Satellite TV set-top box

Basic introduction

Definition

For satellite TV set-top boxes, there is no standard definition. Broadly speaking, any network terminal equipment connected to the installation of satellite TV can be used. Call it a set-top box. From analog channel supplements and analog channel decoders based on cable television networks in the past, to "Villas" Internet set-top boxes that connect telephone lines with TV sets, and integrated receiver decoders (IRDs) for digital satellites (IRD) , Digital terrestrial set-top boxes and cable TV digital set-top boxes can all be called set-top boxes. In a narrow sense, if you only talk about digital equipment, set-top boxes can be divided into Internet set-top boxes, digital satellite set-top boxes (DVB-S), digital terrestrial set-top boxes (DVB-T), and cable TV digital set-top boxes (DVB-C) according to their main functions. And the latest IPTV set-top boxes, etc.

Function

The basic function of a satellite TV set-top box is to receive and install satellite TV broadcast programs, and it has all broadcasting and interactive multimedia application functions, such as:

( 1) Electronic Program Guide (EPG). Provide users with an easy-to-use, friendly interface, and a way to quickly access the programs they want to watch. Through this function, users can see the TV programs that will be broadcast on one or more channels or even all channels;

(2) High-speed data broadcasting. It can provide users with various news such as stock market quotations, ticket information, electronic newspapers, popular websites, etc.;

(3) Online software upgrades. Online software upgrade can be regarded as one of the applications of data broadcasting. The data broadcast server broadcasts the upgraded software according to the DVB data broadcast standard. The set-top box can recognize the version number of the software, receive the software when the version is different, and update the software stored in the memory;

( 4) Internet access and e-mail. The digital set-top box can easily realize the Internet access function through the built-in satellite TV cable modem. Users can go online and send emails by installing a browser built into a satellite TV set-top box. At the same time, the set-top box can also provide various interfaces to connect to the PC, and use the PC to connect to the Internet.

Main parameters

Tuner/Tuner

Input frequency 950~2150MHZ

Input signal level -25dBm~-65dBm (75Ω)

Tuner power supply 13/18V

Decoding format MPEG2 MP@ML

Output standard NTSC/PAL

Output Port S-VHS RCA

Image resolution 720×576 (PAL) 720×480 (NTSC)

Output level 1Vp-p

Decoding format MPEG2 (Layer 1, 2)

Frequency response 20Hz~20KHz

Sampling frequency 32/44.1/48KHz

Adjustable output level (600Ω unbalanced)< /p>

Working voltage AC: 90~250V 50/60Hz

Power consumption is about 15W

Working environment 0℃~+40℃

Relative Humidity 10%~90%

The difference between extreme vibration

Overview of the difference

The difference between the dual polarization of the tuner and the dual local oscillator

Dual polarization, vertical and horizontal can be received, dual local oscillator, which means that two receiving tuner can be connected. The programs received by each other do not affect each other. If it is a tuner with a single local oscillator, the two machines can only watch one polarized program at the same time. What is a dual local oscillator tuner?

The main product varieties of tuner are: C/Ku band single local oscillator single polarization tuner, single local oscillator dual polarization tuner, dual local oscillator dual polarization tuner, etc. Kind of type. The dual local oscillator tuner means that there are two local oscillator frequencies in the tuner.

Ku frequency head

The frequency range of Ku band is 10.5～12.75GHz, and the bandwidth exceeds 2000M Hz, which is beyond the frequency range of the receiver. In order to achieve full-band reception, the Ku dual local oscillator tuner divides the Ku band frequency into high and low bands, namely 10.7～11.8GHz and 11.7～12.75GHz. The corresponding dual local oscillator frequencies are 9.75GHz and 10.6GHz respectively. The work of the two local oscillators is switched by the 0/22kHz switch, and only one of the two local oscillators is always working, so that the entire Ku-band frequency can be converted to the receiver. It can receive in the 950～2150M Hz intermediate frequency range.

Band frequency head

The dual local oscillators of the C-band dual local oscillator tuner work at the same time and do not need to be switched. The horizontally polarized probe and the vertically polarized probe in the tuner are respectively connected to a local oscillator. The received dual-polarized signal enters two local oscillators respectively. For example, if the local oscillator corresponding to the horizontal signal is 5150M Hz, the output intermediate frequency is in the range of 950～1450M Hz; the local oscillator frequency corresponding to the vertical signal is 5750M Hz. The output intermediate frequency is 1 550 ~ 2 050M Hz. If the tuner is rotated 90°, the intermediate frequency of the two local oscillators of the tuner is just the opposite. In this way, the dual-polarized C-band signal in the range of 3.7 ~ 4.2 GHz can be converted into an intermediate frequency signal of 950 ~ 2050 MHz and output at the same time, without the need for 0/22kHz or 13/17V switching. The purpose of this is mainly for the convenience of engineering use, because there is no need to use a dual-polarized feed and two high-frequency heads, only one cable (also has dual cables) can output horizontal and vertical dual-polarized signals at the same time . The prerequisite for using this kind of tuner is: the IF bandwidth of the receiver must be within the range of 950～2050M Hz to ensure that the program is not missed. Using this kind of tuner, for analog satellite TV receivers, as long as the receiver band is wide enough, regardless of whether there is a dual-polarization switching function, it can receive dual-polarization signals, which is not available in the early days. It is very suitable for machines with 13V/17V exchange functions. However, it is more troublesome for satellite digital TV receivers, because the dual local oscillators work at the same time, so we must first figure out the respective local oscillator frequencies of the two polarization directions, such as connecting the horizontal polarization signal to the low local oscillator 5 150M Hz, The vertical polarization signal is connected to the high local oscillator of 5750M Hz (of course, the reverse is also possible, as long as the tuner is rotated 90°), and then when setting the receiver parameters, please pay attention to set the horizontal signal local oscillator at 5 150M Hz, the local oscillator of the vertical signal The frequency is set at 5 750M Hz. As for the polarization mode in the parameters, it can be set arbitrarily, which has no effect on the reception, so that the dual polarization signals can be collected.