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personal radio service
A personal radio service is any system that allows individual to operate radio transmitters and receivers for personal purposes with minimal or no special license or individual authorization. Personal radio services exist around the world and typically use light-weight walkie talkie portable radios. The power output, antenna size, and technical characteristics of the equipment are set by regulations in each country.
Because radio spectrum allocation varies around the world, a personal radio service device may not be usable outside its original area of purchase. For example, US-specification Family Radio Service radios operate on frequencies that in Europe are allocated to fire and emergency services. Operation of a personal radio device that cause interference to other services may result in prosecution.
==Operating characteristics==
Specific details vary between the different national services, but many personal radio services operate in the UHF part of the radio spectrum, using frequency modulation and a maximum power of only a few watts. Operation is on predetermined channels. Unlike commercial business, marine, aviation, or emergency services radio, all users in an area share access to the available channels, requiring cooperation for effective communications. Unlike amateur radio, experimentation with different types of apparatus, and modes of modulation is not permitted, and equipment must be factory-built and approved.
These services are different from cellular mobile telephone systems in that no infrastructure (towers, base stations) is required; communications is point-to-point directly between users. However, this also means that communication range is usually limited to line-of-sight propagation, a few kilometres (miles) under the best of circumstances, and much less in heavily built up urban areas. Also unlike mobile telephones, operation is push-to-talk; a user must wait for the shared frequency to be clear before transmitting, and all stations on the frequency may hear the transmission. Since both stations are on the same frequency, the receiving station cannot interrupt the transmitter until it has finished. Generally only voice transmission is allowed under personal radio service regulations, although tone and digital selective calling features are allowed in some countries, and some services permit digital data transmission.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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