Unguided Media Flashcards
What are some Common uses of wireless
transmission/unguided media for
information communications
Broadcast: TV and radio
Telecommunications (Terrestrial
and Satellite)
Infrared e.g. TV remote
Private business networks
What are the types of unguided media for wireless transmission
Radio
Microwave
Infrared
Describe unguided media
Unguided media transport electromagnetic waves without using a
physical conductor. i.e. the signal is not confined to a physical
conduit or channel
What are the different forms of electromagnetic waves that are used to transmit data
radio, satellite microwave, Bluetooth and infrared light.
How is Transmission and reception are achieved using an antenna
Transmitter sends out the electromagnetic signal into the
medium (atmosphere, water, space)
Receiver picks up the signal from the surrounding medium
What is an antennae
An antenna can be defined as an electrical conductor or system of
conductors used to radiate or collect electromagnetic energy.
How does an antennae transmit and receive a signal
- To transmit a signal –radio frequency energy from the transmitter is
converted to electromagnetic energy by the transmission antenna
and radiated into the surrounding environment. - To receive a signal - electromagnetic energy impinging on the
reception antenna is converted to radio frequency electrical energy
and fed to the receiver. - The same antenna is often used for both purposes
Describe directional transmission
- Transmitter sends out a focused electromagnetic beam
- Transmitter and receiver antennae must be carefully aligned
- More suitable for higher frequency signals
Describe omnidirectional transmission
- Transmitted signal spreads out in all directions
- May be received by many antennae
Describe the Wireless Transmission Frequencies
Microwave (300Mhz to 3 GHz )
* Has extremely short wavelength
* Uses highly directional beams
* Suitable for point to point transmission
* Used for satellite communications
Radio (3kHz to 300GHz)
* Suitable for omnidirectional applications
* Broadcast radio ranges e.g. AM and FM radio bands
Infrared (3 x 10^11 to 2 x 10^14Hz)
* Invisible light waves whose frequencies is bellow that of red light
* Requires line of sight
* Is affected by heavy rain
* Useful for local point-to-point and multipoint applications within confined
areas
Describe the terrestrial microwave
- The most common type of microwave antenna is the parabolic
“dish.” A typical size is about 3 m in diameter - The antennas are usually located at substantial heights above
ground level to extend the range between antennas and to be
able to transmit over intervening obstacles. - Focuses a narrow beam: to achieve line-of-sight transmission to
the receiving antenna
What are the applications of the terrestrial microwave
- The primary use for terrestrial microwave systems is in long-haul
telecommunications service, as an alternative to coaxial cable or
optical fiber. Higher frequencies give higher data rates. - Requires far fewer amplifiers or repeaters than coaxial cable over
the same distance, but requires line-of-sight transmission. - short point-to-point links between buildings, for closed-circuit TV
or as a data link between local area networks.
Describe the satellite microwave
- A communication satellite is a microwave relay station between
two or more ground stations (also called earth stations). - Receives on one frequency, amplifies or repeats signal and
transmits on another frequency e.g. uplink 5.925-6.425 GHz &
downlink 3.7-4.2 GHz - Typically requires geo-stationary orbit about a height of 35,784km:
A single orbiting satellite can operate on a number of frequency
bands, known as transponder channels or transponders
*See page 5 for illustration
What are some applications of the satellite microwave
- Television distribution
- Long distance telephone transmission
- Private business networks
- Global positioning systems (GPS)
Describe broadcast radio
- Radio Frequencies range from 3KHz to 300GHz
- Broadcast radio frequencies - 30MHz to 1GHz
(covers VHF and UHF television and FM radio) - Unlike microwave;
broadcast radio is omnidirectional
broadcast radio does not require dish-shaped antennas
the antennas need not be rigidly mounted to a precise alignment - Transmission is limited to the line of sight
- Suffers from multipath interference
