3.3 Wireless (or, Unguided) Transmission Media

Transmissions and receptions are achieved by means of an antenna and can be

Directional Point-to-point focused beams employing high frequencies.

Omnidirectional Waves propagating in all directions using signals of lower frequencies.

Terrestrial Microwave

• Microwaves bend with the curvature of the earth

• Effective distance of microwave antenna

  

  3/4-adjustment factor for curvature of earth; h-hight of antenna;d measured in meters.

• Loss of energy due to attenuation (in deciBels) terrestrial microwave	-wavelength; d-length
  broadcast radio	-wavelength; d-length
  twisted pair	d
  coaxial cable	d

• Weather conditions and interference are a factor

• Used mainly for distance communication of voice and television transmission, and for short-point-to-point communications.

Satellite Microwave

A communication satellite:

• Is used for link ground stations

  point-to-point	broadcast

• Operates on a number of frequency bands, called transponder channels.
• Receives transmissions on one frequency band (uplink), and transmits on another frequency (downlink).
• Satellite period of rotation equals the earth's period of rotation At height of 34,784 km.
• Used for TV distribution, long-distance telephone, and business networks

Radio

Unlike microwave transmission that is directional, radio transmission is omnidirectional. The signals need simpler antennas.

Infrared

Transmitters and receivers (transceivers)

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