With the emergence of digital television, many manufacturers began to use modulator equipment. The role of the TV modulator is to convert standard audio and video signals into a TV channel that meets specific standards. Therefore, with the continuous development of the TV industry, many TV modulators are mostly used in cable TV systems.
The output signals of multiple TV modulators are mixed and can be transmitted to the desired place through a radio frequency coaxial cable. This is the prototype of the cable TV system. The cable TV system shown in the figure below can be formed by using the modulator as the transmission device and the transmission network.
The signal source is output by the AV signal generating device. The AV signal generation equipment can be any equipment that can output standard AV signals, such as * receivers, DVD players, cameras, computers with AV output functions, etc. Currently, digital receivers are the most used.
TV modulators are divided into standard type, adjacent frequency transmission type and frequency separation transmission type according to the output frequency characteristics. The standard type is usually used in relatively formal small TV stations and other facilities, and is not used much by the people; the adjacent frequency transmission type is mainly developed for cable TV systems. It has not been long since it was invented, and it has only been introduced into my country for more than ten years. In the construction process of analog cable TV in 2010, the amount of social ownership is not small; the characteristic of the frequency-interval transmission type is that all modulation products are output, and the original flavor is authentic. Of course, the audio-visual effect is almost the best.
If a conventional cable TV system is established, the modulator must be the adjacent frequency transmission type. Although the investment is large, the proportion of equipment in the computer room is not large in the entire cable TV system, let alone the adjacent frequency transmission type occupies the smallest spectrum resources, in the limited TV broadcast frequency band, it can accommodate more channels (about one hundred sets of TV programs can be transmitted). If it is not necessary to transmit the most TV channels, it can be transmitted at a lower frequency, which can effectively reduce transmission loss and facilitate coverage larger territory. This advantage of adjacent frequency transmission is particularly important in large-scale cable TV systems. Therefore, in the early construction of cable TV, county towns may choose the 750MHz system because the required coverage area is small, and provincial cities may choose the 750MHz system because the required coverage area is large. Choose 550MHz system or even 450MHz system more.
