So, what is a set-top box? The personage said, set-top box is installed on the top of the TV set on a box, technically speaking, is to extend the function of the TV set of a home appliance, which is divided into analog TV set-top box and digital TV set-top box according to the different types of signals received. Analog TV set-top boxes can only receive analog signals, and digital TV set-top boxes due to close contact with the TV set, and is a digital device, and therefore is the true meaning of the set-top box. At present, the general public commonly used in the family of ordinary television sets only need to install set-top boxes, you can watch digital television, without the need for the original cable TV lines and television sets to make any changes.
To update you a concept first, now the so-called digital TV is not the true meaning of digital TV. Digital TV has to satisfy the digitalization of the program source transmission and the digitalization of the receiving TV interface, that is, the DVI interface. Now the set-top box only provides the S port or AV interface, not to talk about what digital TV. Of course, in the computer with a TV card can indeed watch TV, but the display of the movie effect than the TV is much worse ... to watch real digital TV can only rely on their own, with a computer as a source, from the Internet under some 720p or 1080i film with a graphics card to the TV, whether S or VGA or DVI, than the damn digital TV strong old, I am! Qingdao, which has been all on the so-called digital TV, hey, through the concept of ah!
"Analog to digital", can bring what benefits to the user?
It is understood that after the conversion to digital television, the user can watch the program, will increase from more than 40 sets to more than 70 sets, in addition to a number of pay-per-view channels. In addition to the massive increase in television programs, digital television transmission signal interference resistance, the clarity of the TV screen will also be greatly improved.
"Television from analog to digital, the changes brought about by the program is not only richer, clearer picture," due to the digital television using two-way information transmission technology, increasing the analog cable television can not be achieved interactive capabilities. In the cable digital TV this new platform, the past only for passive viewing of the TV, will be given many new functions.
For example, with the development of more value-added services based on the digital TV platform, the public can access a variety of network services through the TV, including video-on-demand, online shopping, distance learning, telemedicine, checking the records of drivers' violations, and even paying for water, electricity, and gas bills and so on, making the TV set a veritable information appliance.
No matter what level, users have the right to freely purchase set-top boxes. However, due to various reasons, the digital TV signals currently transmitted in various cities are different, and the set-top boxes purchased by the users themselves may not work properly because of the standardization problem. Therefore, before purchasing, users must find out whether the set-top box is compatible with the digital TV signals in the region.
Your local cable company produces various programs into a transport stream (that is, TS), which is scrambled and transmitted to you, and then descrambled and given to the set-top box, which contains a number of programs, that is, the channels we originally said, (if it really depends on the frequency of the different stations to choose, then, what some people said above the amplifier can be used, but cable digital TV is not like that). According to the program you choose to watch (channel), the demodulator (Tuner) in the set-top box from the TS to distinguish that station, according to that is sent, different stations have different PID codes, after distinguishing out, that way the program to the decoder chip to decode the audio and video streams, and finally through the two wires connected to the TV to be played on the TV. Of course, in the middle there is what channel compensation, demultiplexing and other specialized things I will not go into detail.
To use the amplifier, you can only amplify the decoded signal, that is, all TV only one channel, can not change the station, a change all have to change. If you want to amplify the pre-decoding signal, you can't do it technically, and even if you did, you'd have to get a set-top box for each TV to use for decoding, so it's not possible. And each set-top box has a CA card, called Conditional Access Card, encrypted, without this card, even if I send you a free set-top box, you can not watch, this card is equivalent to the role of the cell phone card, the cable operators around the use of the equipment is not the same, I am to give you the card you are not necessarily used. There is no way, or you find them to negotiate? If you don't, I can't help it, the hotel's TV fee should be differentiated from the family's, and the operator there is really not doing business.