Tektronix MTM400 Manuel d'utilisateur télécharger pdf (Page 169)

Interface Configuration and Interpretation

MTM400 MPEG Transport Stream Monitor User Manual 3-125

The following graphs are available when the COFDM interface card is installed:

RF constellation (all data carriers)

When the receiver is in RF lock, the constellation points are

displayed. Note that according to ETR290, only the data pilots

are used for MER and EVM calculation. The samples collected

are not real time, so there is some dwell (delay) before a

complete constellation is displayed. The persistence of the

display can be varied using the Persist slider control at the

bottom of the graph.

MER and EVM calculations are performed on the constellation

data according to the formulae given in ETR290-101. Note that

this calculation specifically excludes the TPS carriers.

Overall SNR (all continuous pilots)

A time-line graph of measured Signal-to-Noise Ratio is

displayed, over a period of the preceding 255 seconds.

Overall MER (all data carriers)

A time-line graph of measured Modulation Error Ratio is

displayed, over the preceding 255 seconds.

Linear Amplitude response (selected carriers)

A linear amplitude response is shown for the carriers selected

using the carrier START and STOP controls. Allows you to

view and zoom in on frequency-dependent amplitude

distortions.

Impulse response

A channel response graph is shown, allowing time-related

distortions, particularly echoes, to be displayed relative to the

main signal. Echoes occurring before and after the main signal

are displayed. It is derived form the linear amplitude response,

transformed into the time domain.

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Tektronix MTM400 Manuel d'utilisateur Page 169