Constellation Diagram - Promax TV EXPLORER HD User Manual

TV EXPLORER HD / HD
USER'S MANUAL.
In the case of a
appears the measure of the
LM
2.3 dB. The is equivalent to the
defined as one lost packet per hour). The
the safety margin that separates us from the
LM
with a negative value means that there is no signal reception or errors are beginning
to display clearly in the video or the audio. An
and occasionally some artefacts can be observed.
Analogue and digital carriers are very different in terms of signal contents and
power distribution over the channel. They, therefore, need to be measured differently.
The modulation error ratio (
S/N
( ) ratio in analogue systems.
MER
represents the relation between the average power of
average power of noise present in the constellation of the signals.
When measuring
DVB-S2,
Link margin in
signal.
QAM 64
By example,
Though it is preferable to have at least a
possible degradation of the system. While
28 dB
greater than with margins of al least
seen in portable analysers is of approximately
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, of the digital symbols
recived over a period of time.
There are different types of constellation diagrams for the different modulation
TV EXPLORER
modes. With the
DVB-T/H DVB-C DVB-S
, ,
In the case of an ideal trnasmission 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.
10/2012
LE
DVB-S2 QPSK/8PSK
signal (
Link Margin LM
(
NM
and indicates the distance to the
LM
QEF
MER
), used in digital systems is similar to the Signal/Noise
MER,
it also shows the noise margin in
which indicates the distance from the
demodulators require a
3
3 dB
HD / HD
LE
DVB-S2
and signals.
) instead of the Noise Margin (
); in the previous figure with a value of
is measured in dB and its value is equal to
LM
. As bigger better signal quality. An
LM
equal to 0 (zero) displays a service
DVB
DVB-T
QEF
MER
greater than
4 dB
or margin to compensate for any
QAM 256
demodulators require a
. Normally, the maximum
34 dB
.
it is possible to display constellations for
NM
)
QEF
(generally
signal and the
C S
, , and the
point at the current
23 dB
to work.
MER
MER
value
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