Broadcast relay station
A broadcast relay station, also known as a satellite station, relay transmitter, broadcast translator (U.S.), re-broadcaster (Canada), repeater (two-way radio) or complementary station (Mexico), is a broadcast transmitter which repeats (or transponds) the signal of a radio or television station to an area not covered by the originating station.
"Relay transmitter" redirects here. For other uses, see Relay (disambiguation) and Repeater (disambiguation).
These expand the broadcast range of a television or radio station beyond the primary signal's original coverage or improves service in the original coverage area. The stations may be (but are not usually) used to create a single-frequency network. They may also be used by an AM or FM radio station to establish a presence on the other band.
Relay stations are most commonly established and operated by the same organisations responsible for the originating stations they repeat. Depending on technical and regulatory restrictions, relays may also be set up by unrelated organisations.
Types[edit]
Translators[edit]
In its simplest form, a broadcast translator is a facility created to receive a terrestrial broadcast over the air on one frequency and rebroadcast the same (or substantially identical) signal on another frequency. These stations are used in television and radio to cover areas (such as valleys or rural villages) which are not adequately covered by a station's main signal. They can also be used to expand market coverage by duplicating programming on another band.
Boosters and distributed transmitters[edit]
Relays which broadcast within (or near) the parent station's coverage area on the same channel (or frequency) are known in the U.S. as booster stations. Signals from the stations may interfere with each other without careful antenna design. Radio interference can be avoided by using atomic time, obtained from GPS satellites, to synchronize co-channel stations in a single-frequency network.
Analog television stations cannot have same-channel boosters unless opposite (perpendicular) polarization is used, due to video synchronization issues such as ghosting. In the U.S., no new on-channel UHF signal boosters have been authorized since July 11, 1975.[1]
A distributed transmission system (DTS or DTx) uses several medium-power stations (usually digital) on the same frequency to cover a broadcast area, rather than one high-power station with repeaters on a different frequency. Although digital television stations are technically capable of sharing a channel, this is more difficult with the 8VSB modulation and unvariable guard interval used in ATSC standards than with the orthogonal frequency-division multiplexing (OFDM) used in the European and Australian DVB-T standard. A distributed transmission system would have stringent synchronization requirements, requiring each transmitter to receive its signal from a central source for broadcast at a GPS-synchronized time. A DTS does not use broadcast repeaters in the conventional sense, since they cannot receive a signal from a main terrestrial broadcast transmitter for rebroadcast; to do so would introduce a re-transmission delay destroying the required synchronization, causing interference between transmitters.
The use of virtual channels is another alternative, although this may cause the same channel to appear several times in a receiver – once for each relay station – and require the user to tune to the best one (which may change due to propagation issues such as weather). Although boosters or DTS cause all relay stations to appear as one signal, they require careful engineering to avoid interference.
Satellite stations[edit]
Some licensed stations simulcast another station. Relay stations in name only, they are generally licensed like any other station. Although this is unregulated in the U.S. and widely permitted in Canada, the U.S. Federal Communications Commission (FCC) regulates radio formats to ensure diversity in programming.
U.S. satellite stations may request an FCC exemption from requirements for a properly staffed broadcast studio in the city of license. The stations often cover large, sparsely populated regions or operate as statewide non-commercial educational radio and television systems.
Semi-satellites[edit]
A television re-broadcaster often sells local (or regional) advertising for broadcast only on the local transmitter, and may air a limited amount of programming distinct from its parent station. Some "semi-satellites" broadcast local news or separate news segments during part of the newscast. CHEX-TV-2 in Oshawa, Ontario, aired daily late-afternoon and early-evening news and community programs separate from its parent station, CHEX-TV in Peterborough, Ontario.[2] The FCC prohibits this on U.S. FM translator stations, only permitting it on fully licensed stations.
In some cases, a semi-satellite is a formerly autonomous full-service station which is programmed remotely through centralcasting or broadcast automation to avoid the cost of a local staff. CBLFT, an owned-and-operated station of the French-language network Ici Radio-Canada Télé in Toronto, is a de facto semi-satellite of its stronger Ottawa sibling CBOFT; its programming has long been identical or differed only in local news and advertising. A financially weak privately owned broadcaster in a small market can become a de facto semi-satellite by gradually curtailing local production and relying on a commonly owned station in a larger city for programming; WWTI in Watertown, New York, relies on WSYR-TV in this manner. Broadcast automation allows the substitution of syndicated programming or digital subchannel content which the broadcaster was unable to obtain for both cities.
Some defunct full-service stations (such as CJSS-TV in Cornwall, Ontario, now CJOH-TV-8) have become full satellite stations and originate nothing. If programming from the parent station must be removed or substituted due to local sports blackouts, the modified signal is that of a semi-satellite station.
National networks[edit]
Most broadcasters outside North America, portions of South America, and Japan maintain a national network, and use relay transmitters to provide service to a region (or nation). Compared with other types of relays, the transmitter network is often created and maintained by an independent authority (funded with television license fees); several major broadcasters use the same transmitters.
In North America, a similar pattern of regional network broadcasting is sometimes used by state- or province-wide educational television networks. A state or province establishes an educational station and extends it with several full-power transmitters to cover the entire jurisdiction, with no capability for local-programming origination. In the U.S., such regional networks are member stations of the national Public Broadcasting Service.
By country[edit]
Canada[edit]
In Canada, "re-broadcaster" or "re-broadcasting transmitter" are the terms most commonly used by the Canadian Radio-television and Telecommunications Commission (CRTC).