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There are two types ofradio network currently in use around the world: the one-to-many (simplex communication)broadcast network commonly used for public information andmass-media entertainment, and thetwo-way radio (duplex communication) type used more commonly for public safety and public services such aspolice, fire,taxicabs, and delivery services. Cell phones are able to send and receive simultaneously by using two different frequencies at the same time. Many of the same components and much of the same basic technology applies to all three.
The two-way type of radio network shares many of the same technologies and components as the broadcast-type radio network but is generally set up with fixed broadcast points (transmitters) with co-located receivers and mobile receivers/transmitters ortransceivers.[citation needed] In this way both the fixed and mobile radio units can communicate with each other over broad geographic regions ranging in size from small single cities to entire states/provinces or countries. There are many ways in which multiple fixed transmit/receive sites can be interconnected to achieve the range of coverage required by the jurisdiction or authority implementing the system: conventional wireless links in numerous frequency bands,fibre-optic links, or microwave links. In all of these cases the signals are typically backhauled to a central switch of some type where the radio message is processed and resent (repeated) to all transmitter sites where it is required to be heard.
In contemporary two-way radio systems, a concept calledtrunking is commonly used to achieve better efficiency of radio spectrum use. It provides a very wide range of coverage, with no switching of channels required by the mobile radio user as it roams throughout the system coverage. Trunking of two-way radio is identical to the concept used forcellular phone systems where each fixed and mobile radio is specifically identified to the system controller and its operation is switched by the controller.
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The broadcast type of radio network is a network system which distributesradio programming to multiplestations simultaneously, or slightly delayed, for the purpose of extending total coverage beyond the limits of a single broadcast signal. The resulting expanded audience for radio programming or information essentially applies the benefits ofmass-production to thebroadcasting enterprise. A radio network has two sales departments, one to package and sell programs to radio stations, and one to sell the audience of those programs to advertisers.
Most radio networks also produce much of their programming. Originally, radio networks owned some or all of the stations that broadcast the network'sradio format programming. Presently however, there are many networks that do not own any stations and only produce and/or distribute programming. Similarly station ownership does not always indicate network affiliation. A company might own stations in several different markets and purchase programming from a variety of networks.
Radio networks rose rapidly with the growth of regular broadcasting of radio to home listeners in the 1920s. This growth took various paths in different places. InBritain theBBC was developed withpublic funding, in the form of abroadcast receiver license, and a broadcastingmonopoly in its early decades. In contrast, in theUnited States various competingcommercial broadcasting networks arose funded byadvertising revenue. In that instance, the same corporation that owned or operated the network often manufactured and marketed the listener's radio.
Major technical challenges to be overcome when distributing programs over long distances are maintaining signal quality and managing the number of switching/relay points in thesignal chain. Early on, programs were sent to remote stations (either owned or affiliated) by various methods, including leasedtelephone lines, pre-recordedgramophone records and audio tape. The world's first all-radio, non-wireline network was claimed to be theRural Radio Network, a group of sixupstate New YorkFM stations that began operation in June 1948. Terrestrialmicrowave relay, a technology later introduced to link stations, has been largely supplanted bycoaxial cable,fiber, andsatellite, which usually offer superior cost-benefit ratios. Many early radio networks evolved intotelevision networks.
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