Electromagnetic Compatibilityin Radio Astronomy
Harshit Srivastava Rahul Sinha
1
ext.
s EMC.
Content
What is EMC?Motivation EMC in the radio astronomy context
Optimization components Towards EMC
Electromagnetic Compatibility in Radio Astronomy2
Problem: Electro Magnetic Compatibility EMC
"The goal of EMC is the correct operation, in the sameelectromagnetic environment, of different equipment which
useelectromagnetic phenomena, and the avoidance of anyinterference effects. .“ (Source: Wikipedia)
Regulations for
Industry products:EN55011VDE 0878-1
Radioastronomy: ITU- R RA 769-2
Source: left: Dr. Hj. Biener / right: RP online
Electromagnetic Compatibility in Radio Astronomy3
Radio Interference in Radio Astronomy
(Jim Cohen, 2005)
external:TV, Radar, Satellites, aircraftData Processing, Electronics
internal:oscillations, intermods, harmonics, receiver noise
Radio interference is a radio signal of human origin which is detected in a radio astronomical observation
EMC of PV Components at FhG/ISE
Untersuchung der elektromagnetischen Eigenschaften des Solar- generators in netzgekoppelten photovoltaischen Stromversorgungs- anlagen, BMBF 1994 – 1997
Development of standard testprocedures for electromagnetic interference tests and evaluations on photovoltaic components and plants, EC, 1998 – 2000
Green:Blue:
Red:
Noise floorunmodified power inverter
EMC optimized power inverterSource: FhG/ISE
Electromagnetic Compatibility in Radio Astronomy5
EMC policy
EMC compliance by filtering
Source: FhG/ISE
Electromagnetic Compatibility in Radio AstronomyMoura, June 20, 2012 6
Motivation
Max-Planck-Institut for Radioastronomy & EMC
Long (and bad) experience with Radio Frequency Interference
Measurement equipment and experience for RFI
Extremely sensitive astronomical instruments
Telescopes as test beds for EMC
measurements
(RFI)
Electromagnetic compatibility of all SKA equipment
Electromagnetic Compatibility in Radio Astronomy7
Performance Requirements of Radioastronomy
I.E.: Mobile phone on the moon* Distance abt. 400.000 km* Power 2 Watt
→ one of the strongest radio sourcesthe sky for the 100m radio telescopeEffelsberg
at
Electromagnetic Compatibility in Radio Astronomy8
Signal / Noise
Interferer
Astronomy Signal (Spectral lines)
Electromagnetic Compatibility in Radio Astronomy9
From IRIDIUM Satellite 1500 km distance:7th order intermod product: e.i.r.p. 1mWMain carrier: e.i.r.p. 12.5 W
Electromagn
∆S ≈ − 40
dBN
How is it done ?
∆S
The sensitivity is theprecision of a noisepower measurement.
2 ⋅ k ⋅ Tsys 1∆S ν =
ε ant A ant ∆ν ⋅ t int
It can be much smallerthan the system noiseitself!
independent power
Largeantennasd=100m
Cryogenicreceivers
etic Compatibility in Radio Astronomy10
N samples = number of
measurements
Typical radio astronomical signals (‚cosmic noise‘) are detected as an addition to receiver and sky noise power
Antenna Gain is different for Astronomy and for RFI
Main beamEffelsberg 21cm:
0.54. π . ( 50. m)2 =
4.241 103
2m
η. AA eff geoG beam A isotropic antenna:
( 21. cm)2iso
4.π 3 2= 3.509 10 mX , Y , Z
4. π
= 1.209 106 10. log G dBi= 60.823G beambeam
1°<φ<47.8°47.8 <φ<180°
Off-beam gain:ITU-R S. 1428
G=32-25log (φ) dBi forG= -10 dBi for
Electromagnetic Compatibility in Radio Astronomy11
Average Antenna gain for RFI is Grfi ~ 1 or 0 dBi (isotropic antenna)
λ2
Radio Regulations:Detrimental thresholds for total power observations
180
requencies > 30 MH are importantITU-R RA 769
200
I/N =0.1 220
240
2 1 Jy0.4πkf (TA +TR ) 260
S H
=2 ∆
fτc 3
1 .100.01 0.1 1 10 100(Thompson,2005)
Frequency GHz
black, continuum; red, spectral lineRA Handbook Fig. 4.1 (p. 36)
Signal averaged over τ = 2000 sand bandwidths of several MHz
Electromagnetic Compatibility in Radio Astronomy12
SP
FD
[dB
W /(
m^2
.Hz)
]
Thresholds are defined for the location of the radio telescope !
fr z e i
Radiated Emission Limits for Industrial Devices
CISPR-11 Group 1 Class AEN 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!
Spectrum occupation undefined!
Electromagnetic Compatibility in Radio Astronomy13
Limits defined for the interfererer !
Industrial Equipment Interference and Radio Astronomy
Emission and Reception Power Limits50 The ITU report SM-1081 describes
A. Protection requirements of radio astronomy as inITU-R RA. 769,limits for industrial equipment as given by CISPR-
11. (EN 550011)
100
140 dB B.150
200
Separation Distances for ISM Equipment100
2503 4 510 100 1 10 1 10 1 10
frequency (MHz)
10
13 4 510 100 1 10 1 10 1 10
frequency (MHz)
The standards set for ISM equipment need to be made consistent with those of the ITU-R RA. 769 forthe bands listed in footnotes 5.340 and 5.149 of the RR .
Electromagnetic Compatibility in Radio Astronomy14
dB(W
)
dist
ance
(km
)
A very difficult task as it concerns all manufactured equipment:From cattle fences over digital electronics to wind power generators!
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!
1
RFI in Radioastronomy
Electromagnetic Compatibility in Radio Astronomy15
r‘Pulsed Radio Sources ‚Pulsa
T = 1,4sec
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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 maximumside-lobe gain Gmax(f) = 32 - 25log(fmin). If the antenna can point at thestructure, 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 fromdevices 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 designrequirement. High frequencies (> 1 GHz) and spectrum coverage must be taken into account.
Electromagnetic Compatibility in Radio Astronomy17
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
125 140 155 170 185 200 dB
Required minimum path loss
Electromagnetic Compatibility in Radio AstronomyMoura, June 20, 2012 18
Emission limit in blue region:>>20 dB below CISPR-11
Radiation with shielding and filtering TV channels!
EMC of a Solar Lamp
Radiation of the shelf
Electromagnetic Compatibility in Radio Astronomy19
Ethernet Media Converter 100BaseT / Optical fibre
Strong interferers, i.e. 650MHz blue line
In house shielding case with EMC filters green line
Electromagnetic Compatibility in Radio Astronomy20
Given and Acceptable Radio Emissions
60
EMC policy
40PV-Plant
lam
20
0Radio astronom
guideline
Media converter20
403 4 510 100 1 10 1 10 1 10
Frequency in MHz
Electromagnetic Compatibility in Radio Astronomy21
El.
Fie
ldst
ren
gth
in d
Bµ
V/m
polic
P
So
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Radi g
y
co
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
Verify by sensitive measurements!
EMC measures are required
Electromagnetic Compatibility in Radio Astronomy22
Conclusion
We have: Expertise in EMC theory and measurement techniques,
EMC-test bed (100m, LOFAR, ASKAP)
Leadership in RFI mitigation
Strong partners
for monitoring
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 Astronomy23
Thank you for your attention!
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