Broadcast translator
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In broadcasting, a translator is an FM radio station or a TV station which acts as a full-duplex repeater. Just as a verbal translator (person) listens in one language and speaks in another, a broadcast translator receives a signal from one channel and transmits it again, usually on another channel or other frequency assignment. This is common in the Americas, especially in the United States, and in the mountains.
For example KQED-FM in San Francisco transmits on 88.5 MHz with its large main transmitter. Smaller transmitters, known as FM translators repeat the signal on 88.1 MHz in Martinez and Benicia and on 88.3 MHz in Santa Rosa.
Translators operate with power up to 250 watts, compared with 6,000 to 50,000 watts for the main station. So they cover relatively small areas. Many translators operate by picking the signal of the main station off the air with a directional antenna and sensitve receiver and directly retransmitting the signal. Some are authorized to use microwave, internet or satellite methods to receive the signal from the main station.
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Rules
The basic FCC regulations on translators are:
- No station may be translated to another band (i.e. from AM to FM).
- No translator or booster may transmit anything other than the live simulcast of its licensed parent station, except for emergency warnings (such as EAS), and 30 seconds per hour for fundraising.
- The parent station must identify all of its translators and boosters at 7-9am, 1pm, and 4-6pm; or each must be equipped with its own automated hourly ID device (audio or FSK).
- Maximum power is 250 watts ERP for a translator, and 20% of the parent station's power for a booster.
- It must go off the air if the parent station's signal is lost, to prevent dead air.
Commercial stations may not own their translators (except for boosters), or be translated outside of the parent station's area (they can only fill in where terrain blocks the signal). They also may not transmit in the FM reserved band from 88 to 92 MHz, where only noncommercial stations are allowed. Noncommercial stations may broadcast in the commercial band, however. Unlike commercial stations, they can also relay programming to translators via satellite, so long as those translators are in the reserved band. All stations may use any means to feed boosters.
All U.S. translator and booster stations are low-power and have a class D license, making them secondary to other stations (including the parent). They must accept any interference from full-power (100-watt or more on FM) stations, while not causing any of their own. Boosters must not interfere with the parent station within the community of license. Licenses are automatically renewed with that of the parent station and do not require separate applications, though each may still be challenged with a petition to deny.
Unlike FM, LPTV stations may operate as either translators or originate their own programming.
Boosters
Translators which broadcast within or very near the parent station's coverage area (a "fill-in") on the same channel or frequency are called booster stations. However, this can be tricky because it is possible to have both stations interfering with each other unless they are carefully designed. Interference can also be avoided by using exact atomic time obtained from GPS satellites to perfectly synchronise co-channel broadcast stations, as in a single-frequency network (SFN).
TV stations cannot have same-channel boosters due to video synchronization issues such as ghosting. AM stations do not have translators or boosters, though they are actually easier to create an SFN with.
Callsigns
Translator stations in the U.S. are given callsigns which begin with a W or K (respectively east or west of the Mississippi River, as with regular stations), followed by a channel number, and two serial letters for each channel. (The first station on that channel is AA, AB, AC, and so on.) Television channels are always two-digit, from 02 to 69; while FM radio channels are from 201 (88.1 MHz) to 300 (107.9 MHz), one every 0.2 MHz. (Example: W42BD, K263AF.) FM booster stations are given the full callsign (always including an -FM suffix, even if there is none assigned) of the parent station, plus a serial number, such as WXYZ-FM1, WXYZ-FM2, etc. LPTV stations may also choose a regular four-letter callsign with an -LP suffix, generally done only if the station originates programming.
In Canada and Mexico, all translator and booster stations are given the callsign of the parent station plus a serial number, such as XHABC and XHABC1, XHABC2, or CFON and CFON1, CFON2, etcetera, with no suffix.
Controversy
Some feel that the FCC has allowed certain noncommercial broadcasters to seriously abuse FM repeaters by allowing satellite-delivered programming extremely far outside the parent station's coverage area. Some religious outlets, such as Calvary Chapel of Twin Falls, Idaho, operate dozens or even hundreds of FM "translator" stations across the U.S. This often angers those who then cannot get even one LPFM station on the air because of one or more of those stations eliminating any available channels in an area. Many feel that this is a major abuse of process.