The BTSC Format
This system, selected by the EIA's Broadcast Television Committee, was
adopted by the FCC as the standard for stereo television transmission in 1984.
Sometimes known as MTS for Multichannel Television Sound, it is similar in
format to FM stereo but has the ability to carry 2 additional audio channels.
This is the Secondary Audio Program channel (SAP), sometimes used to carry
bilingual audio and a low fidelity audio channel for engineering purposes.
Left plus right mono information is transmitted the same way as in stereo
FM, maintaining compatibility with monaural, analog television receivers. A 15.734 kHz
pilot is used, instead of 19 kHz, which allows it to be phase-locked to the
horizontal line frequency. Also like FM stereo, a double sideband-supressed
carrier at twice the frequency of the pilot transmits the left minus right
stereo information. The stereo information is dbx encoded to aid in noise
reduction. The SAP channel is located at 5 times the pilot frequency. This FM
subcarrier carries mono; dbx encoded audio used for a second language or
independent program source. A professional audio channel may be added at 6.5
times the pilot frequency. This is a low fidelity FM subcarrier used for the
transmission of voice or data.
WA2FNQ-TV uses a Scientific Atlanta model 6380 stereo encoder/subcarrier
generator to transmit BTSC stereo. The left/right channels carry the program
audio while the SAP channel carries the 2-meter co-ordination frequency audio.
There is no professional channel.
The Scientific Atlanta Model 6830 Stereo/SAP Generator
The BTSC Signal