This stereo encoder produces an excellent crystal clear stereo sound and very good channel separation that can match with many more expensive stereo encoders that are available on the market.
The stereo encoder consists of three main stages; pre-emphasis, digital encoder and mixer stages.
Pre-emphasis stage is achieved by using two 47K resistors and two 1nF capacitors. This helps to eliminate the noise that is produced during the FM transmission of your audio signal.
Second stage that is built around NJM2035 is a digital encoder. All of its internal blocks except for two audio amplifiers (pins 1 & 14) that act as separators are created using digital circuits. The first digital circuit is a 38KHz oscillator that is generated by using external 38KHz crystal (pin 7), 10pF capacitor (pin 6) and 100pF bypass capacitor (pin 5). Once 38KHz frequency is generated it is then buffered and divided into two 19KHz signals with a phase difference of 180 degrees. Once that is done these two frequencies are connected with two time division MPX digital alternating switchers ,one for each audio channel. Here audio channels are switched between each other with a total frequency of 38KHz. If you would be able to slow this frequency to 1Hz per second you would be able to hear that this all but a trick. During the first half of the second you would hear the left audio channel and during the second half of the second you would hear the right audio channel. Due to the fact that the channels are switched with a fast frequency of 38KHz per second our brain is unable to recognize that these channels are really switched and receives this as a continuous audio signal. At the same time another signal from the 38KHz oscillator is divided by half into 19KHz. This signal is called a PILOT tone because it will help a stereo decoder on the receiver’s part to slice the MULTIPLEX signal (mixed L and R audio channels) and separate them back into left and right audio channels.
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