Invasion of Radio Frequency Interference

© Dr. Steve Rapp 2009


TopicsTopics•Electromagnetic SpectrumElectromagnetic Spectrum•Gathering Signals; Radio SourcesGathering Signals; Radio Sources•How a Radio Telescope WorksHow a Radio Telescope Works•What is RFI; RFI LinksWhat is RFI; RFI Links•Monitoring RFIMonitoring RFI•Quiet Skies Goals Quiet Skies Goals •How to Measure RFI; RFI DetectorsHow to Measure RFI; RFI Detectors•DemonstrationsDemonstrations•Spectrum Allocation LinksSpectrum Allocation Links•On-line ForumOn-line Forum


The Electromagnetic Spectrum Covers a Broad Range of Wavelengths

Hertz


Gathering In The Signals

• First cosmic radio waves: Karl Jansky, 1932• First dish-shaped radio telescope: Grote Reber, 1937• Radio Sources: certain regions of the sky seem to

emit more radio energy than their surroundings

A replica of the Jansky Telescope sits outside the dormitory at NRAO.


Radio Sources Include:• Stars, nebulae, galaxies, quasars, pulsars,

the sun and its planets, as well as clouds of molecules between the stars.

Grote Reber built the first dish type antenna in 1937 to detect radio sources in the Milky Way Galaxy. This is a picture of the original telescope that Reber built for about $4000. It is located at the NRAO in Green Bank, WV.


How a Radio Telescope Works• Radio waves are reflected from a parabolic shaped metal surface.

Optical telescopes (reflectors) use a glass mirror to reflect light waves. (Demo)


Radio Waves Are Reflected To A Focal Point

Radio Waves Radio Waves

Parabolic Shaped Dish


How a Radio Telescope Works

• The larger the reflecting surface, the greater The larger the reflecting surface, the greater the amount of energy gathered.the amount of energy gathered.

• Radio waves are focused on a feed horn.Radio waves are focused on a feed horn.

• Radio signals converted to electrical current Radio signals converted to electrical current in amplifiers (front ends).in amplifiers (front ends).

• Currents sent to control room and amplified Currents sent to control room and amplified by backends.by backends.

• Computer processing.Computer processing.



•RFI is any electromagnetic signal not of RFI is any electromagnetic signal not of cosmic origin.cosmic origin.•Any thing that produces an electric arc Any thing that produces an electric arc produces broadband radio frequencies.produces broadband radio frequencies.•Radio astronomy is very susceptible to RFI Radio astronomy is very susceptible to RFI from active services (i.e. satellites, cell from active services (i.e. satellites, cell phone towers, etc.) especially since radio phone towers, etc.) especially since radio telescopes receive signals on the order of telescopes receive signals on the order of 101099 times weaker than signals from active times weaker than signals from active services.services.

What is Radio Frequency Interference (RFI)?


Learning About RFILearning About RFI

• Local Interference Studies: Local Interference Studies: The Quiet Skies Project

• Green Bank Interference Group: Green Bank Interference Group: http://www.cv.nrao.edu/~rfisher/ipg.html

• Radio Astronomy and Interference: Radio Astronomy and Interference: http://www.nrao.edu/index.php/learn/radioastronomy/interference

• Radio Frequency Interference and Telescopes:Radio Frequency Interference and Telescopes:

http://www.nrao.edu/index.php/learn/radioastronomy/radiotelescopes

http://steverapp.pageout.net/page.dyn/student/course/course_home?course_id=118047

http://www.cv.nrao.edu/~rfisher/ipg.html

http://www.nrao.edu/index.php/learn/radioastronomy/interference

http://www.nrao.edu/index.php/learn/radioastronomy/interference




Corrosion within the Cable TV Line Connector can allow RFI problems.

Monitoring Local RFI


Chasing Down Power Line RFIChasing Down Power Line RFI


Any Electrical Arc Can Cause RFIAny Electrical Arc Can Cause RFI

Arcing may occur in the wire wrap.

Faulty insulators may leak RFI


Faulty Lightning Arrestors And Power Transformers Can Produce RFI


Major Frequencies Invaded: 800, 900, 1420, 1665 MHz


Monitoring RFI at the GBT


Cell Tower Inspections

• Harman, WV

Checking out the antenna direction. We checked GPS coordinates, power levels, and cell tower estimated heights.



The Quiet Skies Project GoalsThe Quiet Skies Project Goals• Students will measure interference levels at their Students will measure interference levels at their

schools and in their communities; schools and in their communities; • Reduce and transmit their data to an NRAO or a Reduce and transmit their data to an NRAO or a

Linwood Holton Governor’s School data base; Linwood Holton Governor’s School data base; http://www.gb.nrao.edu/php/quietskies/ http://www.gb.nrao.edu/php/quietskies/

• Use online spectrum allocation data, and local Use online spectrum allocation data, and local information to determine possible causes of information to determine possible causes of interference in their area; interference in their area;

• Analyze the complex trade-offs between radio Analyze the complex trade-offs between radio astronomy's need for quiet skies, and other astronomy's need for quiet skies, and other commercial, and non-commercial uses of the commercial, and non-commercial uses of the spectrum and share their insights with others. spectrum and share their insights with others.

Anatomy of a Quiet Skies DetectorAnatomy of a Quiet Skies Detector


How Do You Measure RFIHow Do You Measure RFI• RFI is measured in dBm.RFI is measured in dBm.• dBm is an abbreviation for the power ratio in dBm is an abbreviation for the power ratio in

decibel (dB) of the measured power decibel (dB) of the measured power referenced to one milliwatt (mW). referenced to one milliwatt (mW).

• One dBm is equal to 1 mW while -10 dBm is One dBm is equal to 1 mW while -10 dBm is equal to 100 equal to 100 µW.µW.

• The Quiet Skies Project Article, published in The Quiet Skies Project Article, published in the October, 2008 issue of the October, 2008 issue of The Science The Science Teacher:Teacher: http://www.pageout.net/user/www/s/t/steverahttp://www.pageout.net/user/www/s/t/steverapp/p62-66rapp.pdf pp/p62-66rapp.pdf


Using the Quiet Skies DetectorUsing the Quiet Skies Detector

• Directions:

• Data Table:Data Table:

• Things to Accomplish:

• Assessment:

http://steverapp.pageout.net/user/www/s/t/steverapp/Quiet%20Skies%20Detector%20Directions.doc

http://steverapp.pageout.net/user/www/s/t/steverapp/Quiet%20Skies%20Project%20Directions.doc

http://steverapp.pageout.net/user/www/s/t/steverapp/QS%20Assessmentr.doc


NRAO Green Bank 800 42 2769/844 38.26.02N 79.49.05W

Radio Quiet Zone 900 43 2769/844 38.26.02N 79.49.05W

100 ft from 40 ft scope

1420 40 2769/84438.26.02N 79.49.05W

Lauren, Ben, Adam

1665 40 2769/84438.26.02N 79.49.05W

J.J. Kelly High 800 34 2454/748 36.98.01N 82.58.03W

Football field 900 35 2454/748 36.98.01N 82.58.03W

Mobeen 1420 31 2454/748 36.98.01N 82.58.03W

1665 342454/748

36.98.01N 82.58.03W

Location

Radio Frequency

(MHz)

Average Power (-dBm)

Elevation (feet/

meters)Latitude (d, m, s)

Longitude (d, m, s)

Date Sheet Available Online at: http://steverapp.pageout.net/page.dyn/student/course/web_links?course_id=118047


Quiet Skies RFI DemonstrationsQuiet Skies RFI Demonstrations

• PC and portable radio tuned to an AM channel- cover in foil- any difference?

• Battery connected to two wires, bring wires into contact next to tuned AM radio.

• Loosen coaxial cable from TV- bring portable radio close by and tune to FM station.

• Email your report about your experience with any of the above.


Spectrum Allocation LinksSpectrum Allocation Links

• Allocations in the U.S.: Allocations in the U.S.: http://www.jneuhaus.com/fccindex/spectrum.html

• U.S. Frequency Allocation Chart: U.S. Frequency Allocation Chart: http://www.ntia.doc.gov/osmhome/allochrt.html

• Radio Astronomy Frequencies:Radio Astronomy Frequencies: http://www.astron.nl/craf/threats.htm

http://www.jneuhaus.com/fccindex/spectrum.html

http://www.jneuhaus.com/fccindex/spectrum.html

http://www.ntia.doc.gov/osmhome/allochrt.html

http://www.ntia.doc.gov/osmhome/allochrt.html

http://www.astron.nl/craf/threats.htm


On-Line Forum for Anecdotal DataOn-Line Forum for Anecdotal Data

http://steverapp.pageout.net/page.dyn/discussion/view_forum?forum_id=15066&course_id=118047

© Dr. Steve Rapp 2009Thank you for your attention!

Documents

Invasion of Radio Frequency Interference