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Satellite Systems - What to Buy - What to install
Dish Size for DVB-S / DVB-S2 / DVB-S2X
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<blockquote data-quote="Captain Jack" data-source="post: 892232" data-attributes="member: 243342"><p>This has been discussed when DVB-S2/8PSK first came into play as the requirement for a better signal quality became necessary. This knocked out a lot of "fringe reception" signals after a few channels changed modulation.</p><p></p><p>I am sure there is a complex mathematical formula to calculate the required signal level for a specific modulation and FEC rate. FEC is important here as the lower the FEC, the more signal you need. FEC rate of 1/2 needs 2.7dB C/N to lock in DVB-S QPSK modulation, whereas with 2/3 you would need 4.4dB and with 3/4 you would need 5.5dB C/N to lock with the same modulation. Some HD channels on Sky had FEC of 8/9 - this allowed them to squeeze higher bit rates into audio and video, as less of the bandwidth would be taken up by error correction. FEC of 1/2 means that 50% of packets are used for error correction, whereas FEC 8/9 means that only 11% of packets is used for error correction and the rest for audio/video.</p><p></p><p>If and when Sky decide to pump out UHD with new modulations, I am sure that they will somehow ensure that the millions dishes won't need to be upgraded to larger ones by playing with FEC and transponder strength. I believe each TP's power can be adjusted from the uplink site - could be wrong though.</p><p></p><p>Discuss.</p></blockquote><p></p>
[QUOTE="Captain Jack, post: 892232, member: 243342"] This has been discussed when DVB-S2/8PSK first came into play as the requirement for a better signal quality became necessary. This knocked out a lot of "fringe reception" signals after a few channels changed modulation. I am sure there is a complex mathematical formula to calculate the required signal level for a specific modulation and FEC rate. FEC is important here as the lower the FEC, the more signal you need. FEC rate of 1/2 needs 2.7dB C/N to lock in DVB-S QPSK modulation, whereas with 2/3 you would need 4.4dB and with 3/4 you would need 5.5dB C/N to lock with the same modulation. Some HD channels on Sky had FEC of 8/9 - this allowed them to squeeze higher bit rates into audio and video, as less of the bandwidth would be taken up by error correction. FEC of 1/2 means that 50% of packets are used for error correction, whereas FEC 8/9 means that only 11% of packets is used for error correction and the rest for audio/video. If and when Sky decide to pump out UHD with new modulations, I am sure that they will somehow ensure that the millions dishes won't need to be upgraded to larger ones by playing with FEC and transponder strength. I believe each TP's power can be adjusted from the uplink site - could be wrong though. Discuss. [/QUOTE]
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Satellite Systems - What to Buy - What to install
Dish Size for DVB-S / DVB-S2 / DVB-S2X
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