Studio transmitter link

A studio-transmitter link (or STL) sends a radio station's or television station's audio and video from the broadcast studio to a transmitter in another location.

This is often necessary because the best locations for an antenna are on top of a mountain, where a much shorter tower is required, but where a studio is completely impractical. Even in flat regions, the center of the station's allowed coverage area may not be near the studio location or within a populated area where a transmitter would be frowned upon by the community, so the antenna must be placed several miles or kilometres away.

Depending on the locations that must be connected, a station may choose either a point to point (PTP) link on another special radio frequency, or a newer all-digital wired link via a dedicated T1 or E1 (or larger-capacity) line. Radio links can also be digital, or the older analog type, or a hybrid of the two. Even on older all-analog systems, multiple audio and data channels can be sent using subcarriers.

Stations that employ an STL usually also have a transmitter-studio link (TSL) to return telemetry information. Both the STL and TSL are considered broadcast auxiliary services (BAS).

Aural telecommunication

Aural broadcasting refers to the audio part of the television (or microwave, radio, etc) transmission as opposed to the visual part of the broadcast signal. Television stations often distinguish between their power output as "visual power" and "aural power". For example, a local channel may state their visual power as 5500 watts and their aural power as 2900 watts (visual always being larger for such channels).

The FCC separates aural broadcasting into classes. For example, in the area of auxiliary broacasting, there are three classes of services:

• Aural broadcast STL station. A fixed station for the transmission of aural program material between the studio and the transmitter of a broadcasting station other than an international broadcasting station.
• Aural broadcast intercity relay station. A fixed station for the transmission of aural program material between radio broadcast stations.
• Aural broadcast microwave booster station. A fixed station in the broadcast auxiliary service that receives and amplifies signals of an aural broadcast STL or intercity relay station and retransmits them on the same frequency.

References

• CFR Title 47: Telecommunication PART 74—EXPERIMENTAL RADIO, AUXILIARY, SPECIAL BROADCAST AND OTHER PROGRAM DISTRIBUTIONAL SERVICES
• CFR Title 47: Telecommunication CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION SUBCHAPTER C-- PART 73-BROADCAST RADIO SERVICES