RFI at GMRT: Detection, Suppression and Co-existence Pravin Raybole, S.Sureshkumar GMRT, India Pravin Raybole, S.Sureshkumar GMRT, India.

RFI at GMRT: RFI at GMRT: Detection, Suppression and Co-Detection, Suppression and Co-

existence existence Pravin Raybole, S.Sureshkumar GMRT, Pravin Raybole, S.Sureshkumar GMRT,

IndiaIndia

AcknowledgementAcknowledgement Yashwant Gupta, GMRT Chief ScientistYashwant Gupta, GMRT Chief Scientist A. Praveen KumarA. Praveen Kumar S. Suresh KumarS. Suresh Kumar B. Ajith KumarB. Ajith Kumar Suresh SabhapathySuresh Sabhapathy M. R. SankararamanM. R. Sankararaman

Field Team membersField Team members Amit Sawant, Manoj Chavan, Rahul Durgude, Amit Sawant, Manoj Chavan, Rahul Durgude,

Dhairyashil Dhamdere, Mukund Deshmukh, Milind Dhairyashil Dhamdere, Mukund Deshmukh, Milind Thorat and Suresh KaleThorat and Suresh Kale

ContentsContents

Introduction to GMRTIntroduction to GMRT RFI Environment at GMRTRFI Environment at GMRT Interference from TV boostersInterference from TV boosters Interference from Cell Phone towersInterference from Cell Phone towers Power line interferencePower line interference RFI detection using the GMRT RFI detection using the GMRT

Software BackendSoftware Backend

The GMRTThe GMRT• GMRT is designed and

built by NCRA – TIFR Pune. Located 80 km N of Pune and 160 km E of Mumbai.

• 30 antennas of 45 meter diameter covering 50MHz to 1450 MHz

• 12 dishes in central compact (1km) array

• Remaining along 3 arms of Y-array, longest baseline (25kms)

14 km

1 km x 1 km

SW FM

TV

SA

TE

LL

ITE

PO

LIC

E

WIR

EL

ES

S

RF Spectrum at GMRT : 0 – 500 MHz

AT

C

Day 12:00 hours

Night 22:00 hours

TV

CDMA

GSM

RF Spectrum at the GMRT : 500MHz – 1GHzDay 12:00 hours

Night 22:00 hours

RF Spectrum at the GMRT : 1GHz – 2GHz

GSM

Day 12:00 hoursNight 22:00 hours

GMRT : Operating Frequency BandsGMRT : Operating Frequency Bands

FrequencyFrequency Radio Astronomy Radio Astronomy Band Band

System System BandwidthBandwidth

Source of Interference Source of Interference observed near Radio observed near Radio

Astronomy band.Astronomy band.

150 MHz150 MHz 150 – 153.6 MHz150 – 153.6 MHz 130 – 230 MHz130 – 230 MHz Air Traffic control, Fixed Mobile, Air Traffic control, Fixed Mobile, TV Transmission, TV Transmission,

235 MHz235 MHz 230 – 235 MHz230 – 235 MHz 213 – 253 MHz213 – 253 MHz

Planned:Planned:

250 – 500 250 – 500 MHzMHz

Digital Audio Broadcast ( DAB ), Digital Audio Broadcast ( DAB ), Aeronautical Radio Navigation, Aeronautical Radio Navigation, Leakage from Cable TV signals.Leakage from Cable TV signals.

327 MHz327 MHz 322 – 328.6 MHz322 – 328.6 MHz 295 – 365 MHz295 – 365 MHz Fixed Mobile, Aeronautical Fixed Mobile, Aeronautical Radio NavigationRadio Navigation

610 MHz610 MHz 604 – 616 MHz604 – 616 MHz 570 – 660 MHz570 – 660 MHz

PlannedPlanned

550 – 900 550 – 900 MHzMHz

TV TransmissionTV Transmission

1060 – 1060 – 1420 MHz1420 MHz

1400 - 14271400 - 1427 885 – 1450 MHz885 – 1450 MHz Fixed Mobile Broadcasting, Fixed Mobile Broadcasting, SatelliteSatellite

RFI environment at GMRTRFI environment at GMRT

Intentional RadiationIntentional Radiation Unintentional Unintentional RadiationRadiation

TV and FMTV and FM Power Line RFIPower Line RFI

Police Wireless Police Wireless CommunicationCommunication

TV BoostersTV Boosters

Air Traffic ControlAir Traffic Control IndustriesIndustries

Mobile CommunicationMobile Communication Electronics Instruments, Electronics Instruments, Computers Computers

Air ForceAir Force Networking DevicesNetworking Devices

Monitoring the RFI environment at the Monitoring the RFI environment at the GMRTGMRT

Regular monitoring of the RF spectrum.Regular monitoring of the RF spectrum.

Regular field survey to check radiation from Regular field survey to check radiation from new installations.new installations.

Close contact and a shared knowledge base Close contact and a shared knowledge base with government agencies, local industries, with government agencies, local industries, cellular phone operators, electric companies cellular phone operators, electric companies and individuals. and individuals.

Regular studies of internal ( i.e. self Regular studies of internal ( i.e. self generated ) RFI, e.g. from GMRT computers, generated ) RFI, e.g. from GMRT computers, instrumentsinstruments. .

Important RFI sources at the Important RFI sources at the GMRTGMRT

SourcesSources Nature of RFINature of RFI

TV BoostersTV Boosters Broad-band, Broad-band, Narrow band or Narrow band or very narrow linesvery narrow lines

Cellular phones Cellular phones Narrow-bandNarrow-band

Power linesPower lines Broad-bandBroad-band

Interference from TV boostersInterference from TV boosters

Locating TV Booster Locating TV Booster Did a field survey of TV dipole antennas.Did a field survey of TV dipole antennas. Visited every location for RFI measurement. Visited every location for RFI measurement.

• Measurement setup • Log periodic antenna• Spectrum analyzer• 20dB Amplifier• Generator for backup.

Frequency Frequency Range Range

VHF and UHF bandVHF and UHF band

GainGain 40 – 60dB 40 – 60dB

No of stagesNo of stages 2 – 3 cascaded 2 – 3 cascaded stagestage

RFI from TV Boosters : Broad-band

Frequency 40MHz to 650MHz

RFI from TV Boosters : Broad-band

Frequency 314MHz to 375MHz

RFI from TV Boosters : Narrow-band

Frequency 40MHz to 650MHz

Method adopted Method adopted

Before Putting Resistor After Putting ResistorVariable Pot

A 25 paise solution

Problem : Saturation and oscillation of TV booster amplifiersProblem : Saturation and oscillation of TV booster amplifiers

Solution : New resistor added in series with existing variable resistor

Resistance Values : 900 Ohm to 1.2KOhmResistance Values : 900 Ohm to 1.2KOhm

Corrected TV booster Frequency 40MHz to 650MHz

FM TV SIGNAL

Broadband RFI from TV Broadband RFI from TV boostersboosters

Field survey of 25 nearby villages in and around Field survey of 25 nearby villages in and around GMRT with the help of the local administration.GMRT with the help of the local administration.

Inspected nearly 1800 TV boosters over a 3 years Inspected nearly 1800 TV boosters over a 3 years period.period.

Reduced the gain of the amplifier to prevent Reduced the gain of the amplifier to prevent saturation and oscillation, thereby ensuring good saturation and oscillation, thereby ensuring good signal reception.signal reception.

Follow-up monitoring studies found no cases of Follow-up monitoring studies found no cases of recurring problem over a 3-year period.recurring problem over a 3-year period.

Recent field surveys have found that 66% of users Recent field surveys have found that 66% of users have switched to Direct-to-Home services which have switched to Direct-to-Home services which have Ku–band downlink frequencies. These do not have Ku–band downlink frequencies. These do not produce any RFI at GMRT frequencies. The produce any RFI at GMRT frequencies. The situation is likely to continue to improve over the situation is likely to continue to improve over the next year.next year.

Interference from Cellular Interference from Cellular Phone Phone towerstowers

Co-existing with cellular Co-existing with cellular operatorsoperators

Cell phone towers use CDMA (824-896 MHz), Cell phone towers use CDMA (824-896 MHz), GSM (935-960 MHz) and (1811-1880 MHz) and GSM (935-960 MHz) and (1811-1880 MHz) and they operate with 20 Watt and 40 W transmitters.they operate with 20 Watt and 40 W transmitters.

After detail discussions, most of the GSM After detail discussions, most of the GSM operators within a radius of 20 km of GMRT, operators within a radius of 20 km of GMRT, agreed to shift GSM transmissions to the 1800 agreed to shift GSM transmissions to the 1800 MHz band, which does not affect GMRT MHz band, which does not affect GMRT observations. A few towers beyond 20 km have also observations. A few towers beyond 20 km have also been asked to change to 1800 MHz GSM band.been asked to change to 1800 MHz GSM band.

CDMA operators operating at 824-896 MHz are CDMA operators operating at 824-896 MHz are still a serious source of RFI for the GMRT still a serious source of RFI for the GMRT especially with the planned extensions in especially with the planned extensions in frequency coverage. At present, the CDMA frequency coverage. At present, the CDMA operator have been request to use low power operator have been request to use low power transmitters and to focus their transmitters away transmitters and to focus their transmitters away from GMRT antennas. Longer-term solutions are from GMRT antennas. Longer-term solutions are now being examined. now being examined.

GSM transmission at 950 MHz band shifted GSM transmission at 950 MHz band shifted to 1800 MHzto 1800 MHz

NARAYANGAON IDEA RTT 25mtr. TOWER(ABOVE RAJGURUNAGAR BANK) GAMA SECTOR 950MHz BAND TOWARDS HIGHWAY DIRECTION(16-02-2010).

9454

3500

0.00

, -91

.28

9459

0000

0.00

, -90

.13

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

9.25E+08 9.30E+08 9.35E+08 9.40E+08 9.45E+08 9.50E+08 9.55E+08 9.60E+08 9.65E+08 9.70E+08 9.75E+08

Frequency(Hz)

Po

wer

(dB

m)

GSM Transmission at 950 MHz GSM transmission at 950 MHz

Power Line InterferencePower Line Interference

11KV/415V AC 3 Phase Transformer : 11KV/415V AC 3 Phase Transformer : Power line interference measured using Power line interference measured using

Ultrasound detectorUltrasound detector

Transformer installationTransformer installation Ultrasound detectorUltrasound detector

Accurate and efficient in pin- pointing problems with disc, pin insulators, fuse links and cut joints at transformer sites.

W06 W05 W04 W03W02

W01

Survey of transformers along the Survey of transformers along the GMRT West armGMRT West arm

Survey of 3 Phase Transformer Survey of 3 Phase Transformer installation along GMRT antennas ( 16installation along GMRT antennas ( 16thth

March 2010March 2010 ) )SR. ANTENNAS TRANSFORMERS PROBLEMATIC AVERAGE GOOD

NO.   ATTENDED      

1 EAST ARM 5 E-02,E-05   E-03,E-04,E-06

2 WEST ARM 6 W-01,W-03   W-02,W-04,W-05,W-06

3 SOUTH ARM 5 S-01   S-02,S-03,S-04,S-06

  TOTAL 16 5   11

SR. NO. DETAILS OF RADIATION EAST WEST SOUTH

1BAD 11KV DISC INSULATOR

  W-01  

2 BAD DO E-02 W-01  

3 BAD TRANSFORMER E-02,E-05 W-01, W03 S-01

4 BAD H.T. BUSHING PIN INSULATOR   W-01  

5 BAD L.T. BUSHING PIN INSULATOR   W-01  

Uses measurements made with the GMRT for the localisation of RFI.

An RFI map with the GMRT Software backend at An RFI map with the GMRT Software backend at 150 MHz150 MHz

A Technique developed by Ue-Li Pen and collaborators forEpoch of Reionization work at the GMRT.

Uses measurement made with Interferometer for localizationof RFI

Antenna location are marked in red

Location of RFI sources are marked in blue

Hanging stray wire on Hanging stray wire on 440 KV AC EHT line440 KV AC EHT line

Hanging stray wire on 440 KV AC EHT line

Abandoned Telephone line near Abandoned Telephone line near HT lineHT line

SummarySummary The GMRT is located in a region of high population density, The GMRT is located in a region of high population density,

and must hence co-exist with multiple sources of RFI. and must hence co-exist with multiple sources of RFI.

The primary sources of RFI at GMRT are from cellular phone The primary sources of RFI at GMRT are from cellular phone transmissions, power line signals, and TV boosters. transmissions, power line signals, and TV boosters.

Regular field surveys have been carried out to locate sources Regular field surveys have been carried out to locate sources of strong RFI. Direct repairs of individual TVs were used to of strong RFI. Direct repairs of individual TVs were used to solve the problem of malfunctioning TV boosters.solve the problem of malfunctioning TV boosters.

Close interaction with the Cell phone operators have resulted Close interaction with the Cell phone operators have resulted in a significant fraction of these transmission being shifted to in a significant fraction of these transmission being shifted to 1800MHz, out side the GMRT bands. 1800MHz, out side the GMRT bands.

Similar interactions with electric companies have been used Similar interactions with electric companies have been used to repair malfunctioning to repair malfunctioning power line transformres. power line transformres.

SummarySummary cont…cont…

Close interaction with the Cell phone operators have Close interaction with the Cell phone operators have resulted in a significant fraction of these transmission resulted in a significant fraction of these transmission being shifted to 1800MHz, out side the GMRT bands. being shifted to 1800MHz, out side the GMRT bands.

Similar interactions with electric companies have been Similar interactions with electric companies have been used to repair malfunctioning power line transformersused to repair malfunctioning power line transformers

RFI environment at GMRT is still quite acceptable for RFI environment at GMRT is still quite acceptable for cutting-edge low frequency radio astronomy. The cutting-edge low frequency radio astronomy. The frequency range is now being extended to cover 250-frequency range is now being extended to cover 250-500 MHz and 550-900 MHz and there are no obvious 500 MHz and 550-900 MHz and there are no obvious show-stoppers from the RFI point of view that will limit show-stoppers from the RFI point of view that will limit system performance.system performance.