Editing Base station (section)

==== Professional ====

In professional two-way radio systems, a base station is used to maintain contact with a [[Dispatch (logistics)|dispatch]] fleet of [[Walkie talkie|hand-held]] or [[Mobile radio|mobile]] radios, and/or to activate one-way paging receivers. The base station is one end of a communications link. The other end is a movable vehicle-mounted radio or walkie-talkie.<ref>"Evaluating Regional Alternatives: Systems Design Considerations," ''Planning Emergency Medical Communications: Volume 2, Local/Regional Level Planning Guide'', (Washington, D.C.: National Highway Traffic Safety Administration, US Department of Transportation, 1995) pp. 39–43.</ref> Examples of base station uses in two-way radio include the dispatch of [[tow truck]]s and [[taxicab]]s.

[[File:Base station 2 channel block diagram.svg|left|thumb|500px|Basic base station elements used in a remote-controlled installation. [[Selective calling]] options such as CTCSS are optional.]]Professional base station radios are often one channel. In lightly used base stations, a multi-channel unit may be employed.<ref>Block diagram is from: "Figure 2: Two Channel VHF Base Station," ''Planning Emergency Medical Communications: Volume 2, Local/Regional Level Planning Guide'', (Washington, D.C.: National Highway Traffic Safety Administration, US Department of Transportation, 1995) pp. 42.</ref> In heavily used systems, the capability for additional channels, where needed, is accomplished by installing an additional base station for each channel. Each base station appears as a single channel on the dispatch center control console. In a properly designed dispatch center with several staff members, this allows each dispatcher to communicate simultaneously, independently of one another, on a different channel as necessary. For example, a taxi company dispatch center may have one base station on a high-rise building in [[Boston, Massachusetts|Boston]] and another on a different channel in [[Providence, Rhode Island|Providence]]. Each taxi dispatcher could communicate with taxis in either Boston or Providence by selecting the respective base station on his or her console.<ref>Base stations in land mobile systems are often located at remote sites such as hilltops or water towers. Some are controlled from two or more locations. For example, a base station used to communicate with taxis may be connected to remote control consoles at both a taxi company office and an answering service for after-hours calls. The taxi company and answering service may be miles apart. Single channel base stations reduce confusion by eliminating the possibility that the wrong channel may be selected.</ref>

In dispatching centers it is common for eight or more radio base stations to be connected to a single dispatching console. Dispatching personnel can tell which channel a message is being received on by a combination of local protocol, unit identifiers, volume settings, and busy indicator lights. A typical console has two speakers identified as ''select'' and ''unselect''. Audio from a primary selected channel is routed to the select speaker and to a headset. Each channel has a busy light which flashes when someone talks on the associated channel.<ref>To read more about multi-channel consoles, look at the service manual for a relatively simple console: ''8-Channel Remote Console, 120, 220, 240 V AC or 12 V DC T16167 AM or BM'', 68-81021E80, (Schaumburg, Illinois: Motorola, Inc. 1980.) This is a relatively simple analog console compared to large, enterprise-level Centracom-series units.</ref>

Base stations can be local controlled or remote controlled. Local controlled base stations are operated by front panel controls on the base station cabinet. Remote control base stations can be operated over tone- or [[4-20 mA#Two-way radio use|DC-remote]] circuits. The dispatch point console and remote base station are connected by leased private line telephone circuits, (sometimes called ''RTO circuit''s), a [[Digital Signal 1|DS-1]], or radio links.<ref>The term ''RTO circuit'' is legacy jargon and comes from Bell System billing terminology. RTO circuits refer to analog radio remote control and radio broadcast leased telephone circuits.</ref> The consoles multiplex transmit commands onto remote control circuits. Some system configurations require duplex, or four wire, audio paths from the base station to the console. Others require only a two-wire or half duplex link.<ref>For a brief discussion of remote controlled base stations, see: "Evaluating Regional Alternatives: Systems Design Considerations," ''Planning Emergency Medical Communications: Volume 2, Local/Regional Level Planning Guide'', (Washington, D.C.: National Highway Traffic Safety Administration, US Department of Transportation, 1995) pp. 39–41. Tone remote controls are described in this section.</ref>

[[File:Base station antenna network.svg|right|thumb|230px|The diagram shows a [[band-pass filter]] used to reduce the base station [[Receiver (radio)|receiver's]] exposure to unwanted signals. It also reduces the transmission of undesired signals. The [[Circulator|isolator]] is a one-way device which reduces the ease of signals from nearby transmitters going up the antenna line and into the base station [[transmitter]]. This prevents the unwanted mixing of signals inside the base station transmitter which can generate interference.]] Interference could be defined as receiving any signal other than from a radio in your own system. To avoid interference from users on the same channel, or interference from nearby strong signals on another channel, professional base stations use a combination of:<ref>Block diagram is from: "Figure 8: Bandpass Cavity/Isolator Location," ''Planning Emergency Medical Communications: Volume 2, Local/Regional Level Planning Guide'', (Washington, D.C.: National Highway Traffic Safety Administration, US Department of Transportation, 1995) pp. 57.</ref><ref>Bulleted items condensed from, "EMS Communications," "System Coordination," and "Site Engineering," in ''Planning Emergency Medical Communications: Volume 2, Local/Regional Level Planning Guide'', (Washington, D.C.: National Highway Traffic Safety Administration, US Department of Transportation, 1995) pp. 10–19, 55–58.</ref>
* minimum receiver specifications and filtering.<ref>For an example of receiver specifications, see, "Table 9-3," ''800 MHz Trunked Radio Request for Proposals: Public Safety Projects Office,'' (Oklahoma City, Oklahoma: Oklahoma City Municipal Facilities Authority, 2000, pp. 181.</ref><ref>A list of types of filtering used to prevent interference between equipment at the same site is included in "6.2.4 Electromagnetic Compatibility Studies," ''800 MHz Trunked Radio Request for Proposals: Public Safety Projects Office,'' (Oklahoma City, Oklahoma: Oklahoma City Municipal Facilities Authority, 2000, pp. 119.</ref><ref>More detail of interference reduction equipment is provided in, "9.1.2 Base Station/Mobile Relay, 800 MHz," ''800 MHz Trunked Radio Request for Proposals: Public Safety Projects Office,'' (Oklahoma City, Oklahoma: Oklahoma City Municipal Facilities Authority, 2000, pp. 165–168.</ref>
* analysis of other frequencies in use nearby.
* in the US, coordination of shared frequencies by coordinating agencies.<ref>For example, US federal government systems are coordinated and licensed by the [[National Telecommunications and Information Administration]]. [[Business band|Business/Industrial Pool]] licenses are coordinated by the Personal Communications Industry Association (PCIA) and licensed by the Federal Communications Commission.</ref>
* locating equipment so that terrain blocks interfering signals.
* use of directional antennas to reduce unwanted signals.

Base stations are sometimes called ''control'' or ''fixed'' stations in US [[Federal Communications Commission]] licensing. These terms are defined in regulations inside Part 90 of the commissions regulations. In US licensing jargon, types of base stations include:
* A '''fixed''' station is a base station used in a system intended only to communicate with other base stations. A ''fixed'' station can also be radio link used to operate a distant base station by remote control. (No mobile or hand-held radios are involved in the system.)
* A '''control''' station is a base station used in a system with a repeater where the base station is used to communicate through the repeater.
* A '''temporary base''' is a base station used in one location for less than a year.
* A '''[[Radio repeater|repeater]]''' is a type of base station that extends the range of hand-held and mobile radios.