ATSC/8VSB Measurements - Digital Video and Audio Broadcasting Technology - page 451

receiver calculates the signal-to-noise ratio (S/N ratio) in dB referenced to
the signal power, which is likewise calculated by the test receiver.
In the event of phase jitter, the lines in the decision fields of the constel-
lation diagram are trumpet-shaped, i.e. they become increasingly wider as
the distance from the horizontal center line increases (Fig. 24.5.).

Fig. 24.5. 8VSB constellation diagram revealing phase jitter

Q

Erro r
vect o r

Real
vector

Decision
border

Ide a l
vec t or

I

Fig. 24.6. Determining the MER of an 8VSB signal

The Modulation Error Ratio (MER) parameter summarizes all errors
that can be measured within a constellation diagram. For each type of error
(interference), an error vector is continually calculated. The sum of the
squares (RMS value) of all error vectors is calculated. The ratio of the er-
ror-vector RMS value and the signal amplitude yields the MER, which is