S/N IMPROVING CIRCUIT FOR SUB BROADCAST IN FM MULTIPLEX RECEIVER

• Main Author: MATSUMOTO YASUKAZU
• Format: Patent
• Language: English
• Published: 18.10.1989
• Subjects: BROADCAST COMMUNICATION; ELECTRIC COMMUNICATION TECHNIQUE; ELECTRICITY; TRANSMISSION

PURPOSE:To improve the S/N of a sub broadcast without deteriorating the effect of a band pass filter by adding a difference signal of opposite phase to an FM composite signal comprising a main broadcast band and a sub broadcast band in a circuit extracting the sub broadcast so as to attenuate the difference signal of the FM multiplex signal. CONSTITUTION:A parallel circuit comprising a buffer 6 to adjust the level and a series circuit consisting of a multiplex circuit 7 and a balanced modulator 8 is formed between an RF IF detector 2 and a band pass filter 4 in a circuit extracting a sub broadcast. The multiplex circuit 7 extracts a difference signal (L-R) in opposite phase from a composite signal outputted from the RF IF detector 2, sends the result to the balanced modulator 8 and also extracts a subcarrier 38kHz and ends it to the balanced modulator 8, where the subcarrier 38kHz is modulated by the difference signal (L-R) in opposite phase and the result is fed to a composite signal subjected to level adjustment outputted from the buffer 8. As a result, the portion of the difference signal (L-R) of the sub channel in the composite signal inputted to the band pass filter 4 is sufficiently attenuated.