Promax HD Ranger Lite, User Manual

Page: 132 / 184

6 July 2015
2
DVB-S Measurements
Power
Measured power over the entire bandwidth of the channel.
C/N
Carrier/Noise ratio where C is the received power of the modulated carrier
signal and N is the noise power received. To measure it correctly the
channel should be tuned at its centre frequency.
MER
Modulation Error ratio with indication of Link Margin (LM). The link margin
indicates the safety margin respect to the MER level, measured for the
degradation of the signal up to the QEF (Quasi Error Free) value. MER
represents the ratio between the average power of the DVB signal and the
average noise power of the signal constellation.
BER (CBER/VBER)
It is the error rate. There are two measurements related to BER:
CBER (Channel Bit Error Rate):
BER of the signal after the QPSK demodulator and before applying the
error correction or FEC (Forward Error Correction).
VBER (Viterbi Bit Error Rate):
Measurement of the BER for the digital signal after error correction
(BER after Viterbi).
In a system for receiving digital satellite signals (DVB-S) after the QPSK
decoder two methods of error correction are applied. Each time an error
correction is applied on a digital signal its error rate changes, so if we
measure the error rate at the output of the QPSK demodulator or after
Viterbi or after the Reed-Solomon output decoder, the error rates
obtained are different.
PER
Measurement associated to VBER. It is an errored packet counter, plus a
total time counter, accounting for total packets lost over a given period of
time. In DVB-S, CBER is not to measure when PER is evaluated.