Invasion Of Radio Frequency Interference

© Dr. Steve Rapp 2009

Topics •Electromagnetic Spectrum •Gathering Signals; Radio Sources •How a Radio Telescope Works •What is RFI; RFI Links •Monitoring RFI •Quiet Skies Goals •How to Measure RFI; RFI Detectors •Demonstrations •Spectrum Allocation Links •On-line Forum © Dr. Steve Rapp 2009

The Electromagnetic Spectrum Covers a Broad Range of Wavelengths

Hertz

© Dr. Steve Rapp 2009

Gathering In The Signals A replica of the Jansky Telescope sits outside the dormitory at NRAO.

• 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 © Dr. Steve Rapp 2009

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. © Dr. Steve Rapp 2009

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)

© Dr. Steve Rapp 2009

Radio Waves Are Reflected To A Focal Point Radio Waves

Radio Waves

Parabolic Shaped Dish

© Dr. Steve Rapp 2009

How a Radio Telescope Works • The larger the reflecting surface, the greater the amount of energy gathered. • Radio waves are focused on a feed horn. • Radio signals converted to electrical current in amplifiers (front ends). • Currents sent to control room and amplified by backends. • Computer processing.

© Dr. Steve Rapp 2009

© Dr. Steve Rapp 2009

What is Radio Frequency Interference (RFI)? •RFI is any electromagnetic signal not of cosmic origin. •Any thing that produces an electric arc produces broadband radio frequencies. •Radio astronomy is very susceptible to RFI from active services (i.e. satellites, cell phone towers, etc.) especially since radio telescopes receive signals on the order of 109 times weaker than signals from active services. © Dr. Steve Rapp 2009

Learning About RFI

• Local Interference Studies: The Quiet Skies Project • Green Bank Interference Group: http://www.cv.nrao.edu/~rfisher/ipg.html • Radio Astronomy and Interference: http://www.nrao.edu/index.php/learn/radioastronomy/ http://www.nrao.edu/index.php/learn/radioastronomy • Radio Frequency Interference and Telescopes:

http://www.nrao.edu/index.php/learn/radioastronomy/ http://www.nrao.edu/index.php/learn/radioastronomy © Dr. Steve Rapp 2009

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

© Dr. Steve Rapp 2009

Chasing Down Power Line RFI

© Dr. Steve Rapp 2009

Any Electrical Arc Can Cause RFI Faulty insulators may leak RFI

Arcing may occur in the wire wrap. © Dr. Steve Rapp 2009

Faulty Lightning Arrestors And Power Transformers Can Produce RFI

© Dr. Steve Rapp 2009

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

© Dr. Steve Rapp 2009

Monitoring RFI at the GBT

© Dr. Steve Rapp 2009

Cell Tower Inspections • Harman, WV

Checking out the antenna direction.

We checked GPS coordinates, power levels, and cell tower estimated heights.

© Dr. Steve Rapp 2009

© Dr. Steve Rapp 2009

The Quiet Skies Project Goals • Students will measure interference levels at their schools and in their communities; • Reduce and transmit their data to an NRAO or a Linwood Holton Governor’s School data base; http://www.gb.nrao.edu/php/quietskies/ • Use online spectrum allocation data, and local information to determine possible causes of interference in their area; • Analyze the complex trade-offs between radio astronomy's need for quiet skies, and other commercial, and non-commercial uses of the spectrum and share their insights with others. © Dr. Steve Rapp 2009

Anatomy of a Quiet Skies Detector

How Do You Measure RFI • RFI is measured in dBm. • dBm is an abbreviation for the power ratio in decibel (dB) of the measured power referenced to one milliwatt (mW). • One dBm is equal to 1 mW while -10 dBm is equal to 100 µW.

• The Quiet Skies Project Article, published in the October, 2008 issue of The Science Teacher: http://www.pageout.net/user/www/s/t/steverapp/

© Dr. Steve Rapp 2009

Using the Quiet Skies Detector

• • • •

Directions: Data Table: Things to Accomplish: Assessment: © Dr. Steve Rapp 2009

Location

Radio Average Frequency Power (MHz) (-dBm)

Elevation (feet/ meters)

Latitude (d, m, s)

Longitude (d, m, s)

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

2769/844

38.26.02N

79.49.05W

Lauren, Ben, Adam

1665

40

2769/844

38.26.02N

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

1420

31

2454/748

1665

34

Mobeen

2454/748

36.98.01N

82.58.03W

36.98.01N

82.58.03W

Date Sheet Available Online at: http://steverapp.pageout.net/page.dyn/student/course/web_links?course_id=118047 © Dr. Steve Rapp 2009

Quiet 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. © Dr. Steve Rapp 2009

Spectrum Allocation Links

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

• U.S. Frequency Allocation Chart: http://www.ntia.doc.gov/osmhome/allochrt. • Radio Astronomy Frequencies: http://www.astron.nl/craf/threats.htm

© Dr. Steve Rapp 2009

On-Line Forum for Anecdotal Data

http://steverapp.pageout.net/page.dy

© Dr. Steve Rapp 2009

Thank you for your attention!

© Dr. Steve Rapp 2009