Interface Configuration and Interpretation

Receiver Mode: In order to achieve high accuracy measurements, particularly for MER and SNR measurements, the COFDM IF card supports two modes of operation.

 

For conventional COFDM reception, a relatively low ultimate

 

SNR is acceptable. For example at 64QAM, an ultimate receiver

 

SNR of 30 dB can result in a reduction in system performance of

 

only 0.5 dB. However, for more detailed analysis of COFDM

 

constellations, a much higher ultimate SNR is required,

 

preferably in excess of 40 dB. For this reason, two modes of

 

COFDM operation are provided.

 

High Sensitivity mode gives the full dynamic range of a

 

conventional COFDM receiver, but at the expense of ultimate

 

SNR. The High Resolution mode modifies the signal path to

 

dramatically reduce the noise generated in the receiver, giving a

 

much higher ultimate SNR, but at the expense of receiver

 

sensitivity. So for general purpose monitoring where the input

 

signal may vary over a wide range, typically -75 dBm and

 

lower, high sensitivity mode is preferred.

 

If the signal is consistently greater than -50 dB, high resolution

 

mode provides better RF measurement performance.

IF Filter

The COFDM receiver incorporates two stages of selectivity.

 

One of these can be bypassed in WIDE mode to give a more

 

accurate representation of the input spectrum flatness (at the

 

expense of overall selectivity).

Stream Priority When hierarchical modulation is present, the transport stream priority, HIGH or LOW, can be selected for analysis by the MPEG analyzer tools. When no hierarchy is present, this defaults to HIGH priority.

Carrier start When observing carrier amplitudes ahead of the channel equalizer, this value sets the numerical value of the first carrier to be displayed., and defaults to zero.

Carrier end When observing carrier amplitudes ahead of the channel equalizer, this value sets the numerical value of the last carrier to be displayed, and defaults to the maximum carrier number in the COFDM signal (1704 for 2K, 6816 for 8K modes).

Front End Lock If full lock is acquired onto the channel and it is receiving the signal correctly, the Front End Lock (FEL) indicator will light up green. When a signal is present but no lock is achieved, the indicator is red. When no signal is found, the indicator is gray.

MTM400 MPEG Transport Stream Monitor User Manual

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