sekayu

47 19

-100.375 -100.242

-100.374 -100.242

England, Jodrell Bank,( 76 m)

429

Kg. Bertam

13

-98.4828

-100.242

China, Nanshan (25m)

283

Puerto Rico, Arecibo, (306 m)

430

Australia, ASKAP

0.91

United State, SMA

72.83

South Africa, MeerKat

2.8

Australia, Mount Pleasant

895

German, Stockert (25m)

122

India, GMRT, (30 x 45 m)

7,214

Poland, Toruń RT3 (15 m)

1,779.6

New Zealand, Warkworth (12

29.3

United State, VLBA

6.27

TABLE 3. Average RFI level above noise level with different population density Average RFI Average Group Population RFI level level (dBm) density Without (dBm) (peoples/km2) peaks A 0 - 200 19.0 20.1 (±1.77) (±1.79) B 200 – 600 19.5 19.6 (±3.65) (±3.71) C 600 and above 17.0 17.2 (±1.43) (±3.71)

METHODOLOGY In order to identify the RFI value, we use several instruments such as a copper discone antenna (in our


FIGURE 1. RFI profile with main peaks.

population density normally demand to the good facility and high technology (commercial user) and will produces more RFI. Man-made RFI is main threat to the astronomer. RFI basically troubling astronomical observations in many ways for example harmonics and inter-modulation products due to nonlinear devices in high power transmitter and also with unwanted out of windows adjacent and nearby windows, which are frequently due to the lack of adequately sharp filter in our transmitter. In order to external limit RFI we need move away from residents as far as we can. However there are internal RFI also important thing need to consider for example electric and electronic components operate in our telescope and computer. Therefore for the future we need more effort to shield radio telescope from RF emission.

CONCLUSION AND DISCUSSION We can conclude that Radio telescopes should be built on area which has population density from 0 – 200 (group A) peoples per square kilometre (Table 2). The decision is made because we can see that average RFI level decreases due to low population density. For the future observation, we suppose to find a new technique and go more sites to do RFI observation to discover more suitable locations in order to do radio astronomy observation. RFI mapping with a new technique may be a best choice into this research. FIGURE 2. RFI profile without main peaks. The averaged RFI level above noise level at the three group sites are 19.0 (±1.79) dBm, 19.5 (±3.71) dBm and 17.0(±3.71 dBm and the averaged RFI level above noise level for without main peaks are 20.1 (±1.77) dBm, 19.6 (±3.65) dBm and 17.2 (±1.43) dBm respectively (Table 3).

ACKNOWLEDGMENTS Authors would like to thank the University of Malaya for their grants used for this research, University Sultan Zainal Abidin (UniSZA) supported scholarship for further in this study and data support from Department of Statistics Malaysia. Also thanks to our Radio Cosmology Research Laboratory, Syed Bahri, Norwati, Ungku Ferwani Salwa, Norsiah, Nor Suzian, Nor Alia, Mohd Ashraf, Noor Khalaf and Siti Fatinah and also last but not least staff laboratory Mohd Raihan and Mohd Khairi, for their helps and advice.

REFERENCES

FIGURE 3. RFI profile with population density.

The relationship between population and the strengh of RFI is very interesting to discussed. As we can see in figure 3 as we move to high density sites, the averaged RFI level rapidly amplify. Sites with high

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