Microwave
General notes
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- Occupy frequencies between about 1GHz and 3000GHz.
- Short wavelengths microwaves behave like light. Naturally travel in straight lines and can easily be disturbed by solid objects in their path.
- Higher frequency waves (those closer to 30GHz)—suitable for point to point applications including, high capacity ground based microwave and satellite where the waves new aimed from a single transmitter to a single receive.
- Middle frequency waves (closer to 15GHz)—used for satellite to multiple ground applications such as Satellite TV. E.g. Foxtel transmits digital TV from the satellite at frequencies around 12.4GHz.
- Lower frequency waves (Radio Frequency waves) — suited for local broad coverage applications. Such as mobile phones and WLAN network. At lower frequencies the waves are better able to penetrate local structures such as buildings. For lower frequency applications the power level of the transmitters can be adjusted to alter the radius of the effective coverage area.
- To maximise coverage Global Positioning Satellites (GPS) transmit in the range 1GHz and 1.5GHz.
- To reduce interference, frequency ranges are legally specified for different applications. The Australian Communication Authority (ACA) specifies and enforces how different frequency ranges can be used in Australia. The International Telecommunications Union (ITU) allocates frequencies internationally.
Advantages and disadvantages of microwaves
Advantages
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Disadvantages
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Point to point terrestial microwave
Point to Point Terrestrial Microwave — used to relay wireless signals across large distances. NOTE: Optic fibre is replacing many voice and data terrestrial microwave systems with satellite replacing many broadcast radio and TV applications.
- The use of terrestrial microwave transmission commenced during the 1950s and was a commonplace during 1980s. It is used to relay radio and TV programs between different radio and TV stations and also relay telephone signals
- A direct and uninterrupted line of sight between the transmitter and the receiver is required.
- Transponders (sequences of transmitter/receivers) are arranged into chain, so that each transponder receives the signal, amplifies it and transmits it precisely to the next transponder.
- Transponders must be physically located high above the local ground level to avoid trees, buildings and other large obstacles. Microwave transponders are installed on purpose built communication towers—usually on the same tower with mobile phone base station transmitters.