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Radio Frequencies

Radio Frequencies. Oscillator. Feedback loop. Oscillator. As the output of the amplifier is fed to the input, feedback or oscillation occurs. Tuned Oscillator. Oscillator. When properly tuned to a high enough frequency, the oscillator will produced radio frequencies

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Radio Frequencies

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  1. Radio Frequencies

  2. Oscillator Feedback loop

  3. Oscillator • As the output of the amplifier is fed to the input, feedback or oscillation occurs

  4. Tuned Oscillator

  5. Oscillator • When properly tuned to a high enough frequency, the oscillator will produced radio frequencies • Frequencies begin to take on the characteristics of radio frequencies (RF) at about 30,000 KHz • RF can travel great distances, and can be modulated to carry information (audio & video)

  6. RF • Antennae are conductive rods that will easily radiate RF • When the output of the oscillator is connected to an antenna, the electrons in the antenna begin to vibrate or oscillate at RF frequencies • Waves of electromagnetic radiation will emanate from the antenna at those RF frequencies (+30KHz)

  7. RF spectrum • Very Low Frequencies – 3 – 30 KHz • Low Frequencies 30 – 300 KHz • Medium frequencies 300 KHz – 3 MHz • High frequencies 3 – 30 MHz • Very High frequencies 30 MHz – 300 MHz • Ultra High frequencies 300 MHz – 3 GHz • Super High frequencies 3 – 30 GHz • Extremely High frequencies 30 – 300 GHz

  8. RF and beyond • As particles continue to accelerate, creating waves of decreasing wavelengths, energy takes on other characteristics • Infrared • Visible light – red, orange, yellow, green, blue, indigo, and violet • Ultraviolet • X-rays • Gamma rays • Cosmic rays

  9. Spectrum management • AM radio (MF) – 535 – 1705 KHz • Channels are 10 KHz • Radio receivers tune to the center frequency in the channel or carrier 540 560 550 565 535 545 555

  10. Spectrum management • FM radio (VHF) – 88 – 108 MHz • Channels are 200 KHz • Radio receivers tune to the center frequency in the channel or carrier 88.1 88.2 88.0 +/- 75 KHz deviation

  11. Spectrum management • TV (VHF and UHF) • Channels are 6 MHz • TV receivers tune to the center frequency in the channel or videocarrier • In this example: Channel 6 83.25 MHz video carrier (1.25 MHz above lower edge of channel) 88.0 82.0 (Audio 4.5 MHz +/- 25 KHz) (30 KHz above lower edge of channel)

  12. Spectrum management • http://frrl.files.wordpress.com/2010/11/frequency-allo-chart.jpg

  13. Calculating wavelength Velocity WL = Frequency Velocity = speed of light = 300,000,000 meters per second

  14. Calculating wavelength 300,000,000 WL = Frequency

  15. Calculating wavelength 300,000,000 WL = 102,500,000 WHIZ-FM – 102.5 MHz

  16. Calculating wavelength 300,000,000 2.93 = 102,500,000 Radio wave is 2.93 meters from crest to crest

  17. Calculating wavelength 300,000,000 2.93 = 102,500,000

  18. Calculating wavelength 300,000,000 WL = 1,240,000 WHIZ-AM – 1240 KHz

  19. Calculating wavelength 300,000,000 241.93 = 1,240,000 Radio wave is 241.93 meters from crest to crest

  20. Calculating wavelength • Higher frequencies = shorter wavelengths • In the highest bands of the usable spectrum, wavelength are measured in nanometers or angstroms • Wavelengths in the “microwave” bands are so short that atmospheric moisture affects transmission

  21. Calculating wavelength • These calculations are used to determine ideal antenna length • In FM and TV, antennae use half-wave dipole construction • The antenna is one-half the length of the wave, and the pole is cut in half

  22. Half wave dipole “Stacking” the elements forces waves toward horizon. This adds gain to the antenna.

  23. Quarter-wave vertical • In AM, the longer wavelengths dictate the use of quarter-wave vertical antennae • The tower itself becomes the antenna • AM also uses a ground array to propagate the ground waves

  24. How waves behave • HF and above (FM, TV, satellite, etc.) travel in direct waves, or line-of-sight • Direct waves will not “bend” or pass through solid objects • LF and MF frequencies travel in sky waves, which bounce off the ionosphere • LF and MF frequencies travel in ground waves, which follow the curvature of the earth

  25. Antenna location • Best location for an FM or TV antenna is on the highest unobstructed hill, building, tower, peak • Best location for an AM antenna is low marshy location

  26. Antenna schematics AM antenna FM antenna

  27. Ionosphere • A layer of the atmosphere where hydrogen atoms become “ionized” • Ionization occurs when the hydrogen atoms become “charged” because they give up electrons • Heating of the ionosphere by the sun causes the ionization • The will determine the behavior of sky waves

  28. Sky waves • May be absorbed during the daylight hours • May pass through during the daylight hours • May be reflected at night when the ionosphere cools

  29. Sunspots • Affect terrestrial communication, telecommunications, broadcasting, computers, other electronics • Occur in 11 year cycles • Activity builds and subsides slowly 1990 2000 2010

  30. Modulation

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