Promax PROLINK-4/4C Premium Manual De Instrucciones página 180

4) Spectral Inv. (spectral inversion)
This option enables spectral inversion to be applied to the input signal, though in
the majority of cases it should be in the OFF position (not inversion).
5) Attenuator
It permits to select attenuation between 0, 20 and 40 dB. It is advisable to activate
the 40 dB attenuator under that measurement conditions where the signal level is
near to the maximum input level (approximately starting from 20 dB under the
maximum level) and it is possible that the tuner becomes saturated. Under no-
saturation conditions, when increasing the attenuation value the BER measure
must to maintain or to increase (insufficient signal level) but never to decrease.
This configuration menu shows, besides the user definable COFDM signal
parameters, the value of the rest of COFDM signal parameters detected automatically:
Code Rate
Modulations
Hierarchy
Once you have defined the COFDM signal parameters, it will be possible to
measure the BER. When the BER measuring mode is selected, the monitor will show a
picture like the following:
Figure 15.- BER measuring screen for COFDM-modulated signals
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Also known as Viterbi ratio, defines the ratio between the data bits
number and the total number of bits transmitted (the difference
corresponds to the number of control bits for the error detection and
recovery).
Carriers modulation. It also defines the system noise immunity.
(QPSK, 16-QAM and 64-QAM).
The DVB-T norm contemplates the possibility to make a TDT
transmission with hierarchical levels, it is to say a simultaneous
transmission of the same program with different image qualities and
noise protection levels, in order the receiver can exchange to a
signal of smaller quality when the reception conditions are not
optimal.
USER'S MANUAL. PROLINK-4/4C Premium
06/2005