Interface Configuration and Interpretation

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).

MTM400 MPEG Transport Stream Monitor User Manual

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