Philips 14AA3322/40B Installationsanleitung PDF herunterladen (Seite 103)

Generation of a transport stream for DVB and realisation of a HF-modulated DVB-signal

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Figure 1.2: RFExpert System Monitor

Question1

What is the EVM?

The EVM is the Error Vector Module. It’s calculated from the MER. In fact, it’s the value of the module of

the vector that goes from the position of the ideal symbol received (at the I-Q plane) to the position of

the real received symbol (which differs from the original position because of the noise).

It’s measured in %RMS (Root Mean Square), and the lower it is, the better the signal is.

Question2

What is the Margin?

The margin that we see on the screen is the margin between the Signal-to-Noise value of the system and

the Signal-to-Noise leading to a Quasi-Error-Free point (BER=1.0E-4). It represents how far the MER is

from the QEF (Quasi Error Free).

The higher the margin is, the better the signal is.

Question3

Look at the error window (top right corner). What is the difference between PreFEC BER, PostFEC BER,

SER and ErrorSec?

The PreFEC BER is the bit error rate before any forward error correction. That’s why it is higher than the

PostFEC BER. The PostFEC BER is the bit error rate after all the correction codes, such as Reed Solomon.

The SER (Segment Error Ratio) is a numerical number that represents the errors that are measured in a

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Philips 14AA3322/40B Installationsanleitung Seite 103