What are Digital TV Receivers?

A satellite television receiver is a device that receives satellite television signals. Usually refers to the indoor unit of a satellite TV receiving station, which consists of a second downconverter, channel selection, mid-band pass filter, main mid-amp, IF demodulation, and baseband processing circuit. Working process: The first intermediate frequency signal of 24 channels of 500 MHz bandwidth is sent to the second down-converter selection channel, and the output second intermediate frequency signal is sent to the intermediate frequency band pass filter, intermediate frequency amplifier and demodulator. The baseband signal is output, and after image processing and sound demodulation, the video and sound signals are output respectively and sent to the video and sound interface of the monitor to reproduce the image and sound; or VHF or UHF TV modulation built in the satellite TV receiver The RF output of the receiver is directly sent to the antenna socket of the home color TV receiver for people to watch satellite TV programs. ^[1]

Satellite television receiver

There are many types of satellite receivers, which can be divided into analog satellite receivers,

A basic satellite TV receiver should usually include the following parts: electronic tuning tuner,

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IRD's power-off memory function is very important for users. Easy

(1) Intuitive method: See if you can directly watch horizontal and vertical polarized satellite programs.

(2) Three-meter measurement method: Use a three-meter to check whether the voltage supplied by the IRD to the LNB can be changed; the required variation range: 12-20V. However, as long as there is a 14-18V switch, satellite programs with both horizontal and vertical polarization can be received.

When measurement conditions are not available, a comparison method can be used to determine the IRD demodulation threshold. the way is:

(1) Connect a detected IRD and an IRD to be tested to the power divider under the same antenna, and tune them to the same satellite program (with moving pictures and accompanying sound), and be in normal working condition .

(2) Slowly change the antenna

Receiving satellite programs has large clutter. The common reasons are:

(1) The receiving antenna is not aligned with the satellite, making the signal too weak. Should be adjusted left and right to find the best image with the least clutter, and then move up and down to fix the position without clutter.

(2)

1. Selection of antenna caliber. In rainy places, the limit caliber when watching a certain program can be increased by about 40% to reduce the impact of rain attenuation.

2. The antenna should be placed as hard as possible in the rain.

3. The antenna should take appropriate waterproof measures, such as

The so-called conditional access system CAS (Conditional Access System) refers to the transmission of a suitable control word CW (Control Word) to the descrambling terminal to control the entire

Authorization management is to enable authorized users who have paid the viewing fees in accordance with regulations to see the corresponding TV programs, but users who are not authorized cannot watch them, especially to prevent the illegal production of decoders, and to prevent unauthorized persons from deciphering and descrambling information. Look.

What are the options for conditional access?

Manual charging method (passive).

Automatic charging method (active):

I. Scrambling / descrambling methods:

1. Not addressed (decryption stick); | Baseband Processing | Digital Compression

2. Addressing (Authorized) Analog | Amplitude Processing Digital | Random Signal

3 Smart Card, IC Card (Front-end Center Authorization) | Time Base Processing | Password Mode

Second, no scrambling method:

1. Addressing is off. A. Some channels are off. B. All channels are off.

2. Addressing end scramble (end center authorization).

The terms "scramble" and "encryption" both perform cryptographic processing on data streams, but these are two different concepts and should be distinguished.

Scrambling is to change the characteristics of standard television signals to prevent unauthorized persons from receiving clear images and sound. This change should be in

DVB-S refers to satellite digital video broadcasting;

DVB-T refers to terrestrial digital video broadcasting;

DVB-C refers to cable digital video broadcasting.

The CA machine refers to a receiver that directly inserts a video card, and therefore cannot convert an encryption format, and is only applicable to an encryption system. Such as Imperial 901, Yum 3900, Tongzhou 2000E and so on.

The CI machine refers to a receiver that converts an encryption format through a module (CAM) and then inserts a viewing card, and is suitable for a variety of encryption systems. Such as Strong4355, Tigaton 611S series and so on.

AllCAM is a module for a variety of encryption systems. It is directly connected to the main board of the machine and an external card reader. It is mostly used for older machines, such as the module used on the popular 9500S.

MagicCAM and FreeCam are also modules for a variety of encryption systems. They are connected to the machine through slots and are mostly used for CI machines.

As AllCam, MagicCam and other modules can be compatible with multiple systems, the viewing card used must also be able to support multiple systems. Common FunXin1 files are card write files for 8515 cards, and DS9 are card write files for 876. They usually consist of two files, a system file and a data file.

Analog: It is a continuously variable signal, such as human voice, music, and television images. Early satellite communication systems were basically analog signals that were transmitted.

Apogee: A point in the ellipse orbit of a satellite furthest from Earth. When launching, a synchronous earth satellite orbiting the earth in a circular orbit is first sent into an elliptical orbit at a distance of 35,888 kilometers, and then a small booster rocket on the satellite is ignited. With the thrust of this rocket, the satellite enters It has been running on a circular track of 35,888 kilometers.

ATM (Asynchronous Transfer Mode): Asynchronous transfer mode is a method used in broadband digital networks to transmit information between devices in units of cells. The cell carrier can carry any type of information (such as video, voice, image and other multimedia data), and can operate at high speed. Establish a connection between the source and destination devices through the ATM switch. When the connection is established, any communication between the devices is possible.

Attenuation: The process of reducing the input signal level to avoid overloading the receiver. An attenuator is a passive device that is usually placed between a satellite receiver and a coaxial cable. In the differential television system, those users who are close to the differential station often use attenuators to reduce excessive signal levels.

Azimuth (AZ): Azimuth, an angle that a parabolic antenna of a satellite ground station must rotate in the horizontal direction when tracking a geosynchronous satellite. For any ground station, as long as the longitude of the geostationary satellite being tracked is known, the azimuth of its antenna should be determined.

BB (Base Band): Baseband, 6MHz bandwidth signal output by TV camera, satellite TV receiver or video recorder. Only the monitor can display the baseband signal.

Beta Format: Beta format, Beta system is a home video recording mechanism developed by Sony Corporation. This format is not compatible with the VHS format.

Bird Sat: A typical communications satellite that weighs several thousand pounds and has an average service life of seven years. It usually "parks" in a circular orbit at an altitude of 35,888 kilometers from Earth. The role of a communications satellite appears to be an electronic reflector that relays telephone, television, and data signals sent by various ground communications networks and ground stations, and transmits these signals to the corresponding satellite ground stations.

bit rate: Bit rate, the bit rate / code rate of the compressed code stream transmitted from the channel to the input of the decoder.

Blanking Frame interval In conventional television signals, 25 still images or 25 frames of images are transmitted per second. Frame interval time refers to the time interval between the end of one frame of image and the appearance of the next frame of image. With this interval, some data signals can be transmitted, but ordinary televisions cannot receive these data signals.

BNC Connector: BNC connector standardized small bayonet coaxial cable connector.

C / N (Carrier / Noise) Carrier-to-noise ratio The ratio of the satellite signal power to the receiver's noise power (in dB). The larger the ratio, the better the TV image quality. When the C / N is lower than 7dB, the quality of the TV image is very bad. When the C / N value is higher than 11dB, the image quality is excellent.

Carrier The center frequency of a signal transmitted by a radio or television transmitter. The carrier is usually AM or FM. In analog satellite television, the carrier is frequency modulated to transmit image signals and sound.

Carrier Frequency The operating frequency of a radio, television or microwave transmitter. The working frequency of AM broadcasting is from 535 ~ 1600KHz. The working frequency band of FM broadcasting is from 88 to 108 MHz. The transmission frequency of terrestrial television stations is from 54-890MHz. Microwave and satellite communication system transmitters work from 1 to 14GHz.

Cassegrain Antenna Cassegrain Antenna (ie, feed-back antenna) An antenna commonly used in satellite TV reception. The antenna's unique secondary reflection structure makes it not only eliminate the huge feeder bracket, but also retain the long focal length and high gain. advantage.

CATV Converter In the cable TV system, a special device connected between the TV and the cable. It replaces the TV tuner and enables users to freely choose the TV programs of each channel transmitted by the cable.

The C-Band C-band frequency ranges from 3.7 to 4.2 GHz, and is used as a frequency band for downlink transmission signals of communication satellites.

The term CDTV (conventional definition television) is used to refer to the analog NTSC television system proposed by ITU-R470.

Channel A band in which a particular signal is transmitted.

I / O interface

Chrominance (chroma) color information

Circular polarization International communications satellites use circularly polarized antennas to transmit signals to the ground in a spiral form. Some communication satellites transmit two different signals on the same frequency by left and right spirals, thus doubling the channel capacity of the satellite.

Satellite TV receiver input and output interface

1.Signal input

2.Signal loop output

3.RCA

4.YPbPr

5.S-VIDEO

6.SPDIF

7.USB

8.Network interface