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Message: <blockquote data-quote="Old Satellite" data-source="post: 75321" data-attributes="member: 175277">Just to high light the FEC ( Forward error correction) is very important when you are at, or close to the systems capibility.The FEC (Forward Error Correction) indicates how many Bytes are used for the actual signal, and how many for correction of errors. A FEC of 1/2 means that 1 Byte out of 2 is used for error correction, while a ratio of 7/8 means 7 Bytes are used for the actual signal, and only one for error correction.A FEC of 1/2 gives as perfect as possible reception, since every Byte containing actual signal is controlled by another Byte checking it.When a provider chooses a FEC of 7/8 it means he is not wasting any bandwidth at the cost of delivering a signal. The lower amount of error correction means that more sophisticated equipment at the receiving end (for example a more stable and sensitive LNB, or higher reserves with the dish) are needed compared to the same transmission using a FEC of 1/2. So transmission data rate = customer information rate x 1/ (FEC rate).   FEC rate is typically in the range 1/2 to 7/8 so the transmission data rate is always significantly more than the customer information rate.   This is the actual formula:   SR = Symbol RateDR = Data Rate = the customer information rate.CRv = Viterbi  forward error correction (FEC) Code Rate.  Eg. 1/2, 2/3, 3/4, 5/6, 7/8 CRrs = Reed Soloman forward error correction (FEC) Code Rate. Eg. 188/204 m = modulation factor (transmission rate bits per symbol).   BPSK=1, QPSK=2, 8PSK=3 etc   Formula:   SR = DR / (m x CRv x CRrs)DVB-S Carrier bandwidthThe bandwidth of the carrier at the -3.8 dB points is approx the same as the symbol rate.The bandwidth of the carrier at the -12 dB points is approx 1.28 times the symbol rate.The occupied bandwidth, i.e. spacing between carriers is approx 1.35 times the symbol rate. For example: Symbol rate=27.5 Msym/s. Bandwidth = -1 dB 20.9 MHz, -2 dB 24.2 MHz, -3 dB 26.25 MHz, -3.8 dB 27.5 MHz, -4 dB 27.7 MHz, -6 dB 30.3 MHz, -12 dB 35 MHz.  in BriefIf the BBC were to move their 2D channels to a FEC of 1/2 then a lot more out of footprint customers would be much happier and could make do with smaller dishes as well.Kind RegardsOld Satellite</blockquote>

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