hi fi stereo multiplexer for fm

  
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A Left and Right source of audio are first pre-emphasized (HPF) and then fed to adder circuits. The output of one adder is the sum of the two signals, or the L + R signal (the monaural signal), and the output of the other adder is the difference of the two signals, or L R. The L R signal is applied to a balanced modulator along with a 38-k
hi fi stereo multiplexer for fm - schematic

Hz signal. The output of the balanced modulator is a DSBSC AM signal centered at 38 kHz. A portion of the 38-kHz signal is divided in frequency to become 19 kHz, and all three signals are applied to a summary/adder circuit at the output of the generator. The L + R signal, which contains baseband frequencies from near 0 Hz to 15 kHz, occupies that portion of the frequency spectrum. The 19-kHz tone is pilot sub-carrier signal, which will be used at the receiver to aid in the demodulation of the received signal. The L R signal, which has been DSBSC amplitude modulated by a 38-kHz tone, occupies the frequency range from 23 to 53 kHz. In FM, the noise increases with modulation frequency. To compensate for this effect, FM communication systems have incorporated a noise-combating system of pre-emphasis and de-emphasis. Pre-emphasis provides increased amplitude to the higher modulating frequencies prior to modulation under a well-defined pre-emphasis (high-pass filter) curve. This added amplitude will serve to make the higher frequencies more immune to noise by increasing their index of modulation. De-emphasis is just the opposite operation (using a low-pass filter) and it is done at the receiver. The NJM2035 is an integrated circuit used to generate a stereo composite signal and obtain switching out and 19Khz pilot signal due two input audio signal and 38Khz X-tal and few external CR. This stereo encoder is the perfect solution...



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