Promax US TV EXPLORER II, User Manual

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USER’S MANUAL. US TV EXPLORER II
01/2008 Page 65
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There are different types of constellation diagrams for the different modulation
modes. With the US TV EXPLORER II it is possible to display constellations for DVB-S
and DVB-S2 e ITU-T 1.83/B signals.
In the case of an ideal transmission channel, free of noise and interferences, all
symbols are recognized 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 colors the density of hits and includes
zooming, scrolling and clearing functions for a better graph representation on screen.
5.15.1 ITU-T J.83/B (QAM-Annex B) signal
Go to the UTILITIES menu by pressing the [22] key, and then select the
CONSTELLATION option.
For example the modulation type: ITU-T J.83/B is showed on screen. Next, the
frequency and channel number corresponding to the channel plan selected as well as
the satellite downlink frequency. Finally, the satellite name and orbital position are
stated.
MODULATION:
F:
CH:
61
MHz 794.00
MPEG-2 ITU-T J.83/B CLEAR ZOOM:x1
DECAY: 16
Figure 45.- Constellation Diagram. MPEG-2 TS ITU-T J.83/B.