EMI in an RQZ: the need for buffer zones Carol Wilson, CSIRO Research Consultant RFI2010, Groningen

Outline of presentation Introduction – purpose of EMI buffer zone analysis Prediction method components Interference thresholds Emission levels Characterisation of EMI activities Prediction of attenuation Examples of analysis Results of buffer zone analysis Close

Introduction – EMI buffer zones Intentional radio transmitters  narrowband signals  variety of mitigation techniques (including avoidance) Noise from electrical equipment, machinery  broadband interference  harder to mitigate Need to define buffer zones around human activity to avoid EMI in design of SKA array configuration

Challenges due to SKA requirements Frequency – 70 MHz to GHz – large compared to most current telescopes Physical extent of telescope (large number of separate stations over a large geographic extent) Rigorous demands of radioastronomy Time frame (current -> ~2020 -> 50 years or more)

SKA three zone approach Core (2.5 km radius, 50% of array) with highest levels of protection (aim for ITU-R RA continuum). Intermediate (<180 km radius, 25% of array) with protection relaxed by 15 dB from continuum thresholds. Remote (> 180 km, 25% of array) with protection relaxed by further 25 dB (corresponds to VLBI levels). Core site chosen in a remote location Intermediate and remote sites to be chosen based on RFI, UV coverage, geophysics, logistics, etc Buffer zones for separation from EMI needed for intermediate and remote sites

Components of prediction model Emission level – radioastronomy threshold = attenuation required Model expected usage patterns of equipment Use propagation model to find distance at which attenuation is exceeded Thresholds established by ITU-R Study Group 7 Emissions – use published EMC/EMI standards Model of usage patterns - estimated Attenuation – need propagation model(s)

Defining radio quietness ITU Recommendation RA Harmful interference levels assuming reception into 0 dBi sidelobe Values for continuum, spectral line and VLBI observations Continuum observation values used as basic protection levels for SKA core Frequency f (MHz) Assumed bandwidth  f (kHz) Threshold interference levels Input power  P H (dBW) Pfd S H  f (dB(W/m 2 )) Spectral pfd S H (dB(W/(m 2  Hz))) (7)(8)(9) –199 –201 –203 –202 –205 –207 –202 –195 –194 –189 –185 –180 –181 –177 –171 –160 –156 –146 –147 –259 –258 –255 –253 –255 –251 –247 –241 –240 –233 –231 –233 (7) Power level at the input of the receiver considered harmful to high sensitivity observations,  P H. This is expressed as the interference level which introduces an error of not more than 10% in the measurement of  P. (8) pfd in a spectral line channel needed to produce a power level of  P H in the receiving system with an isotropic receiving antenna. (9) Spectral pfd needed to produce a power level  P H in the receiving system with an isotropic receiving antenna.

Interference thresholds

Emission standards Interference power as a function of frequency from: Road vehicles – CISPR standard 12:2005. Railways – European EN : Household appliances and tools – CISPR standard 14- 1:2003. Arc welders – CISPR standard 11:2004. Power lines - Australian standard AS/NZS 2344:1997. Frequency dependence: Roads: increasing to 400 MHz, then constant Rail: decreasing with frequency Appliances/tools: increasing to 300 MHz, assumed constant beyond

Categories Farmsteads/individual dwellings = 7 appliances, 4 power tools and 1 vehicle. Towns – n x dwellings, assumption that 1/3 of households are “active” at any time. Roads – minor (small number of vehicles per day) and major (multiple vehicles for a substantial part of the day) Rail – lightly used (4 trains a day) and heavy (continuous use) Mines – based on town analysis for similar activity Power lines – range of voltages

Propagation models Some propagation models use specific terrain For buffer zones, generic models needed ITU-R Recommendation P used for EMI buffers Inputs: frequency, terminal heights, time percentage, type of path (land, sea, mixed) Interference source height: 2 metres (except power lines) Telescope height: 1 metre 300 MHz Model used iteratively to find distance for required loss Attenuation increases as function of frequency Attenuation decreases with higher antenna heights (discontinuity at 300 MHz due to telescope height)

Example – minor roads At 300 MHz, vehicle emission level = 63 (dBμV/m) = dBW/Hz At 300 MHz, the RA threshold = -258 dB(W/m 2 ·Hz). Intermediate zone, relaxed by 15 dB, = -243 dB(W/m 2 ·Hz) = -269 dBW/Hz The attenuation required = -269 – (-102.5) = dB For antenna heights 15 m (telescope) and 2 m (interferer), at 300 MHz, distance = 12 km Furthermore…

Example – minor roads (continued) Allow 10 vehicles per day within 12 km for 5% of day. 0.05*24*60 = 72 minutes or 7.2 minutes per vehicle At 100 km/hr, vehicle travels 12 km in 7.2 minutes Relax limit to 10.5 km as shown Repeat at other frequencies 12 km 10.5 km 12 km

Example – minor roads (continued)

Example for remote zone (25 dB relaxation)

Buffer zones for intermediate and remote stations IntermediateRemote Minor roads10.5 km3 km Major roads Local rail Heavy rail Farms13.53 Towns: 100 people people people people Power linesUp to 8 kmUp to 1.5 km

Conclusions Core of SKA to be protected primarily by remote location Buffer zones around human activity have been defined for the intermediate and remote stations of the SKA The methodology for calculation can be applied to other scenarios (e.g. intermediate traffic roads) EMI buffer zones will be part of analysis in optimising the SKA array configuration

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