Constellation Diagram; Dvb-S/S2 (Qpsk/8Psk) Signals - Promax US TV EXPLORER 2 User Manual

USER'S MANUAL. US TV EXPLORER II
By example, 8-VSB demodulators require a MER greater than 15 dB to work.
Though it is preferable to have at least a 3 or 4 dB margin to compensate for any
possible degradation of the system. While QAM Annex-B 64 demodulators require a
MER greater than 21 dB or QAM Annex-B 256 greater than 28 dB with margins of at
least 3 dB. Normally, the maximum MER value seen in portable analysers is of
approximately 34 dB.
Finally it is shown a status line, which displays information about the detected
signal.
5.15

Constellation Diagram

The constellation diagram is a graphic representation, called I-Q, of the digital
symbols recived over a period of time.
There are different types of constellation diagrams for the different modulation
modes. With theUS TV EXPLORER II it is possible to display constellations for DVB-S
and DVB-S2 signals.
In the case of an ideal transmission channel, free of noise and interferences, all
symbols are recognised by the demodulator without mistakes. In this case, they are
represented in the constellation diagram as well defined points hitting in the same area
forming a clear dot.
Noise and impairments cause the demodulator to not always read the symbols
correctly. In this case the hits disperse and create different shapes that at the end will
allow to determine at a glance the type of noise in the signal
Every modulation type is represented differently. A QPSK signal is represented
on the screen by a total of four different zones and a 8PSK is represented by a total of
eight different zones and so on.
The constellation shows in different colours the density of hits and includes
zooming, scrolling and clearing functions for a better graph representation on screen.
5.15.1 DVB-S/S2 (QPSK/8PSK) signal
Go to the UTILITIES menu by pressing the
CONSTELLATION option.
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[22] key, and then select the
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