Promax HD Ranger + User Manual download pdf (Page 106)

2 March 2015

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DVB-T 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 received noise power. To measure it correctly

the channel should be tuned at its centre frequency.

MER

Modulation error ratio with 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 (VBER/CBER)

It is the system error rate. In a system of digital terrestrial signal

reception, after the COFDM decoder two methods of error correction are

applied. Each time an error correction is applied on the digital signal, the

error rate changes, so if the error rate is measured at the demodulator

output or after Viterbi or at the Reed-Solomon decoder output, different

error rates are obtained.

CBER

BER measurement for digital signal before the error correction (BER

before FEC).

VBER

BER measurement for digital signal after error correction (BER after

Viterbi).

In order to have a reference about the image quality, it is considered that

a system has good quality when it produces less than one un correctable

error per hour of transmission. This border is called QEF (Quasi-English

Error-Free,) and corresponds to one error rate after Viterbi equal to

2x10E-4, or 2 bit errors per 10.000.

This value is marked on the BER measurement bar after Viterbi. This the

BER for acceptable signals should be to the left of this mark.

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Promax HD Ranger + User Manual Page 106