Communication Channels
- Information can be carried along different channels of communications such as:
- Wire pairs:
- Wire pairs are links between information transmitters and receivers
- They are used for low frequency, short distance communications
- They are subject to cross-talk
- Examples: doorbells, linking a telephone
- Coaxial cables:
- Coaxial cables are cables with two conducting wires in which a signal transmits through a central conductor that is surrounded by an insulator
- There is another outer conductor which is then surrounded by a plastic cover for insulation
- An earthed copper or aluminium braid (wire mesh) surrounds this, adding another layer of insulation to protect the signal from interference
- Example: connecting an aerial to a television
- Coaxial cables are much better for transmission of electrical signals than a wire pair, this is because they:
- Have a greater bandwidth
- Have less cross-talk
- Radiates less electromagnetic power
- Radio and microwave links:
- Line of sight transmission paths to receive and transmit information at microwave and radio frequencies
- Example: a microwave link can link a ground station to a satellite
- Optic fibres:
- A flexible, transparent fibre made by drawing glass or plastic
- A signal is transmitted through total internal reflection through the core (middle) of the fibre
- The fibre is surrounded by cladding to limit the risk of breakage
- Examples: high speed internet, medical devices eg. endoscope
Frequencies & Wavelengths in Communication Channels
- Wire pairs:
- Frequencies: 10 MHz
- Wavelengths: 30 m
- Coaxial cables:
- Frequencies: 2 MHz (phone), 1 GHz (TV)
- Wavelengths: 150 m – 0.3 m
- Radio and microwave links:
- Frequencies: 5 GHz
- Wavelengths: 6 cm
- Optic fibres:
- Frequencies: 104 GHz – 109 GHz
- Wavelengths: 0.03 m – 3.0 × 10-7 m
