BIRD 424-86A-03, Инструкция по установке и эксплуатации

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TX RX Systems Inc. Manual 7-9322-5 08/09/06 Page 16
• Record the sensitivity with antenna on the data
sheet and MCA front panel (effective sensitiv-
ity).
This allows us to determine the effective system
sensitivity in the presence of site noise. In general,
the sensitivity measured with the antenna will be
less than that measured with the dummy load
unless site noise is at a minimum. Measured val-
ues of -89 dBm ± 2 dB are typical.
Spectrum Analysis
If the sensitivity measurements yield acceptable
results then the last test that needs to be done to
the system is to observe the signal levels at the
output ports of the MCA. The object of this test is to
verify that no signals exceed a certain maximum
power level. Excessively strong signals may cause
carrier desense of the receivers or contribute to
Intermodulation type interference.
Figure 12 shows the equipment interconnection for
this measurement while Figure 13 is a graph which
indicates the maximum desired measured-signal
levels both inside and outside of the transmit and
receive bands. TTA filter selectivity and antenna
space isolation are the dominant factors that deter-
mine the signal levels observed. Excessively
strong receive signals indicate the need for addi-
tional attenuation in the MCA. Transmit signals that
exceed -55 dBm indicate the need for additional fil-
tering ahead of the MCA or an increase in antenna
isolation. Antenna isolation is a function of the
spacing between the transmit and receive anten-
nas and may have to be lived with.
Antenna Sweep Test (Mode 2)
Place the system into Test Port Mode 2. During
this test the front panel test port is connected
directly to the antenna through the antenna port on
the tower top box. The equipment is connected as
shown in
Figure 14 . Using a Site analyzer, such as
the Bird Electronics Model SA-6000EX, mainte-
Test
Port
Bird ® Electronic
Model SA-6000EX
Site Analyzer
®
MCA
Daughter
Board
Input
Diagnostic
Cable
Antenna
Sampler
Port Output
Preselector
Input
Switch
Output
Switch
Main Test Ant
Figure 14 : Antenna Sweep Test.