Promax US TV EXPLORER II Manual De Uso página 64

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).
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).
With the aim to have a reference about the signal quality, it is considered that a
system has a good quality when it decodes less than one non-correctable error for
every transmission hour. This border is known as QEF (Quasi-Error-Free) and it
corresponds approximately to a BER before FEC of 2.0E-4 BER (2.0x10
two incorrect bits of every 10,000). This value is marked on the measurement bar of the
BER and therefore, BER for acceptable signals must be at the left side of this mark.
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.
For the purpose of having a reference in the quality of an image, the system
quality is considered acceptable when It has less than one no-correctable error during
an hour of transmission. This limit is called TOV and its approximately rate is 3*10E-6.
This value has been indicated in the BER toolbar measurement. Therefore, an
acceptable measure of the BER must be on the left of this limit in the BER toolbar.
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.
Page 56
Figure 34.- Digital reception system via cable.
USER'S MANUAL. US TV EXPLORER II
-4
, that is to say
11/2013