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avalon65
17-09-21, 18:51
From many years ago, I have a basic understanding of modulation as an ex Radio Ham. That was for voice transmissions and receiving.

What do , for example, x8 demodulators for a satellite signal . Googling tells me roughly that they multiply the signal.

I would appreciate a bit of basic information on this if possible.
Huevos
17-09-21, 20:47
The job of any demodulator is to recover the information content from the carrier... so for AM/FM the demodulator recovers the analogue audio content from the carrier... In the case of DVB-S/S2 the modulation is PSK (Phase-Shift Keying) and the demodulator returns binary digits, which go through error correction and are finally converted digital packets. One demodulator is needed per tuned frequency.

DVB can either be monoplex (normally feeds) or multiplex (which means a group of channels is combined and packed onto one single frequency). Also packed on the same carrier is program synopsis and TV program guide.
birdman
18-09-21, 01:51
Have a look at things like this:

https://www.open.edu/openlearn/science-maths-technology/exploring-communications-technology/content-section-1.7The theory is best explained by complex numbers (hence it looks like an Argand diagram) as tit's phase-based.
Huevos
18-09-21, 11:18
Have a look at things like this:

https://www.open.edu/openlearn/science-maths-technology/exploring-communications-technology/content-section-1.7The theory is best explained by complex numbers (hence it looks like an Argand diagram) as tit's phase-based.Except QAM is not used for satellite, it is used for cable and terrestrial. Satellite is almost always QPSK, 8PSK or sometimes APSK.
birdman
18-09-21, 12:41
Except QAM is not used for satellite, it is used for cable and terrestrial. Satellite is almost always QPSK, 8PSK or sometimes APSK.

OK, so try the Wkipedia entry:

https://en.wikipedia.org/wiki/Phase-shift_keying#Quadrature_phase-shift_keying_(QPSK)or

https://core.ac.uk/download/pdf/61800941.pdf

There are many results for a QPSK search.
avalon65
18-09-21, 12:50
@Heuvos:
yes I can recall monoplex and multiplex particularly with bulletin board servers.

@birdman:
Thanks for the links and some of the information there takes me back a good few years.

Thanks to both of you.