dvb s2 introduce and basic terms related .pptx

It's to introduce basic concepts of dvb and related terms

1. 1 DVB-S Europe started in 1993. QPSK modulation method, maximum symbol rate 30 Mbaud /s, Audio and video use MPEG2 encoding The roll off coefficient is a fixed value , a=0.35 (BW= (1+a)* symbol rate) Inner code rate = (1/2, 2/3, ¾, 5/6 and 7/8) The ETSI standard is “EN 300421”

2. 2 DVB-S2 Backward compatible with DVB-S modulation is QPSK. Symbol rate for QPSK modulation is 45 Mbaud /s, and for 8PSK modulation the symbol rate is 30 Mbaud /s Variable roll-off coefficient a=0.35 or 0.25 or 0.2, which is more flexible and saves spectrum resources Video coding extension supports MPEG4, MPEG4AVC (H264) I nner code rate = (1/4, 1/3, 2/5, ½, 3/5, 2/3, ¾, 4/5, 5/6, 8/9, 9/10) ETSI standard is “EN 302307”

3. 3 Downlink Frequency Ku Band 10700Mhz ~ 12750 Mhz C Band 3400Mhz ~ 4200 Mhz The working frequency of the receivers is 950Mhz ~ 2150 Mhz Receiver Operating frequency

4. 4 LNB- local Oscillator frequency (1) After the satellite signal is down converted through the LNB on the satellite receiving dish, the frequency is reduced to the range of 950-2150 Mhz , so that the receiver can work normally Local oscillator frequency : the high frequency signal generated by local oscillator is mixed with the received high frequency signal to produced a difference signal. Its called intermediate frequency (IF) HIGH LO and LOW LO : When the local oscillator frequency is higher than the signal frequency (the local oscillator frequency is one intermediate higher frequency higher than the signal frequency), its called high local oscillator and when local oscillator frequency s lower than the signal frequency (the local oscillator frequency is one intermediate lower than the signal frequency ), its called low local oscillator . Since it is not easy to make local oscillator frequency very high, there are many high frequency heads in Ku band C band tuners mostly use a high local oscillator

5. 5 LNB- local Oscillator frequency (2) Comparing the high local oscillator and the low local oscillator, the high local oscillator has stronger anti interference ability. In addition, the C band and communication band are shared and more susceptible to interference, while the Ku-Band is a frequency band dedicated to satellite radio and television and has relatively less interference. Therefore, in the Ku frequency band, the frequency received by TV = downlink frequency of the satellite – local oscillator frequency of the LNB C-Band frequency received by TV = Local oscillator frequency of LNB- downlink frequency of satellite Common Local oscillator frequencies on the market include 9.75 Ghz, 10.6 Ghz, 10.75 Ghz, 11.25 Ghz, 11.3 Ghz etc.

6. 6 22K Switch A single Local oscillator frequency cannot cover full frequency band of Ku /C such as Ku frequency band 10700Mhz-12750Mhz and bandwidth of 2050 Mhz , which far exceeds frequency range of receiver IF frequency 950-2150Mhz Examples : The local Oscillator frequency is 9750Mhz, then adding the lower limit of intermediate frequency 950+9750=10700mhz plus the upper limit of intermediate frequency 2150+9750=11900Mhz, it cannot cover the 11900Mhz-12750 frequency range The Ku band is divided into two sections, namely : 10700Mhz -11900Mhz; 11550Mhz-12750Mhz, the high and low dual local oscillator frequencies 9750Mhz and 10600Mhz are used to cover the entire Ku frequency band, and the 22K pulse signal is used to control the frequency between the two local oscillator of the dual local oscillator LNB switch

7. 7 22K Switch (2) The 22K switch has two input interface and one output interface. In the 22K switch there is a 22khz frequency selection network circuit which can detect weather there are 22K pulses in the coaxial cable connected to the receiver, therefore controlling the two input interfaces on and off. The two input interfaces connected to an LNB with two antennas or two LNBs with a double star. The interface on (or 22K) corresponds to 22K pulse on and interface OFF (or 0) corresponds to 22K off