Promax US TV EXPLORER II, Руководство пользователя

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USER’S MANUAL. US TV EXPLORER II
01/2008 Page 57
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5.14.7.2 DVB-C signals
Once determined the parameters of QAM signal, it will be possible to measure
BER , press the [12] key until the BER measurement display appears.
In the BER measurement mode, the monitor will show a display like the following
one:
FREQ:
CH:
C/N:
POWER:
MER:
BER: »
16.5
66.2
24.7 dB
dBµV
dB MHz
kHz
650.00
-3
43
3.4 E-4
-6 -5 -4 -3 -2 -1
MPEG-2 TS
Figure 33 .- DVB-C ( QAM ) signals BER measurement screen.
The BER measurement before error correction is shown: BER before FEC
(Forward Error Correction).
In a digital reception system for cable signals, after the QAM demodulator an
error correction method called Reed-Solomon is applied (see following Figure).
Obviously, the error rate after the corrector is lower to the error rate at the QAM
decoder output. This is the reason because this screen provides the BER measurement
before FEC (Forward Error Correction).
Figure 34.- Digital reception system via cable.
The BER measurement is provided in scientific notation (i.e. 1.0 E-5 means
1.0x10
-5
that is to say one wrong bit of every 100,000) and through an analogue bar (as
its length is smaller the signal quality will be better). The analogue representation is
done on a logarithmic scale (not linear).