Nortel DualMode 800, Maintenance Manual

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11-46 DRU tests
411-2051-500 Draft 00.01 November 1999
Bit error rate test at the cell site
The BER test performed at the cell site verifies the BER performance of the
DRU and the paths between the DRU and the communications monitor. It
does not verify the BER performance of the links between the DRU and the
DSPM.
In the inbound (RX) direction (from the communications monitor to the
TRU), the communications monitor generates a pseudo-random bit stream
(PRBS) onto the selected TDMA time slot of the TRU. This PRBS is looped
from the receiver of the TRU to the transmitter of the TRU and sent back to
the communications monitor. In the outbound (TX) direction, the
communications monitor expects to receive the same bit pattern. After a short
self-synchronization time period, the bit error rate is measured.
Service impacts
This BER test causes a reduction in the receive performance of the shelf
containing the TRU under test because of the loss of receive diversity.
The TRU transmit and receive tests must be performed before the BER test to
verify the TRU’s transmit and receive paths. This is because the TRU uses an
RF loopback to access the base-band receive signal. Failure to verify the
TRU transmit and receive paths may result in invalid test data.
Figure 11-10 shows the BER test setup at the cell site
Note: The sniffer port is at a level of -50 dBm lower than the level at the
antenna port of the duplexer. Make sure that this level meets the minimum
input level requirement of your communications monitor. If the level is
lower than the minimum requirement, connect the input of the
communications monitor to the antenna port of the duplexer. In this case,
the entire cell/sector will be out of service for the duration of the test.
CAUTION
Service interruption
The service of the shelf housing the TRU under test will be
affected. Perform the tests during low traffic period.
WARNING
RF radiation hazard
Do NOT disconnect any RF cables when transmitters are on.