Service manual

Explanation BTSC Stereo System (USA)
The standard for TV stereo audio in the USA was set by the Broadcast Television
Systems Committee (BTSC). The BTSC system was designed to:
• be compatible with then current monaural TV receivers,
• present a good stereo separation and signal to noise ratio,
• make available a Second Audio Program as a separate audio channel,
• provide a technical voice/data channel to communicate within the TV stations
system.
In a transmitted TV signal in the USA, the FM Audio signal is placed 4.5 MHz above the
AM Video Carrier. The audio FM has a nominal deviation of +/-50 kHz. With the BTSC
system this signal separation and FM deviation is maintained.
Figure: Base band audio signal spectrum
Figure above shows the detected base band audio signal spectrum. The 'L+R' signal
maintains compatibility with the original (and current) monaural receivers. With Double
Sideband Suppressed Carrier (DSSC) for the 'L-R' signal, there is a need for an exact
re-insertion of the missing carrier. This to assure a good detection in the receiver. This
is the main purpose of the pilot carrier at 1fH (15,743 Hz). It also serves to alert the TV
set (and the customer) to the fact that the signal is in stereo. As the pilot is at the exact
horizontal scan frequency, this can lead to false indication from such sources as VCRs,
Signal Amplifiers, etc. where both sound and video are present with RF energy.