Principle

6 channels of voice, data and image signals are compressed, and transformed into 0-4kHz base band signals through channel coding, multiplexing and TCM modulating. The base band signals are modulated once into signals in range of 40~500kHz with 4kHz bandwidth through a series of processing by digital techniques, such as, high speed A/D conversion, mean-square wave-former, gradually over sampling, digitally filtering, self-adaptive equalization etc. The modulated signals are then delivered to high frequency cables through power amplifiers, band-pass filter and hybrid. Finally the signals are transmitted to the corresponding end by power lines.

The DT340 in corresponding end receives the signals transmitted through the power lines, and then converts them to 4kHz base band signals by hybrid, receiving filter, and demodulating. At last, the digital multiplexer reverts the signals to channel voice, data, and image signals.

Since 6 channels of signals are multiplexed in 0~4kHz, the data density in-band is very high (up to 28.8kbps). So, it is very important to transfer the base band signals to line frequency without any distortion. Adopting fully digital one-pass modulation technique can not only move base band signals to line frequency without any distortion, but also use digital check and error correction techniques during modulating, further enhancing the anti-disturbance capability of the signals. Fully digital one-pass demodulation can correctly work out the signals disturbed by the line noise.