Broadcast relay station
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.
Although boosters or DTS cause all relay stations to appear as one signal, they require careful engineering to avoid interference.
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.
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.
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.
The latter type officially includes the television station's -TV suffix between the call sign and the number, although it is often omitted from media directories.
The numbers are usually applied sequentially, beginning with "1", and denote the chronological order in which the station's rebroadcast transmitters began operation.
Translators which share a frequency (such as CBLT's former repeaters CBLET, CBLHT, CBLAT-2 and CH4113 on channel 12) are given distinct call signs.
Private commercial broadcasters operate full-power re-broadcasters to obtain "must carry" status on cable television systems.
Transmitters in small markets with one (or no) originating stations were, in most cases, not required to convert to digital even if operating at full power.
Transmitters broadcasting on UHF channels 52–69 were required to vacate the channels by August 31, 2011; some (such as a CKWS-TV re-transmitter in Brighton, Ontario, and three TVOntario sites) went digital as part of a move to a lower frequency but do not provide high-definition television, digital subchannels or any functions beyond that of the original analogue site.
Some stations licensed under the CRTC's experimental-broadcasting guidelines, a special class of short-term license (similar to special temporary authority) sometimes granted to newer campus and community radio operations, may have a call sign consisting of three letters from anywhere in Canada's ITU-prefix range followed by three digits (such as CFU758 or VEK565).
Former re-broadcasters have occasionally been converted to originating stations, retaining their former call sign; examples include CITE-FM-1 in Sherbrooke, CBF-FM-8 in Trois-Rivières and CBAF-FM-15 in Charlottetown.
The largest terrestrial radio-translator system in the U.S. in October 2008 belonged to KUER-FM, the non-commercial radio outlet of the University of Utah, with 33 translator stations ranging from Idaho to New Mexico and Arizona.
[9] Unlike FM radio, low-power television stations may operate as translators or originate their own programming.
The band was reallocated to cellular telephone services during the 1980s, with the handful of remaining transmitters moved to lower frequencies.
These exemptions are normally justified on the basis of economic hardship, where a rural location unable to support a full-service originating station may be able to sustain a full-power re-broadcaster.
Some stations (such as KVRR in Fargo, North Dakota) are chains of as many as four full-power transmitters, each with its own call sign and license, covering a large, sparsely-populated region.
Numbered broadcast translators which are moved to another frequency are normally issued new call signs to reflect the updated channel assignment.
By 2008, low- and full-power channel 55 licensees were encouraged to relocate early to free spectrum for Qualcomm's MediaFLO transmitters.
Any non-commercial station, even one with no local or educational content, can apply for an unlimited number of translators to be fed by any means (including satellite).
All other translators must be directly fed off the air, except for "fill-in" facilities in a primary station's service contour.
The ABC and SBS allow community-based relay transmitters to rebroadcast radio or television in areas which would otherwise have no service.
As a result, some areas have had trouble beginning digital or HD service due to problems with regional transmitters.
Terrestrially, the scenario is similar to Europe's; the systems are considered national networks, and are a collection of relay stations maintained by a government-funded authority.
