How to choose a modulator

Modulator is the most widely used equipment in CATV front-end reconstruction. The most commonly used devices in the system need as many set-top boxes as broadcast channels. There are two kinds of modulators, adjacent frequency modulator and isolated frequency modulator. The price and specifications of modulators in the market are also varied. Choosing high-quality modulator is directly related to the whole CATV front-end conversion system. Choose a modulator and try to buy a modulator with adjacent frequency design. It is more convenient to add channels later. At present, some modulators on the market can only achieve more than 20 or 40 channels, and more than 40 channels will cause interference. You know, it will take at least 10 to 20 years to buy a modulator for cable TV transformation. In order to ensure the safe operation of the system, it is recommended to use the intermediate frequency processing adjacent frequency modulator as well! In case it is troublesome to add more programs with the increase of hotel or enterprise scale in the future, pay attention to identification when purchasing.

The most basic function of modulator is to modulate the video and audio signals provided by signal sources (such as digital TV set-top box, satellite digital TV receiver, DVD player, computer, video camera, TV demodulator, etc.). ) into a stable high-frequency RF oscillation signal. Video is amplitude modulated and audio is frequency modulated. According to the different color TV formats in the world, there are three kinds of PAL modulator, NTSC modulator and SECAM modulator, and PAL-D modulator is adopted in China.

China's standard stipulates that the intermediate frequency of TV is 38MHz. At the same time, the audio signal is modulated on 6.5MHz subcarrier after pre-emphasis and buffer amplification, and the output of FM modulator is mixed with 38MHz intermediate frequency to generate 3 1.5MHz audio carrier, which is combined with 38MHz mirror intermediate frequency to form a composite intermediate frequency signal. The composite IF signal is filtered by IF SAW to remove a sideband and become a residual sideband, and then another unnecessary 44.5MHz audio signal (i.e.

38 MHz+6.5 MHz)； At the same time, all unnecessary stray signals outside the frequency band should be suppressed below-60dB to ensure that there are no stray signals in this channel that interfere with other channels.