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Radio Transmission

Radio Transmission. Moving information from place to place using Electro Magnetic Radiation. Types of transmission. Amplitude Modulation Frequency Modulation Phase Modulation Pulse Code Modulation. AM Waveforms. FM Waveforms. The carrier.

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Radio Transmission

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Presentation Transcript

  1. Radio Transmission Moving information from place to place using Electro Magnetic Radiation

  2. Types of transmission.. • Amplitude Modulation • Frequency Modulation • Phase Modulation • Pulse Code Modulation

  3. AM Waveforms

  4. FM Waveforms

  5. The carrier.... • A high frequency ‘carrier’ takes information from one place to another. • The ‘carrier’ is considered to be a ‘radio frequency’ or RF. • The ‘information’ is attached to the carrier using AM, FM, or PCM or another method.

  6. The carrier is a Sine Wave

  7. Carrier velocity = v • The carrier travels at the speed of light • 186,000 miles/second • 300,000,000 meters/second

  8. Wavelength = v/f F = 1290 KHz ( WNBF Radio ) Λ = v/f = 300,000,000/1,290,000 = 232.5 meters

  9. Amplitude Modulation • Includes Broadcast Radio 540 KHz to 1640KHz • Citizen Band • Amateur Radio • Television Video

  10. Frequency Modulation • Broadcast FM from 88 MHz to 108 MHz • Aircraft, Marine, Taxi • Some digital transmissions • Television Audio • All Satellite Television

  11. Electro Magnetic Radiation

  12. Powerful Transmitters.. • 50 Kilo Watts into a large tower antenna • Can travel around the globe under certain weather conditions. • The signal strength is affected by many conditions including humidity, cloud cover and content, time of day, and the terrain.

  13. The receiver.... • Always has some type of antenna to catch the signal transmitted. • A radio direction finder has a ‘directional’ antenna. • The weak signal from the antenna is amplified. • The information is removed from the carrier.

  14. Noise is undesirable.. • Noise comes from many sources • It can interfere with the signal • AM is especially vulnerable • FM is preferred due to its immunity • TV Sound is FM, and generally quiet • AM Radio is often noisy- especially long distance reception.

  15. Parts of an AM Radio • Power Supply • Tuner - Selects a desired frequency • RF Amplifier • Frequency Converter • Intermediate Frequency Amplifier • Detector • Audio Amplifier

  16. Radio Waves - Wave Length • The speed of light.... • The frequency of the signal • The length of a wave • V = Lambda X F

  17. The speed of light... • 186,000 Miles per Second • 300,000,000 Meters / Second • 1 Foot/Nano Second • 1 Nano Second is 1 billionth of a second.

  18. Antennas are related to wavelength. • A quarter Wavelength... • Or multiples of a quarter wavelength used for best reception. • See part 2

  19. Satellite Television It’s out of sight! 22,300 miles in fact!

  20. From How Stuff Works

  21. 20 + Commercial Satellites • In Geo-Stationary Orbit 22,300 miles away.... • All in a band over the Equator • They have a revolution of once per day. • Just like us!... That makes them geo-stationary. • They have a useful life of 10 years.

  22. Boeing 702the most widely used satellite

  23. Hughes HS601

  24. Forces at work • A satellite spins around the planet • What holds these satellites in place ? • Gravity will try to pull the mass back to earth • The force of a centrifuge pushes the satellite out into space ..

  25. Geo-stationary Orbits • The force of gravity, Fg, is equal to • The centripetal force, Fc • AT 22,300 miles, Fg = Fc if the velocity is one revolution per day ! • This was first proposed byArthur C. Clarke...

  26. The Clarke Belt • These satellites appear to be in the same position in the sky at all times. • They are directly over the equator but not directly over us. • They are in a line that starts 14 degrees above our Western Horizon. • And rises to 42 degrees elevation in the South

  27. Original figure from Clarke's article in the October 1945 edition of Wireless World

  28. Elevation and Azimuth • The Elevation is the number of degrees above the horizontal... • The Azimuth is a degree reading with North being 0 and 360 degrees, East being 90, South at 180, and West at 270. • Degree readings are allways ‘True’ and not ‘Magnetic’

  29. Uplink antenna Elevation and Azimuth are adjusted to point to the satellite

  30. 24 Channels on a Satellite • Numbered 1 to 24 • Odd Number Channels are often Vertically Polarized... • Even Number Channels are often Horizontally Polarized. • The antenna must line up with the polarization..

  31. C Band and Ku Band • The C Band uses 4 GHz for the down link and 6 GHz for the up link. • The Ku Band uses 12 GHz for the down link and 14 GHz for the up link. • A ground station monitors each satellite 24 hours a day. • Friction tends to move them from their orbit ! (Magnetic friction..)

  32. A ‘downlink’ Much less expensive than the uplink ..

  33. Analog vs Digital • The largest commercial system is an Analog system, subject to noise and signal strength. • The newer Digital dishes can easily remove the nose and can produce crystal clear pictures with weak signals. • The Digital dishes are smaller..

  34. A digital dish .. MPEG2 is used as a format for the data stream ..

  35. A satellite uses 300 Watts • Which must come from solar power • This power is distributed over 24 small transmitters... • The surface area of the US is 3,000,000 Square Miles. • That’s 100 Micro Watts per square mile • But only 5 Micro Watts per channel...

  36. The signals are very very weak. • A large ‘dish’ is used to focus the power received onto a small 1.5 CM antenna.. • A 12 Foot dish, has an area of Pi X R2 or 108 Sq Feet. • Calculate the power the dish receives from a 300 Watt Satellite....

  37. An 18” Digital Dish... • Has a much smaller surface area • Receives a much smaller amount of power... • But delivers a better signal due to the cleanliness of ‘bits’ !

  38. Satellite ‘Sighting’ • We point the dish at specific azimuths and elevations to find a satellite. • From 14 Degrees Elevation and 270 Degrees Azimuth (W) • To 42 Degrees Elevation and 180 Degrees Azimuth (S) • A set of tables lets us find the data for a particular satellite.

  39. Latitude and Longitude • Binghamton... • Is at 70 Degrees E Longitude and 42 Degrees N Latitude • East of Grenich, and North of the Equator • The calculations for finding a satellite 22,300 miles over the equator are complex

  40. Longitudes for US View

  41. A recent copy of ORBIT • Shows us the longitude of the various satellites. • They are spaced 3 to 6 degrees apart • Their longitude, entered into an equation gives us Elevation and Azimuth.

  42. The Satellite RECEIVER • The signal is collected by the ‘dish’ • Focused on the ‘Feed Horn’ Assembly • Amplified by a Low Noise Amplifier • Converted to a much lower frequency • Carried by shielded cable to the receiver • And delivered to your TV set..

  43. Satellite Feed Horn Assembly

  44. The ‘Polarotor’ • A small motor turns the antenna to accomodate the ‘polarization’ of the signal. • The ‘plane’ of the signal ‘skews’ as we point the dish to the west • The ‘polarotor’ must compensate for this skew

  45. Satellites • Are also used for ‘Pager Service’ • Cellular Telephone • Other types of communication including the monitoring of vehicles like Federal Express • Global Positioning ( GPS)

  46. Satellite in low Earth Orbit

  47. For more .. Go to the web ..

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