Method and system for detecting signal modes in a broadcast audio transmission

摘要

A Japanese BTSC audio broadcast signal has three modes of transmission: mono, stereo, or dual mono. The control channel centering at 3.5 fH is one of the three channels in the J-BTSC signal, and contains information to indicate to the decoder which one of the three modes the audio transmission is in. The present invention uses a bandpass filter directly in the AM band, followed by envelope filtering and a decision circuit. Therefore, the need for AM demodulation and AM carrier detection is eliminated.