Atsc Signals - Promax US TV EXPLORER 2 User Manual

In a digital reception system for cable signals, after the QAM Annex-B
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
Annex-B decoder output. This is the reason because this screen provides the BER
measurement before FEC (Forward Error Correction).
TUNER A/D
Figure 31.- Digital reception system via cable.
The BER measurement is provided in scientific notation (i.e. 1.0 E-5 means
-5
1.0x10 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).
The BER measurement does not have any meaning if the input signal is a video
frame. This signal is useful only for laboratory purpose as long as the input signal is
generated by an ITU-T J.83/B generator using a PRN-23 pattern, reason why will not
work with a video frame.
If the input signal is like PRN-23 or a video signal, the BER measurement are
considered as acceptable when BER ≤ 3*10E-6 and therefore the MER value is taken
as reference measurement.
Below the BER analogue bar it is shown the tuned frequency (or channel) and the
frequency deviation in kHz between the tuned frequency and the one which optimizes
the BER (i.e. 800.00 MHz + 1.2 kHz). This deviation must be adjusted specially from the
C/N measurement in satellite band, by tuning again the channel in frequency mode
[24], to the lower reachable value.
5.14.7.2

ATSC signals

Once determined the parameters of 8-VSB signal, it will be possible to measure
BER.
In a reception system of terrestrial digital signal, after the 8-VSB decoder two
error correction methods are applied. Obviously, each time we apply an error corrector
to the digital signal, the error rate changes, therefore if we measure the error rate at the
output of the 8-VSB demodulator, at the output of the Viterbi decoder, and at the output
of the Reed-Solomon decoder, we obtain nothing more than different error rates. The
US TV EXPLORER II provides the BER after Viterbi (VBER).
Page 56
USER'S MANUAL. US TV EXPLORER II
BER before FEC
J.83/B QAM
REED-SOLOMON
DEMOD.
10/2007