USER’S MANUAL. PROMAX-10
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Page 26
11/2008
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 21.-
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
Premium
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 (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
.
The
PROMAX-10
Premium
, 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 (
Post-BER
measurement (
BER
after
FEC)
shown as
BER
;
Pre-BER
measurement (
BER
before
FEC
) shown as
BER)
, the modulation error ratio
measurement (
MER
), the represented quadrants and the type of detected codification.
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