Promax TV EXPLORER HD+ Manual De Instrucciones página 189

USER'S MANUAL. TV EXPLORER HD+
Figure 43.- DVB-T/H (COFDM) signals MER measurement screen.
First of all, you will see the modulation error ratio measurement: MER.
Following, it appears the Noise Margin (NM) measurement (in the figure value
8.4 dB). It indicates a safety available margin according to the MER level measured that
allows signal degradation until arriving to the QEF (Quasi-Error-Free) limit value.
Figure 44.- DVB-S2 (QPSK/8PSK) signals MER measurement screen.
In the case of a DVB-S2 signal (QPSK/8PSK) instead of the Noise Margin (NM)
appears the measure of the Link Margin (LM); in the previous figure with a value of
2.3 dB. The LM is equivalent to the NM and indicates the distance to the QEF (generally
defined as one lost packet per hour). The LM is measured in dB and its value is equal to
the safety margin that separates us from the QEF. As bigger LM better signal quality. An
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 LM equal to 0 (zero) displays a service
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 (MER), used in digital systems is similar to the Signal/Noise
(S/N) ratio in analogue systems.
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