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The following figure shows that when making C/N measurements in the relative
method (∆F), it is essential to bear in mind the presence of adjacent channels;
otherwise, the noise could be confused with the signal of another channel.
Taking as example the previous figure, if we suppose that for the channels that
appear in the figure it has defined a bandwidth of 8 MHz, in the relative mode of
PROMAX-10
measurement the
Note that this method can cause erroneous measures in the measurement of the
channels D24 and D25.
For D24 it is advised to configure NOISE FREQ = -4.5 MHz and to verify if the
measurement increases. In case a channel has two adjacent channels (for example
channel D25) it is recommended to select the absolute mode and to assign to the
NOISE FREQ. parameter a frequency corresponding to a free channel (for example
between D26 and D27).
4.2.3.1.5
Constellation Diagram representation, Bit Error Rate (BER)
and Modulation Error Ratio (MER) measurement (only for
digital channels)
Once obtained the Power and C/N ratio measurement, the BER and MER
measurement on tuned channel as well as the Constellation Diagram graph
representation for the DVB-QAM digital signal can be obtained pressing the rotary selector
.
PROMAX-10
The
like the one of the attached figure. On it besides the Constellation diagram, also appears
the type of QAM modulation, the symbol rate (SR), the error rate obtained for the digital
signal (Post-BER measurement (BER after FEC) shown as BER ; Pre-BER
measurement (BER before FEC) shown as
measurement (MER), the represented quadrants and the type of detected codification.
Page 26
Figure 21.- Example of digital channels spectrum.
SE
will take as value for NOISE FREQ. = 4.5 MHz.
SE, after some seconds for calculation, will show a screen
USER'S MANUAL.
BER), the modulation error ratio
PROMAX-10
SE
07/2011
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