Promax -10 Manual Del Usuario página 92

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.
Figure 19.- Example of digital channels spectrum.
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
measurement the PROMAX-10 will take as value for NOISE FREQ. = 4.5 MHz. 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 in 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
. ( See appendix H 'Principle of QAM modulation. The Constellation Diagram ').
The PROMAX-10, after some seconds for calculation, will show a screen 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 (BER), the modulation error ratio measurement (MER) ( see appendix G
'Measurement of the modulation digital ratio (MER) '), the represented quadrants (Q1-4)
and the type of detected codification (MPEG2).
When pressing again the rotary selector
new measurement. If the selector rotary is pressed two times, it is acceded again to the
screen of Power and C/N ratio measurement (section 4.2.3.1.4).
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USER'S MANUAL. PROMAX-10
, the PROMAX-10 carries out a
04/2004