Black Box Modem MD885A-R3 Manuel d'utilisateur télécharger pdf (Page 124)

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7.0 Diagnostics

7.7.5 E

XTERNAL

NALOG

OOPBACK

ELF

-T

EST

(ALXST)

The external analog loopback self-test is available for 4-wire leased line mode

only.

The ALXST places the modem in analog loopback and causes data to be sent

and received by an internal 511-bit pattern generator and receiver. No DTE

or external BERT is necessary. As shown in Figure 7-4, the test circuit includes

the leased lines (the external loopback).

NOTE

The ALXST may result in errors or may fail altogether even where

conditions are satisfactory for normal operation. The test channel

presented to the modem during the ALXST includes all impairments of

both the inbound and outbound channels (amplitude distortion, delay

distortion, noise, etc.). The main purpose of the ALXST is to verify that

the modem is connected to the leased-line and the leased line circuit is

complete. The test is not meant to assess the suitability of the leased

line.

Figure 7-4. External Analog Loopback Self Test (ALBST).

TRANSMITTER

PATTERN

GENERATOR

RECEIVER

PATTERN

DETECTOR

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Black Box Modem MD885A-R3 Manuel d'utilisateur Page 124