Published on February 14, 2014
Electromagnetic Compatibility in Radio Astronomy Harshit Srivastava Rahul Sinha 1
Content What is EMC? Motivation EMC in the radio astronomy context ext. s EMC Optimization components Towards EMC. Electromagnetic Compatibility in Radio Astronomy 2
Problem: Electro Magnetic Compatibility EMC "The goal of EMC is the correct operation, in the same electromagnetic environment, of different equipment which use electromagnetic phenomena, and the avoidance of any interference effects. .“ (Source: Wikipedia) Regulations for Industry products: EN55011 VDE 0878-1 Radioastronomy: ITU- R RA 769-2 Source: left: Dr. Hj. Biener / right: RP online Electromagnetic Compatibility in Radio Astronomy 3
Radio Interference in Radio Astronomy Radio interference is a radio signal of human origin which is detected in a radio astronomical observation (Jim Cohen, 2005) external: TV, Radar, Satellites, aircraft Data Processing, Electronics internal: oscillations, intermods, harmonics, receiver noise
EMC of PV Components at FhG/ISE Untersuchung der elektromagnetischen Eigenschaften des Solargenerators in netzgekoppelten photovoltaischen Stromversorgungsanlagen, BMBF 1994 – 1997 Development of standard test procedures for electromagnetic interference tests and evaluations on photovoltaic components and plants, EC, 1998 – 2000 Green: Noise floor Blue: unmodified power inverter Red: EMC optimized power inverter Electromagnetic Compatibility in Radio Astronomy 5 Source: FhG/ISE
EMC policy EMC compliance by filtering Source: FhG/ISE Electromagnetic Compatibility in Radio Astronomy Moura, June 20, 2012 6
Motivation Max-Planck-Institut for Radioastronomy & EMC Long (and bad) experience with Radio Frequency Interference (RFI) Measurement equipment and experience for RFI Extremely sensitive astronomical instruments T elescopes as test beds for EMC measurements Electromagnetic compatibility of all SKA equipment Electromagnetic Compatibility in Radio Astronomy 7
Performance Requirements of Radioastronomy I.E.: Mobile phone on the moon * Distance abt. 400.000 km * Power 2 Watt → one of the strongest radio sources at the sky for the 100m radio telescope Effelsberg Electromagnetic Compatibility in Radio Astronomy 8
Signal / Noise From IRIDIUM Satellite 1500 km distance: 7th order intermod product: e.i.r.p. 1mW Main carrier: e.i.r.p. 12.5 W Interferer Astronomy Signal (Spectral lines) Electromagnetic Compatibility in Radio Astronomy 9
How is it done ? Typical radio astronomical signals (‚cosmic noise‘) are detected as an addition to receiver and sky noise power The sensitivity is the precision of a noise power measurement. ∆S ν = It can be much smaller than the system noise itself! 2 ⋅ k ⋅ Tsys 1 ε ant A ant ∆S ∆ν ⋅ t int N samples = number of independent power measurements Large antennas d=100m ∆S ≈ − 40 dBN Electromagnetic Compatibility in Radio Astronomy 10 Cryogenic receivers
Antenna Gain is different for Astronomy and for RFI Main beam Effelsberg 21cm: 0.54. π . ( 50. m) 2 = 4.241 G beam 103 A eff η. A geo A iso λ2 4. π isotropic antenna: (21. cm) X ,Y , Z 4. π 6 G beam = 1.209 10 Off-beam gain: ITU-R S. 1428 2 m 2 = 3.509 10 3 2 m 10. log G beam = 60.823 dBi G=32-25log (φ) dBi for 1 <φ<47.8 G= -10 dBi for 47.8 <φ<180 Average Antenna gain for RFI is Grfi ~ 1 or 0 dBi (isotropic antenna) Electromagnetic Compatibility in Radio Astronomy 11
Radio Regulations: Detrimental thresholds for total power observations 180 fr ei requencies > 30 MH z are important ITU-R RA 769 I/N =0.1 SPFD [dBW /(m^2.Hz)] 200 220 240 0.4πkf (TA + TR ) SH = c 2 ∆ fτ 1 Jy 2 260 0.01 Signal averaged over τ = 2000 s and bandwidths of several MHz 0.1 1 10 100 3 1 .10 (Thompson,2005) Frequency GHz black, continuum; red, spectral line RA Handbook Fig. 4.1 (p. 36) Thresholds are defined for the location of the radio telescope ! Electromagnetic Compatibility in Radio Astronomy 12
Radiated Emission Limits for Industrial Devices CISPR-11 Group 1 Class A EN 61800-3, Cat. 4 : I>400 A or U > 1000 V • for frequencies below 230 MHz : 30 dBµV/m, 120 kHz measurement bandwidth • for frequencies above 230 MHz: 37 dBµV/m, 1 MHz Measurement bandwidth Distance = 10m, with quasi-peak detector • for frequencies above 1 GHz: not defined for all types of equipment! Limits defined for the interfererer ! Spectrum occupation undefined! Electromagnetic Compatibility in Radio Astronomy 13
Industrial Equipment Interference and Radio Astronomy Emission and Reception Power Limits 50 The ITU report SM-1081 describes A. Protection requirements of radio astronomy as in ITU-R RA. 769, B. limits for industrial equipment as given by CISPR-11. (EN 550011) 140 dB 1 150 200 Separation Distances for ISM Equipment 250 10 100 100 3 1 10 frequency (MHz) 4 1 10 Industrial equipment emissions on the level of these limits require free-space separation distances of several 10 km from telescopes in order to fulfil the ITU-R RA. 769 protection requirements! 5 1 10 distance (km) dB(W) 100 10 1 10 100 3 1 10 frequency (MHz) 4 1 10 The standards set for ISM equipment need to be made consistent with those of the ITU-R RA. 769 for the bands listed in footnotes 5.340 and 5.149 of the RR . A very difficult task as it concerns all manufactured equipment: From cattle fences over digital electronics to wind power generators! Electromagnetic Compatibility in Radio Astronomy 14 5 1 10
RFI in Radioastronomy Electromagnetic Compatibility in Radio Astronomy 15
Pulsed Radio Sources ‚Pulsar‘ T = 1,4sec Electromagnetic Compatibility in Radio Astronomy 16
Generic Case: Impact assessment procedure 1. Calculate the effective path loss Lb(f) from the telescope to the site for each frequency band using the methods of ITU-R P .452-12. 2. If the antenna cannot point at the structure, then calculate the maximum side-lobe gain Gmax(f) = 32 - 25log(fmin). If the antenna can point at the structure, then use the full main beam gain of the antenna. 3. ITU-R RA. 769 gives a table of reception limits of continuum input power ∆PH (table 1, column 7) for each radio astronomical frequency. Any emission from devices at the planning site must be kept below the limit of ∆Psite= ∆PH+ Lb(f) - Gmax(f) -10 log(Ndev) (The effect is additive for Ndev similar devices at the same site) 4. Repeat for all relevant frequencies to estimate site emission limits 5. Their difference to actual emissions is the additional EMC design requirement. High frequencies (> 1 GHz) and spectrum coverage must be taken into account. Electromagnetic Compatibility in Radio Astronomy 17
Attenuation Map for 610 MHz at a SKA Remote Site Calculated with ‚Pathprofile‘ (M. Willis) Height of emission 5 m Antenna height 10 m 30 km Emission limit in blue region: >>20 dB below CISPR-11 125 140 155 170 185 Required minimum path loss Electromagnetic Compatibility in Radio Astronomy Moura, June 20, 2012 18 200 dB
EMC of a Solar Lamp Radiation of the shelf Radiation with shielding and filtering TV channels! Electromagnetic Compatibility in Radio Astronomy 19
Ethernet Media Converter 100BaseT / Optical fibre Strong interferers, i.e. 650MHz In house shielding case with EMC filters blue line green line Electromagnetic Compatibility in Radio Astronomy 20
Given and Acceptable Radio Emissions 60 El. Fieldstrength in dBµV/m polic EMC policy 40 PV-Plant P Solar lamp la 20 0 Radi Radio astronom y g guideline co Media converter 20 40 10 100 3 1 10 Frequency in MHz Electromagnetic Compatibility in Radio Astronomy 21 4 1 10 5 1 10
Summary • EMC with Radio Astronomy is a serious problem. • Frequencies above 30 MHz are important • Interferer (CISPR) and victim (ITU-R RA 769) standards are not harmonised • For compatibility assessments, the emissions from the interferer and their spectral characteristics must be well known (better than CISPR). • Spatial separation of a few km is insufficient on its own: minimum coupling losses (MCL) > 135 dB • Case by case compatibility analysis and taylored EMC measures are required • Verify by sensitive measurements! Electromagnetic Compatibility in Radio Astronomy 22
Conclusion We have: Expertise in EMC theory and measurement techniques, EMC-test bed (100m, LOFAR, ASKAP) for monitoring Leadership in RFI mitigation Strong partners We need: Extremely sensitive telescope in a RFI free environment remote and without infrastructure Independant and affordable energy EMC Components for power supply. Electromagnetic Compatibility in Radio Astronomy 23
Thank you for your attention! Electromagnetic Compatibility in Radio Astronomy 24
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