[linux-dvb] Re: 8psk format

[Holger Waechtler]

Jeremy Hall wrote:

Hi,

Does anybody know what this 8psk format is?

8psk would be QAM8, QPSK would be QAM4 and BPSK would be called QAM2. The number describes the number of phase/amplitude transition states. Here some phase diagrams:

QPSK modulation:
(here each phase angle encodes a symbol out of 00, 01, 10, 11)

|
00 x | x 01
|
|
|
|
--------------------------
|
|
|
|
10 x | x 11
|


QAM16:
The 'real' QAM modulations use both angle and amplitude of the transmitted signal to encode a symbol:

0000 0001 | 0010 0011
x x | x x
|
|
0100 0101 | 0110 0011
x x | x x
|
--------------------------
|
|
x x | x x
1000 1001 | 1010 1011
|
|
x x | x x
1100 0101 | 1110 1111
|

So each of the 16 points in the phase/amplitude diagram above describes one binary symbol from 0...16. Since the mapping of points to symbols has to be defined somewhere the DVB standard defines a number of modulations, namely QPSK, QAM16, QAM32, QAM64, QAM128, QAM256.

DO any supported cards have the ability to lock to an 8psk transponder?

Some Demodulators support BPSK and an alternative QAM128 mapping. I suppose you have to read the datasheets to find out if any of them supports 8psk.

Holger




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