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Interface Configuration and Interpretation
MTM400 MPEG Transport Stream Monitor User Manual 3-115
Constellation Provides the option to set the modulation scheme: 4-QAM,
16-QAM, 64-QAM or 256-QAM.
Select the required value from the drop-down list.
Inversion The sense of modulation may be inverted due to the number of
mixing stages in the installation. Enabling the Inversion
checkbox will allow the demodulator to lock onto a received
signal with an inverted spectrum.
PLL Bandwidth
This control modifies the bandwidth of the carrier phase
recovery loop, which is responsible for de-rotating the incoming
symbols to establish a steady constellation. Two settings are
available: Normal and Wide. In Normal mode, the loop
bandwidth is approximately 3 kHz, which gives optimum
immunity to noise in the channel for most applications. In some
cases, the loop bandwidth may be too narrow to follow the
jittered signal, in which case the Wide bandwidth setting should
be selected. This increases the loop bandwidth to about 10 kHz,
which enables the MTM 400 to more easily acquire and track a
jittered constellation, but makes the demodulator more
susceptible to thermal noise. Normal is the default setting and is
recommended for most applications.
AFC Range Two carrier recovery ranges are available: Normal and Wide. In
Normal mode, the range is approximately ±150 kHz. In Wide
mode, the range is increased to ±500 kHz. Normal setting is the
default setting and is recommended for most applications.
Analysis Mode Two settings are available: MPEG mode and QAM mode. In
MPEG mode, the lock condition is declared as “No Lock” if a
valid transport stream cannot be detected. This prevents spurious
streams from being fed to the MPEG processor for analysis. In
QAM mode, the validity of the MPEG stream is ignored,
possibly resulting in spurious MPEG analysis, but allowing lock
to be asserted if the QAM receiver front end sees a valid QAM
signal. This allows the display of RF data and constellations
even if the MPEG data is not valid. In QAM mode, the
MTM400 behaves more like a conventional QAM analyzer.
MPEG mode is the default setting and is recommended for most
applications. The range controls, PLL bandwidth and AFC
range, are operable in both MPEG and QAM analysis modes.
BER Bit Error Rate (pre Reed Solomon).