Broadband Coaxial Cable

The other kind of coaxial cable systems uses analog transmission on standard cable television cabling. These can be used for digital data transfer also. It is cabled broadband. Although the term “broadband” comes from the telephone world, where it refers to anything wider than 4 kHz, in the computer networking world “broadband cable” means any cable network using analog transmission.

Since broadband networks use standard cable television technology, the cables can be used up to 300 MHz (and often up to 450 MHz) and can run for nearly 100 km due to the analog signaling, which is much less critical than digital signaling. To transmit digital signals on an analog network, each interface must contain electronics to convert the outgoing bit stream to an analog signal, and the incoming analog signal to a bit stream. Depending on the type of these electronics 1 bps may occupy roughly 1 Hz of bandwidth. At higher frequencies, many bits per Hz are possible using advanced modulation techniques.

Broadband systems are divided up into multiple channels. Frequently the 6MHz channels are used for television broadcasting. Each channel can be used for analog television, CD-quality audio or a digital bit stream at, say 3 Mbps, independent of the others. Television and data can be mixed on one cable.