Living with radio interference (rfi) Define Interference Please

Transcription

1 Living with radio interference (rfi) Define Interference Please VDE 0875/71 (Verband der Elektrotechnik Elektronik Informationstechnik) CISPR 22 (Comité International Spécial des Perturbations Radioélectriques) ISO 11451* (International Organization for Standardization) FCC part 15 (Federal Communications Commission) MIL-STD 461 (US military standard) IEC EN * (International Electrotechnical Commission) EN (European Norm) Christian Monstein, Institute for Astronomy, ETH Zurich, Switzerland RAS meeting, London

2 Radio Astronomy, a Passive Service Among Active Users 1 s integration time, BW ~ 60 KHz, telescope pointing to the sky

3 RFI and population density Montevideo Uruguay Pop. 1.4 million Bleien, Switzerland Pop Gold mine Castrillon, Minas de Corrales, Uruguay Pop (2012)

4 Radio Frequency Interference Operational conditions of RAS define at what level RFI is damaging detrimental harmful ITU-R RA defines detrimental as 10% of system noise power using a reference time interval of 2000 sec and Tsys & bandwidth and 0 dbi entry for each RAS band Such a signal is still buried in the noise of a single observation but will show up after smoothing and in longer integration Define data loss due to RFI as loss of part or all of the band or part or all of the time data loss requires re-observation or total loss in timecritical observations

5 Defining Radio Quietness ITU Recommendation RA Harmful interference levels assuming reception into 0 dbi sidelobe Values for continuum, spectral line and VLBI observations Frequency f (MHz) Assumed bandwidth D f (khz) Input power DP H (dbw) Threshold interference levels Pfd S H D f (db(w/m 2 )) Spectral pfd S H (db(w/(m 2 Hz))) (7) (8) (9) BINGO (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.

6 Threshold levels ITU-R RA Interference threshold levels from Recommendation ITU-R RA Spectral pfd (db(w/(m2 Hz))) Tx with 1 mw EIRP in 50 khz on the Moon Frequency (MHz) Continuum Continuum +15 Line VLBI BAO < 10 nw on the Moon

7 Radiation limits for electronic devices commercial residential To be on the save side take into account maximum electrical field strength of 50 dbμv/m for any electronic device. Different national and international committees have different opinions about maximum radiation level (CISPR-22, EN55011, FCC part 15, VDE,..) At least FCC defines radiation also above 1 GHz.

8 Calculations Maximum electric field strength at r = 10 m (FCC) = 50 db [µv/m] = µv/m Maximum power flux density P fd = మ = మ ଵଶగஐ = pw/m2 Peak power of rfi-source P max = P fd 4π r 2 = nw Minimum distance D min in case of free space loss: ௫ ସ ௐ S min according to ITU 100 Jy but much less for BINGO 1 mjy BW = 50 KHz for spectral and 300 MHz for continuum observation Minimum distance D min in case of free space ITU-769: -240 db(w/m 2 /Hz) ~ 100 Jy BINGO: -290 db(w/m 2 /Hz) ~ 1 mjy Spectral BW = 50 KHz 728 km km (61% Moon) Continuum BW = 300 MHz 53 km km

9 RFI examples Damage to RAS observations depends on type of experiment Continuum obs. & narrow-band rfi less damaging Continuum obs. & broad-band rfi very damaging spectral line obs. & narrow-band rfi => depends where Spectral line obs. & broad-band rfi => very damaging

10 How to measure RFI? Automatic dependent surveillance-broadcast (ADS-B) at 1090 MHz Secondary surveillance radar (SSR) at 1130 MHz

11 Measurement hardware at ETH Zurich

12 How to deal with RFI? Excision (flagging) or software removal of RFI Additional RFI mitigation possible at RAS station to further reduce manmade signals (in-house and external) Engineering solutions (filters, receivers, coordination distances) All mitigation of RFI in the data leads to Data Loss and lower quality of data Prevention always better than mitigation, e.g. - no webcams within a few km - no electronic environmental sensors close to telescope - no electric motors, no petrol engines using spark plugs, - no electrical fences, no cows with RFI-tags - no mobile phones, no wireless applications - no windmills, no photo-voltaic installations - no electrical devices at all.

13 How to deal with RFI? Blue: background while windmill is off, red: rfi while windmill is operating

14 Bleien observatory rfi-map with beam ~4 Day observation 12:36-17:18 excluding satellites

15 Bleien observatory rfi-map with beam ~4 Day observation 12:36-17:18 including satellites