The Mobile Laboratory for Radio-Frequency Interference Monitoring at the Sardinia Radio Telescope

11. D. E. Acuna, S. Allessina, and K. P. Kording, “Future 21. Peer Review in Scientifi c Publications, Science and Impact: Predicting Scientifi c Success,” Nature, 489, pp. 201- Technology Committee, House of Commons, UK, July 18, The Mobile Laboratory for Radio-Frequency 202. 2011 (http://www.publications.parliament.uk/pa/cm201012/ cmselect/cmsctech/856/85602.htm). 12. S. Alonso, F. Cabrerizo, E. Herrera-Viedma, and F. Herrera, Interference Monitoring at the “h-Index: A Review Focused in its Variants, Computation and 22. Swedish Research Council, Quality Assessment in Peer Standardization for Different Scientifi c Fields,” Journal of Review, November 5, 2009 (www.cm.se/webbshop_vr/pdfer/ Sardinia Radio Telescope Informetrics, 3, 2009, pp. 273-289. 2011_01L.pdf).

13. G. F. Gaetani and A. M. Ferraris, “Academic Promotion in 23. European Physics Society, “On the Use of Bibliometric Pietro Bolli1, Francesco Gaudiomonte1, Roberto Ambrosini2, Claudio Bortolotti2, Mauro Italy,” Nature, 353, 1991, pp. 10. Indices During Assessment,” http://c.ymcdn.com/sites/ www. 2 3 3 eps.org/resource/collection/B77D91E8-2370-43C3-9814- Roma , Carlo Barberi , and Fabrizio Piccoli 14. P. Lawrance, “The Politics of Publications,” Nature, 422, 250C65E13549/EPS_statement_June2012.pdf. 1National Institute of Astrophysics – Astronomical Observatory of Cagliari 2003, pp. 259-261. Capoterra (Cagliari), Italy 24. http://www.ieee.org/publications_standards/publications/ Tel: +39-070-71180226; Fax: +39-070-71180222; E-mail: pbolli@oa-cagliari.inaf.it 15. P. Lawrance, “The Missmeasurement of Science,” Current journmag/journalcitations.html. Biology, 17, 15, 2007, p. R583-R585. 2National Institute of Astrophysics – Institute of Radio Astronomy 25. http://altmetrics.org/manifesto/. Bologna, Italy 16. F. Guilak and C. R. Jacobs, “The h-Index: Use and Overuse,” Journal of Biomechanics, 44, 2011, pp 208-209. 26. P. Campbell, “Escape from the Impact Factor,” Ethics in 3Offi cina Meccanica G. Barberi Science and Environmental Politics, 8, 2008, pp. 5-7. Sesto Calende (Varese), Italy 17. A. Abbott , D Cyranoski , N. Jones , B. Maher, Q. Schiermeier, and R. Van Noorden, “Metrics: Do metrics Matter?,” Nature, 27. P. O. Seglen, “Why the Impact Factor of Journals Should 465, 2010, pp. 860-862. not be Used for Evaluating Research,” BMJ, 314, February 15, 1997. 18. National Health and Medical Research Council, Australia, April 2010, “NHMRC Removes Journal Impact Factor from 28. P. O Seglen, “Causal Relationship Between Article Abstract Peer Review of Individual Research Grant and Fellowship Citedness and Journal Impact,” Journal of the American Society Applications,” http://www.nhmrc.gov.au/_fi les_nhmrc/fi le/ for Information Science, 45, 1994, pp. 1-11. grants/peer/impact%20factors%20in%20peer%20review.pdf . In this paper, a quite unique mobile laboratory for monitoring radio-frequency interference with a radio-astronomical 29. “San Francisco Declaration on Research Assessment observatory is described. The unit is fully operational at the new Sardinia Radio Telescope, a 64-m antenna now in 19. Institut de France, Académie des Sciences, “On the Proper (DORA),” 2013, http://am.ascb.org/dora/. the commissioning phase in Italy. The mobile laboratory is mainly used to identify the source of interference with the Use of Bibliometrics to Evaluate Individual Researchers,” radio astronomy service using iterative triangulations in the azimuth directions. Both the design and realization of 17 January 2011, http://www.academie-sciences.fr/activite/ this prototype were handled with outstanding care to limit the emission of self-interference as much as possible. The rapport/avis170111gb.pdf . laboratory was equipped with excellent microwave instruments in terms of sensitivity, frequency coverage, dynamic range, and various demodulation and signal-analysis facilities. The unit can be quickly switched to different RF and 20. European Science Foundation, European Peer Review power-supply confi gurations, while offering operators a safe and effi cient workplace, even in adverse meteorological Guide, Integrating Policies and Practices for Coherent and driving conditions. In the past months, the mobile laboratory has proven to be successful in detecting and identifying Procedures, March 2011 (http://www.esf.org/activities/mo- many radio interferers. Two examples of measurement campaigns are described. fora/peer-review.html). Keywords: Radio astronomy; radio spectrum management; radio frequency interference; electromagnetic compatibility; radiowave propagation

1. Introduction objective requires fi rst the absolutely mandatory “a priori” activity dedicated to the regulatory management of the radio adio waves coming from the far universe reach the Earth spectrum on all scales: international, regional, and local (for Rwith power levels many orders of magnitude lower than example, with the defi nition of a radio-quiet zone around the manmade radio signals. For instance, a 1 Jy spectral power fl ux telescope site). Second, a proper continuous RFI monitoring density (where Jy stands for the astronomical unit called a activity is also crucial to assure optimal operation of a radio Jansky, equivalent to 10−26 W/m 2 /Hz , frequently used in the telescope. Such activity implies different tasks, and offers many context of radio astronomy) is considered to be a strong celestial benefi ts: source, as compared with the usual targets of radio-astronomical observations. All the radio observatories therefore spend a lot • The early identifi cation of any new signal not of effort trying to keep their sites as quiet as possible, keeping complying with the International Telecommunication away any radio-frequency interference (RFI). Obtaining this Union (ITU) regulations. RFI occurring in the

AP_Mag_Oct_2013_Final.indd 19 12/15/2013 3:53:11 PM frequency bands allocated to the radio astronomical due, for example, to multipath refl ections from surrounding usage, as outlined in Figure 3. The van walls were internally service (RAS) has to be reported, with its obstacles, and consequent wasting of time. Moreover, in all covered with thermally insulating panels. An auxiliary air- (experimentally detected) harmful characteristics, cases when the interferer is barely detectable, the possibility conditioning system for either cooling or heating and ergonomic to the national administration. of driving closer to origin of the radio emission or into the seats assured safe and good comfort for a maximum of two line of sight (such as the top of a mountain) allows greatly operators. Additionally, two photovoltaic cells were installed in • The statistical evaluation of the actual spectral improving the signal-to-noise ratio until a solid identifi cation the roof of the van to provide power for ventilating the inside occupancy in other frequency bands, not allocated can be guaranteed. It is indeed worthwhile noting that the air volume, thereby preserving the electronic instruments from to the radio astronomical service, can be utilized fi nal sensitivity of a large radio telescope – with cryogenically dangerously hot temperatures in the summertime. to increase the receivers’ bandwidths, and then cooled, state-of-the-art microwave receivers, integrating signals to improve the sensitivity of the passive radio- for hours over extremely wide bandwidths – can be many orders The aluminum retractable telescopic mast can lift one astronomical observations. of magnitude higher than the level obtainable by a high-quality antenna and the front-end box a maximum height of 11 m. It commercial RF receiving chain, such as the chain we have in can be rotated in azimuth either electronically, under computer • The dynamic range of the radio-astronomical the mobile laboratory. control, or manually (much faster). An electronic compass receivers can be improved by selecting amplifi er displays the azimuth angle of the antenna’s pointing. A second gains, fi lter characteristics, and conversion schemes The decision to provide the Sardinia Radio Telescope motor at the top of the mast can rotate the antenna, selecting suitable to match the real RF environment receivable (SRT) with this kind of mobile station came after the decade either horizontal or vertical polarization. All the devices to at the observatory site. of operational experience gained with a similar unit developed be installed on the top of the mast are provided with a quick for the Medicina radio-astronomical observatory, located in mechanical interface to speed up the operation of switching • This last knowledge can also allow identifying Northern Italy, close to the city of Bologna [2, 3]. from one confi guration to another. After stopping the vehicle, the operational parameters and strategies that best four electro-hydraulic jacks automatically horizontally level the optimize the effi ciency of applying mitigating In this paper, we give a general overview of the mobile van in such a way that the mast can be safely raised. techniques to make astronomical observations more laboratory in Section 2. Section 3 describes the antennas and effi cient. On this subject, see the proceedings of the microwave front ends, while Section 4 deals with the back ends The upper operational frequency limit of the RF receiving RFI mitigation workshop held in Groningen, the used for data processing. Finally, Section 5 describes two short system is 18 GHz under normal conditions, but with minor Netherlands, on March 29-31, 2010, published in examples of RFI campaigns recently performed. the Proceedings of Science [1].

• Finally, to dynamically schedule the radio astronomical observations according to statistically 2. RFI Mobile Laboratory signifi cant evaluations of the expected “lack” of Figure 1. A general view of the Sardinia Radio Telescope site interference at particular times (for instance, on The Sardinia Radio Telescope is a new facility, close to in December 2011 (Gianni Alvito, INAF-OAC). nights or weekends). its fi nal commissioning [see the postscript at the end of this article]. The antenna is a fully steerable, wheel-and-track As a matter of fact, each radio observatory then has to defi ne parabolic dish, 64 meters in diameter, located 35 km north of the its own RFI-monitoring strategy. Some radio observatories city of Cagliari, on the island of Sardinia, Italy (see Figure 1). decide to develop ad-hoc hardware fully dedicated to this The original scientifi c and technical idea of the project was task; some others prefer to address a small percentage of the proposed and since then continuously guided by the Italian recently equipped with a dedicated mobile laboratory for RFI observing time of the radio telescope to accomplish the RFI- Institute for Astrophysics (INAF). Funding came fi rst from the measurements (Figure 2). monitoring activity. The latter option has the advantage of using Italian Ministry of Education, University and Research; then the highly sensitive radio-astronomical receivers to identify the from the Italian Space Agency; and fi nally from the Regional Having in mind to safely operate the mobile laboratory RFI, but, on the other hand, subtracting the extremely expensive Sardinian Government, this last supporting most of the local even in hostile weather conditions, as well as to be able to drive telescope time from the astronomical science. infrastructural activities. over bad terrain conditions such as unpaved roads, a Mercedes Sprinter 318 four-wheel drive vehicle with a powerful engine A step ahead is represented by a combination of a dedicated The Sardinia Radio Telescope is intended to be a general- and low gears was selected. Additionally, the truck’s mechanical RFI fi xed station, operating automatically and remotely in order purpose scientifi c facility for studies in astronomy, geophysics, structure assured a wide, full-human-height internal room, to guarantee continuous 24 hours-per-day and seven days-per- and space science. One of the most advanced features of the offering good comfort to the operators. week data acquisition, with a mobile laboratory fully equipped Sardinia Radio Telescope is the “active surface.” This means with RFI-detecting instrumentation. The capability to make that the shape of the primary mirror can be optimized at all From the radio receiving point of view, two priority design many “measure and go” surveys from different locations with elevation angles by a thousand remotely controlled actuators drivers were considered: very high sensitivity, together with a the mobile station has proven to be remarkably effi cient in [4]. In the fi nal confi guration, the Sardinia Radio Telescope large linear dynamic range. Another essential design aspect tracking, in a spiral way, the source location of the interferer. The will be equipped with approximately 20 cryogenically-cooled was to limit the generation of radio self-interference as much as two stations, fi xed and mobile, also allow making triangulations radio-astronomical receivers, remotely selectable to cover possible, mainly by properly shielding the electronic equipment in a dynamic way while monitoring the RFI from both stations the bandwidth from 0.3 GHz up to 115 GHz. The last public and selecting devices with low RFI impact. in real time. The triangulation is performed by repeating, from description of the status of the Sardinia Radio Telescope many different parked locations of the van, the search for the construction dates back to 2008, by Tofani et al. [5], while The vehicle’s internal transformation was made by azimuth angle that gives the maximum fi eld strength of the the current information of the project is available online at the Offi cine G. Barberi [6], which created three different working interferer under investigation. Thanks to a remote-controlled Sardinia Radio Telescope Web site, http://www.srt.inaf.it. areas (the driver’s cab, the operations room, and the warehouse) system, it is also possible to rotate the antennas located at with furniture made of aluminum, keeping the total weight at Figure 2. The mobile laboratory with the telescope pole at the fi xed station from inside the van, as well as to display the In order to operate the Sardinia Radio Telescope since its a minimum. All instruments were permanently mounted on 8 m height and the log-periodic dipole antenna together power spectrum received there. This avoids false identifi cations fi rst light in a radio-quiet environment, the observatory was specifi c anti-shock racks, so as to be always ready for their with the front end installed over it.

20 IEEE Antennas and Propagation Magazine, Vol. 55, No. 5, October 2013

AP_Mag_Oct_2013_Final.indd 20 12/15/2013 3:53:11 PM frequency bands allocated to the radio astronomical due, for example, to multipath refl ections from surrounding usage, as outlined in Figure 3. The van walls were internally service (RAS) has to be reported, with its obstacles, and consequent wasting of time. Moreover, in all covered with thermally insulating panels. An auxiliary air- (experimentally detected) harmful characteristics, cases when the interferer is barely detectable, the possibility conditioning system for either cooling or heating and ergonomic to the national administration. of driving closer to origin of the radio emission or into the seats assured safe and good comfort for a maximum of two line of sight (such as the top of a mountain) allows greatly operators. Additionally, two photovoltaic cells were installed in • The statistical evaluation of the actual spectral improving the signal-to-noise ratio until a solid identifi cation the roof of the van to provide power for ventilating the inside occupancy in other frequency bands, not allocated can be guaranteed. It is indeed worthwhile noting that the air volume, thereby preserving the electronic instruments from to the radio astronomical service, can be utilized fi nal sensitivity of a large radio telescope – with cryogenically dangerously hot temperatures in the summertime. to increase the receivers’ bandwidths, and then cooled, state-of-the-art microwave receivers, integrating signals to improve the sensitivity of the passive radio- for hours over extremely wide bandwidths – can be many orders The aluminum retractable telescopic mast can lift one astronomical observations. of magnitude higher than the level obtainable by a high-quality antenna and the front-end box a maximum height of 11 m. It commercial RF receiving chain, such as the chain we have in can be rotated in azimuth either electronically, under computer • The dynamic range of the radio-astronomical the mobile laboratory. control, or manually (much faster). An electronic compass receivers can be improved by selecting amplifi er displays the azimuth angle of the antenna’s pointing. A second gains, fi lter characteristics, and conversion schemes The decision to provide the Sardinia Radio Telescope motor at the top of the mast can rotate the antenna, selecting suitable to match the real RF environment receivable (SRT) with this kind of mobile station came after the decade either horizontal or vertical polarization. All the devices to at the observatory site. of operational experience gained with a similar unit developed be installed on the top of the mast are provided with a quick for the Medicina radio-astronomical observatory, located in mechanical interface to speed up the operation of switching • This last knowledge can also allow identifying Northern Italy, close to the city of Bologna [2, 3]. from one confi guration to another. After stopping the vehicle, the operational parameters and strategies that best four electro-hydraulic jacks automatically horizontally level the optimize the effi ciency of applying mitigating In this paper, we give a general overview of the mobile van in such a way that the mast can be safely raised. techniques to make astronomical observations more laboratory in Section 2. Section 3 describes the antennas and effi cient. On this subject, see the proceedings of the microwave front ends, while Section 4 deals with the back ends The upper operational frequency limit of the RF receiving RFI mitigation workshop held in Groningen, the used for data processing. Finally, Section 5 describes two short system is 18 GHz under normal conditions, but with minor Netherlands, on March 29-31, 2010, published in examples of RFI campaigns recently performed. the Proceedings of Science [1].

IEEE Antennas and Propagation Magazine, Vol. 55, No. 5, October 2013 21

AP_Mag_Oct_2013_Final.indd 21 12/15/2013 3:53:12 PM array antenna operating in the P band: this antenna resulted in Table 2. The frequency coverage, gain, and noise fi gure for 4. Microwave Back Ends and 13 elements, 2 kg weight, and 1.5 m length. Upgrades to new each channel of the receiving system, up to 18 GHz. Control System antennas with higher gain to solve for specifi c applications, Noise treating particular radio-astronomy observations, will be Frequency Gain in Figure in Inside the van, an Agilent spectrum analyzer, PSA E4446A, considered when needed. Channel Coverage Band Band together with an ICOM professional telecommunication [GHz] [dB] receiver 9500, allow identifying many characteristics of First of all, we describe the radio-frequency confi guration [dB] the signals under investigation (such as amplitude, central working up to 18 GHz (a schematic view is shown in Figure 4). A 0.30 – 0.42 36.5 – 35 4.0 – 4.5 frequency, bandwidth, type and content of their modulation, Through a very short coaxial pigtail, the antenna was connected B 1.215 – 1.805 31 – 28 4.0 – 5.0 polarization). Radio-frequency interferers are indeed of many to the front end that was located just below the polarizer and different natures: they can be either digital or analog signals, contained in a waterproof metallic box (40 cm × 40 cm × 15 cm, C 2.185 – 3.288 27.5 – 23 4.5 – 6.0 wideband or narrowband emissions, continuous wave or pulsed 7 Kg). This box hosted three RF switches, six microwave D 3.3 – 5.5 28.5 – 26 4.5 – 5.5 signals. bandpass fi lters, and the microwave Miteq amplifi er (model E 5.4 – 9.0 53.5 – 47 5.5 – 7.0 AMF-6D-00101800-35-20P). The fi lters avoided the The main RF path includes the spectrum analyzer. compression of the amplifi er, and identifi ed the six RF channels F 8.0 – 18.0 48.5 – 30.5 6.0 – 10.0 However, through a splitter, it is possible to send half of the shown in Table 2, where each bandwidth represented the points G Spare power of the signal to the ICOM receiver. This has a maximum where the S parameter of the fi lter were equal to −1 dB. 12 frequency equal to 3.3 GHz. Above this frequency, it is still possible to demodulate external signals by feeding into the A second coaxial pigtail connected the front-end output to receiver the intermediate frequency available as a further output the outer spiral coaxial cable (Sucofl ex 104), shown in Figure 5. of the spectrum analyzer. The RF signal fi nally reached the spectrum analyzer inside the van through a third coaxial pigtail. Due to the high loss of the The switches of the front-end up to 18 GHz are selectable spiral coaxial cable above 6 GHz, a Mini Circuits amplifi er through a remote controller that is located inside the van. This (model ZVA-183+) was placed at the input connector of the device also allows supplying power to the amplifi ers placed on spectrum analyzer to reduce its noise contribution in channels the top of the mast. E and F. A block diagram of the receiving system with all the devices used for channels A, B, and C is shown in Figure 4. The software interface was implemented to save the Figure 3. The inner part of the mobile laboratory. The main spectra, either in tabular form or as a plot in the computer, for workspace shown in the picture consists of two seats, one The RF system was accurately characterized by using further data processing. In the same computer, the cartography to operate the RF instrumentation and the other for the microwave instrumentation. For each frequency channel, the is run to fi nd the direction from where the interference comes. computer. gain and the noise fi gure of the whole RF chain, measured without considering the antennas but including the spectrum analyzer, are reported in Table 2. Another fundamental parameter to be considered was the 1 dB compression point, modifi cations – mainly to the RF cable connecting the top and to avoid any nonlinearity of the receiving system. This ranged bottom of the mast – it could be extended up to 40 GHz. approximately between +6 and +25 dBm, depending on the frequency at the input of the spectrum analyzer. The mobile station is self-powered by the van alternator and auxiliary batteries, in connection with inverters, to provide The outer spiral cable loss was −23.4 dB at 18 GHz. A both 12/24 V dc and sinusoidal 220 V ac at 50 Hz. A few safety radically different confi guration therefore had to be used to Figure 4. A schematic of the receiver chain with the log- interlocks disable the engine’s ignition under unsafe conditions, cover the frequency range above 18 GHz. In this setup, a low- periodic dipole array. This confi guration is valid for for example, when the telescoping mast or the leveling jacks are loss coaxial cable (Gore Phasefl ex type 0K) was used in a loose channels A, B, and C. not correctly parked. confi guration in place of the standard spiral cable. The cable was made 7 m long as a tradeoff between signal loss and the ranged between 11 dB at 18 GHz to 17 dB at 40 GHz. An Driving navigation and radio triangulations are assisted maximum height of the antenna above the ground. Cable loss by a cartography GPS system connected to a computer. Radio automatic stop of the telescoping pole was set at 8 m to prevent paths and approaching roads can then be easily selected in the breaking the cable. In this confi guration, the front-end box was most intuitive graphical form. replaced by a single amplifi er (Miteq JS42-18004000-35-5P) Table 1. The antennas available in the mobile laboratory. placed between the horn and the Gore cable. A further robust amplifi er (Miteq JS3-18004000-50-15P) found a place after the Frequency Frequency Gain in cable to reduce the noise contribution of the spectrum analyzer. Type Coverage 3. Microwave Front Ends and Antennas Bands Band [dBi] Neither pigtails nor transitions were used in this confi guration [GHz] to limit the signal loss, which would add a noise contribution. In order to cover the full frequency range from 300 MHz P band LPDA 0.29 – 0.45 11 – 12 For this frequency band, the total gain ranged from 60 to 70 dB, up to 40 GHz, four commercial antennas were selected: they L/S band LPDA 1.2 – 3.3 11 – 11.5 whereas the noise fi gure was approximately 3.5 dB. In this case, were single polarized, either log-periodic dipole arrays (LPDA) the 1 dB compression point turned out to be +17 dBm at the C/X/Ku band Dual-ridge horn 1 – 18a 6 – 16 or dual-ridged horns, with characteristics as in Table 1. The input of the spectrum analyzer. K/Ka band Dual-ridge horn 18 – 40 18 – 24 antennas can be placed, one by one, over the polarizer on the Figure 5. The RFI mobile laboratory in the foreground, top of the telescope mast. The most stringent requirements in aActually, this antenna is used in the frequency range from 3 GHz to 18 GHz, A complete technical description of the RF receiving and the Sardinia Radio Telescope pointing in the zenith terms of weight and size concerned the log-periodic dipole where the gain is between 10 dBi and 16 dBi. system, along with its characterization, was reported in [7]. direction in the background (Gianni Alvito, INAF-OAC).

22 IEEE Antennas and Propagation Magazine, Vol. 55, No. 5, October 2013

AP_Mag_Oct_2013_Final.indd 22 12/15/2013 3:53:13 PM array antenna operating in the P band: this antenna resulted in Table 2. The frequency coverage, gain, and noise fi gure for 4. Microwave Back Ends and 13 elements, 2 kg weight, and 1.5 m length. Upgrades to new each channel of the receiving system, up to 18 GHz. Control System antennas with higher gain to solve for specifi c applications, Noise treating particular radio-astronomy observations, will be Frequency Gain in Figure in Inside the van, an Agilent spectrum analyzer, PSA E4446A, considered when needed. Channel Coverage Band Band together with an ICOM professional telecommunication [GHz] [dB] receiver 9500, allow identifying many characteristics of First of all, we describe the radio-frequency confi guration [dB] the signals under investigation (such as amplitude, central working up to 18 GHz (a schematic view is shown in Figure 4). A 0.30 – 0.42 36.5 – 35 4.0 – 4.5 frequency, bandwidth, type and content of their modulation, Through a very short coaxial pigtail, the antenna was connected B 1.215 – 1.805 31 – 28 4.0 – 5.0 polarization). Radio-frequency interferers are indeed of many to the front end that was located just below the polarizer and different natures: they can be either digital or analog signals, contained in a waterproof metallic box (40 cm × 40 cm × 15 cm, C 2.185 – 3.288 27.5 – 23 4.5 – 6.0 wideband or narrowband emissions, continuous wave or pulsed 7 Kg). This box hosted three RF switches, six microwave D 3.3 – 5.5 28.5 – 26 4.5 – 5.5 signals. bandpass fi lters, and the microwave Miteq amplifi er (model E 5.4 – 9.0 53.5 – 47 5.5 – 7.0 AMF-6D-00101800-35-20P). The fi lters avoided the The main RF path includes the spectrum analyzer. compression of the amplifi er, and identifi ed the six RF channels F 8.0 – 18.0 48.5 – 30.5 6.0 – 10.0 However, through a splitter, it is possible to send half of the shown in Table 2, where each bandwidth represented the points G Spare power of the signal to the ICOM receiver. This has a maximum where the S parameter of the fi lter were equal to −1 dB. 12 frequency equal to 3.3 GHz. Above this frequency, it is still possible to demodulate external signals by feeding into the A second coaxial pigtail connected the front-end output to receiver the intermediate frequency available as a further output the outer spiral coaxial cable (Sucofl ex 104), shown in Figure 5. of the spectrum analyzer. The RF signal fi nally reached the spectrum analyzer inside the van through a third coaxial pigtail. Due to the high loss of the The switches of the front-end up to 18 GHz are selectable spiral coaxial cable above 6 GHz, a Mini Circuits amplifi er through a remote controller that is located inside the van. This (model ZVA-183+) was placed at the input connector of the device also allows supplying power to the amplifi ers placed on spectrum analyzer to reduce its noise contribution in channels the top of the mast. E and F. A block diagram of the receiving system with all the devices used for channels A, B, and C is shown in Figure 4. The software interface was implemented to save the Figure 3. The inner part of the mobile laboratory. The main spectra, either in tabular form or as a plot in the computer, for workspace shown in the picture consists of two seats, one The RF system was accurately characterized by using further data processing. In the same computer, the cartography to operate the RF instrumentation and the other for the microwave instrumentation. For each frequency channel, the is run to fi nd the direction from where the interference comes. computer. gain and the noise fi gure of the whole RF chain, measured without considering the antennas but including the spectrum analyzer, are reported in Table 2. Another fundamental parameter to be considered was the 1 dB compression point, modifi cations – mainly to the RF cable connecting the top and to avoid any nonlinearity of the receiving system. This ranged bottom of the mast – it could be extended up to 40 GHz. approximately between +6 and +25 dBm, depending on the frequency at the input of the spectrum analyzer. The mobile station is self-powered by the van alternator and auxiliary batteries, in connection with inverters, to provide The outer spiral cable loss was −23.4 dB at 18 GHz. A both 12/24 V dc and sinusoidal 220 V ac at 50 Hz. A few safety radically different confi guration therefore had to be used to Figure 4. A schematic of the receiver chain with the log- interlocks disable the engine’s ignition under unsafe conditions, cover the frequency range above 18 GHz. In this setup, a low- periodic dipole array. This confi guration is valid for for example, when the telescoping mast or the leveling jacks are loss coaxial cable (Gore Phasefl ex type 0K) was used in a loose channels A, B, and C. not correctly parked. confi guration in place of the standard spiral cable. The cable was made 7 m long as a tradeoff between signal loss and the ranged between 11 dB at 18 GHz to 17 dB at 40 GHz. An Driving navigation and radio triangulations are assisted maximum height of the antenna above the ground. Cable loss by a cartography GPS system connected to a computer. Radio automatic stop of the telescoping pole was set at 8 m to prevent paths and approaching roads can then be easily selected in the breaking the cable. In this confi guration, the front-end box was most intuitive graphical form. replaced by a single amplifi er (Miteq JS42-18004000-35-5P) Table 1. The antennas available in the mobile laboratory. placed between the horn and the Gore cable. A further robust amplifi er (Miteq JS3-18004000-50-15P) found a place after the Frequency Frequency Gain in cable to reduce the noise contribution of the spectrum analyzer. Type Coverage 3. Microwave Front Ends and Antennas Bands Band [dBi] Neither pigtails nor transitions were used in this confi guration [GHz] to limit the signal loss, which would add a noise contribution. In order to cover the full frequency range from 300 MHz P band LPDA 0.29 – 0.45 11 – 12 For this frequency band, the total gain ranged from 60 to 70 dB, up to 40 GHz, four commercial antennas were selected: they L/S band LPDA 1.2 – 3.3 11 – 11.5 whereas the noise fi gure was approximately 3.5 dB. In this case, were single polarized, either log-periodic dipole arrays (LPDA) the 1 dB compression point turned out to be +17 dBm at the C/X/Ku band Dual-ridge horn 1 – 18a 6 – 16 or dual-ridged horns, with characteristics as in Table 1. The input of the spectrum analyzer. K/Ka band Dual-ridge horn 18 – 40 18 – 24 antennas can be placed, one by one, over the polarizer on the Figure 5. The RFI mobile laboratory in the foreground, top of the telescope mast. The most stringent requirements in aActually, this antenna is used in the frequency range from 3 GHz to 18 GHz, A complete technical description of the RF receiving and the Sardinia Radio Telescope pointing in the zenith terms of weight and size concerned the log-periodic dipole where the gain is between 10 dBi and 16 dBi. system, along with its characterization, was reported in [7]. direction in the background (Gianni Alvito, INAF-OAC).

IEEE Antennas and Propagation Magazine, Vol. 55, No. 5, October 2013 23

AP_Mag_Oct_2013_Final.indd 23 12/15/2013 3:53:15 PM 5. Examples of Two RFI Campaigns this will offer an opportunity for scientists to integrate over larger bandwidths than the bandwidth allocated to the radio- Postscript: Besides the routine campaigns to monitor the spectrum astronomical service. around the Sardinia Radio Telescope’s area, the mobile The Inauguration of the laboratory has recently been involved in supporting the Italian This preliminary survey was also useful during the telecommunication authority in identifying an interference commissioning phase of a new receiver to be installed at the disturbing an ESA (European Space Agency) mission. Their radio telescope. Information on the RFI environment is crucial Sardinia Radio Telescope Soil Moisture and Ocean Salinity (SMOS) satellite [8], fl ying when it is needed to distinguish the external radio-frequency above South Sardinia, detected an interfering signal in the interferers from self-interference signals originating within the receiving chain, or from any other radiating electronic device ith a big ceremony, the Sardinia Radio Telescope (SRT) Giovanni Bignami, who also read a message from the President passive 1400 MH to 1427 MHz band (which is protected by was inaugurated on September 30, 2013 (Figure 1). of the Italian Republic, Giorgio Napolitano. After the discourses recommendation 5.340 of the ITU Radio Regulations), but located nearby. These two examples show how versatile and W effi cient a mobile laboratory is in detecting radio-frequency The offi cial inauguration was held in the presence ofthe of the invited speakers, the ribbon cutting formally inaugurated without any clue as to its origin. The ESA report to the Italian Parliament Secretary of the Minister of Education, University the radio telescope. In the afternoon, hundreds of people visited administration triggered a formal request to us, through the interfering signals, not only for the radio-astronomy service, but in principle for any other radio service, satellite included. and Research, Marco Rossi Doria, and of the highest local and the equipment rooms of the antenna, guided by the antenna territorial authority, to support their efforts in locating such national authorities (Figure 2). International representatives team. interference. The fi rst guess from the satellite data indicated of the radio-astronomical community joined the event: the the area over the town called Dolianova (latitude 39°22’45”, Director of JIVE, Hub Van Langevelde, and the EVN Chair and The Sardinia Radio Telescope is a general-purpose, fully longitude 09°10’46”). The most suspicious location of the 6. References Radionet coordinator, Anton Zensus. The ceremony was also steerable 64-m diameter parabolic radio telescope, capable interference was focused at the peak of the Serpeddì mountain, open to normal citizens: approximately 2000 people from the of operating with high effi ciency in the 0.3 GHz to 116 GHz 10 km from Dolianova, where a lot of broadcasting and radio- 1. http://pos.sissa.it/cgi-bin/reader/conf.cgi?confi d=107. neighboring municipalities attended the inauguration. frequency range (Figure 3). The Sardinia Radio Telescope is a link antennas are hosted. However, after many measurements fl exible instrument aimed at increasing knowledge in several with the mobile laboratory, it was discovered that the RFI 2. R. Ambrosini, C. Bortolotti, M. Roma, “Sistema di Ricezione The opening welcome was given by the Director of the fi elds: radio astronomy, geodynamical studies, and space was produced from a totally different location: 60 km away, 18-40 GHz per la Ricerca di Interferenze con Laboratorio Sardinia Radio Telescope project, Nichi D’Amico, and by science, either in single-dish or VLBI mode. The project is in the south-southwest direction. The source of the RFI was a Mobile,” Technical Report of the Institute of Radio Astronomy, the President of the Italian Institute for Astrophysics (INAF), the result of a scientifi c and technical collaboration among malfunctioning commercial amplifi er, used as a TV distributor n. 420/08 (in Italian), http://www.ira.inaf.it/Library/rapp- in a residential building, re-radiating back into the sky its self- int/420_08.pdf. oscillation at L band. In this case, the identifi cation of the true location of the interferer was particularly diffi cult due to 3. http://www.med.ira.inaf.it/Interferenze_page_EN.htm. multipath propagation effects in a region with a very irregular vertical profi le. 4. A. Orfei, M. Morsiani, G. Zacchiroli, G. Macaferri, J. Roda, and F. Fiocchi “An Active Surface for Large Refl ector The second example we want to mention referred to a Antennas,” IEEE Antennas and Propagation Magazine, 46, 4, survey performed in October 2011, aimed at verifying the August 2004. RFI distribution in the frequency band 5.7 GHz to 7.7 GHz, accessed by the fi rst receiver that will operate in the Sardinia 5. G. Tofani et al., “Status of the Sardinia Radio Telescope Radio Telescope. Two different locations in the neighborhood Project,” Proceedings of SPIE Conference on Ground-Based of the radio telescope were selected so as to include both a and Airborne Telescopes II, Marseille, France, Vol. 7012, 2008, realistic and a more-pessimistic view of the expected spectrum http://spie.org/x648.html?product_id=790503. receivable by the Sardinia Radio Telescope. The latter was

obtained by taking measurements from the top of a nearby hill, 6. http://www.gbarberi.com/. but with higher altitude than the Sardinia Radio Telescope. As

a matter of fact, this usually compensates for the difference 7. P. Bolli, F. Gaudiomonte, R. Ambrosini, C. Bortolotti, and in sensitivity between the mobile laboratory and the radio M. Roma, “The Receiving System of the Mobile Laboratory telescope. for RFI Measurements” Technical Report of the Astronomical Observatory of Cagliari, n. 20/12 (in Italian), http://www.oa- Even if in this band, only a narrow portion of the cagliari.inaf.it/area.php?page_id=10. spectrum is actually reserved to the radio-astronomical service (6650.00 MHz to 6675.20 MHz, which includes the methanol 8.http://www.esa.int/esaLP/ESAMBA2VMOC_LPsmos_0. line), we discovered that the real active occupancy of this html. band (especially above 6.4 GHz) is quite scarce. Hopefully,

Figure 1. On September 30, 2013, the inaugural ceremony of the Sardinia Radio Telescope took place in the presence of the highest local, national, and international authorities. Additionally, 2000 people from the neighboring municipalities attended the inauguration.

24 IEEE Antennas and Propagation Magazine, Vol. 55, No. 5, October 2013

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