54
You can select the channel using
Frequency, MHz:,
Channel:
or
Channel Name:
fields. Modulation parameters fields will automatically take the values defined in the
channel plan for this channel. The measurement mode will turn on in a few seconds after
the new parameters have been set.
In
Synchronization:
field you can see demodulator status:
a) Channel locked:
b) Channel low level:
c) Demodulator trying to lock channel:
The
MER, dB,
preBER
and
postBER
parameters describe the input signal quality.
MER, dB
data field displays the measured modulation error ratio. The indicator to the right
from the data field gives the graphic representation of the measured value.
Noise margin,
dB
shows the margin (in dB) of
MER
parameter to
postBER
threshold value (2x10
-4
).
The
preBER
data field displays the bit error rate before Viterbi decoder. The preBER
value is also represented on the graphic indicator. The
postBER
data field displays the bit
error rate after Viterbi decoder. The postBER value is also represented on the graphic
indicator.
The
Tune error, MHz
data field displays the frequency tuning error between the defined
and the real values. The tuning error is also represented on the graphic indicator.
The
Error counter
data field displays the number of errors detected during the time
indicated in the
Accum. period
field.
Reset
button allows to zero the error counter and
restart the counting process.
In the right part of the screen you can see the constellation diagram of the signal with
quadrature-amplitude modulation COFDM, which is the graphic representation of vector
diagram. The diagram is divided into four quadrants, each containing dots made by the
peaks of the vectors of demodulated signals quadratures. In the ideal case the diagram
represents a number of dots (nods) on the phase plane. For example for QAM64 it will be
64 dots for data subcarriers and 4 dots for pilots subcarriers. The noise influence makes
the dots to ‘spread’ into spots. Analysis of the form of the dots and their distribution on the
phase plane makes it possible to define the noise behavior. The color of the diagram parts
depends on how often the dots fall within these parts. The parts with the lower number of
dots are blue. The parts with the highest number of dots are red.
4.10.10. Data Logs Management
4.10.10.1. General Information
The IT-088 TV Signal Analyzer allows saving the measured results into the specially
organized memory. The channel data logs store the measurement results as channel
parameters. The view of a channel data log page is shown in figure 4.44.
Summary of Contents for IT-088
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