TV tuner is an important receiving terminal device, commonly known as high-frequency head. Ordinary TV tuner is analog manner to receive amplification, gating, frequency, figure sound demodulation process, if the distortion and distortion which will make the received pictures and associated audio quality deteriorated. Rear-Projection TVs are digital TV, analog TV signals to change the first digital signal compression, transmission, receiving, processing, storage, recording and control, digital TV receiver terminal by the first digital TV tuner for high-frequency amplification, compared handling , channel decoding and demodulation. And then back through the digital television receiver circuit source decoding out after treatment to restore the original image and sound, if the distortion occurs in which this process will result in error an error, if the tuner may be beyond the scope of regulation, they can not receive pictures and associated audio.

The digital tuner includes not only an important indicator of the original color TV, in the phase noise, non-linear indicators and detection methods such as the lockout time was different. Analog TV tuner to receive analog TV signals, it will be a number of different frequencies of high-frequency TV signal converted into a fixed IF output, complete the spectrum move. Digital TV tuner to receive digital broadcast television signals, not only to complete the analog tuner to be accomplished by moving the function of the spectrum, but also the completion of demodulation and channel decoding. As a front-end digital TV receiver, digital TV tuner with digital devices, so that in the production process than analog tuners, easy to assemble and adjust, reliability, and stability is greatly improved. Thus, digital TV tuner in technology and processes that there are many different from the analog TV tuner features, its performance is much better than analog TV tuner.

Currently on the market some of the rear-projection TV is only equipped with a tuner, even though it has a dual-window function can not receive both sets of TV programs. In other words, only a window to watch television programs, another window can only see DVD program or other external device input program. If you buy into the built-in two high-frequency head rear-projection TV, can be achieved simultaneously watch two TV channels, such as the realization of picture in picture function.

Classification of TV tuner

The entire digital TV tuner function of the circuit composed of two parts. As shown, the front-end tuning circuit, is responsible for RF reception, frequency conversion, filtering and automatic gain control and other functions, the part of the circuit in addition to the basic functions for signal reception, but also properly handle the signal interference problems, a common signal interference, such as mirror the temporary channel interference and other issues, analog TV interference will bring a number of map lines, while the number of serious interference with television signals can directly lead to the loss; back-end demodulation circuit, is responsible for A / D conversion, demodulation and error correction decoding and other functions.

How to identify good or bad video cable

User raise this question a lot, and some made a User works for several years, is still on this issue can not be a better grasp. This is a view, "no problem" but a very important practical engineering problems; the real test still requires specialized equipment and instruments. These apparatus and equipment design and engineering units is not available. The quality of project identification video cable I hope you draw on collective wisdom. Here to talk about a few points and attract valuable comments bar:
1) The visual appearance of identification: 1. PVC sheathing: The surface can be seen inside the Knitting regularly pressed the "roughness", indicates the processing technology is good, does not produce relative sliding, is good cable. Appearance of smooth, do not see Netting pressed the "roughness", Yong Shounie jacket with loose dynamic, really bad cable;
2) Check shield provision Net: Part number is enough? Copper Knitting, check the weldability, tinned copper wire scraping to see inside is not copper, aluminum-magnesium alloy wire significantly greater than the hardness of copper wire; Knitting sparse, evenly distributed, with the insulating layer is not wrapped tight and others are Poor cable;
3) Check cored wire: Diameter - SYV cable for the 0.78-0.8mm, SYWV cable 1.0mm; recently there has been a SYV75-5 Core wire diameter is 1.0mm cable, this cable characteristic impedance, certainly not 75 ohms, not applied to the 75 ohm transmission system;
4) check the core line and the insulating layers stick together: oblique incision insulating layer, by stripping the direction of pull-core line, look at the core line and the insulating layer there any dip All process materials; good cable has a larger stick together, and poor cable does not stick together;
5) Longitudinal tensile experiment: take a meter cables, cut open the core wire layer, insulation layer, shield layer, outside the household sets, each stay 10 cm long. Methods are: two hands grip the cable were adjacent two-story, to pull in the opposite direction; pull the power cables are generally not a good move, bad cable does not charge vigorously, you can easily pull out - a very important elevator cables that many so-called "Elevator cables" this problem exists;

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