USER’S MANUAL. PRODIG-5
Page 58 11/2006
Viterbi synchronized
A digital carrier has been detected and the Viterbi algorithm is synchronized, but
too many frames arrive with non correctable errors. It is not possible to quantify
the BER.
MPEG-2
Correct detection of a MPEG-2 signal.
5.14.6 Digital TV: Measuring MER
Once determined the suitable parameters for COFDM, QAM or QPSK signal
reception, it will be possible to measure MER, press
[12] key until it appears the
MER measurement screen.
0 10 20 30 40
FREQ:
CH:
MPEG-2
NM: 8.4 dB
650.00 MHz
-3 kHz
43
C/N:
POWER:
» MER:
CBER:
VBER:
dB
dBµV
dB
>21.3
55.8
19.5
5.0E-4
5.3E-5
Figure 34.- MER measurement screen for DVB-T (COFDM) signals.
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.
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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