What is Digital Satellite Television
Some observations on the afforementioned diagram:
DAC = Digital-to-analogue
video encoder typically contains 4 or more DACs which run at video rates
& quality. This infers 8 bit video DAC's (not cheap). 3 are needed for
RGB; another is needed for composite video out (PAL or SECAM). Some
use 10 bit DAC's & the difference *may* be visible by viewing sharp
transitions like black to white -hint : have a look at the On Screen
Display if you want to try to spot this effect. I have not included
the conditional access module for simplicity.
Complex IC's are needed for many of these blocks.
A qpsk demodulator/ADC/Viterbi decoder can easily cost around $7-$13 in manufacturers volumes! The mpeg transport demultiplexer & decoders cost even more!I haven't included the CPU & memory (usually around 1-3Meg. is needed & some of this may be fast,expensive SRAM). Perhaps you can now see why the digital receivers cost a lot more than the analogue ones!!! It's worth noting that on Astra,a Network Information Table (NIT) is transmitted every 10 seconds on every DVB/mpeg transponder. The information sent includes the FEC,S/R,frequencies etc.
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