BIRD 428B-83H-01-C-110, Инструкция по установке и эксплуатации

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TX RX Systems Inc. Manual 7-9487-3 05/05/11 Page 25
Figure 25 and 26 shows the equipment intercon-
nection for this measurement while Figure 27 is a
graph which indicates the maximum desired mea-
sured-signal levels both inside and outside of the
transmit and receive bands. TTA filter selectivity
and antenna space isolation are the dominant fac-
tors that determine the signal levels observed.
Excessively strong receive signals indicate the
need for additional attenuation in the control unit.
There are three areas of the spectrum that must be
evaluated:
1) Receive Band - The spectrum where the
receive frequencies reside must not have carri-
ers above -35 dBm. These are the carriers that
are intended to enter the receiver. If subscribers
or control stations are near the infrastructure
the levels can be very high. If the levels are
above -35 dBM, the gain of the system must be
reduced or the source of the high level carrier
must be reduced.
2) Transmit Band - The highest carrier that the
receive system will consistently see is its own
transmitter. The preselector of the receive sys-
tem must adequately remove these carriers to
prevent over-drive. The goal of the preselector
is to reduce all transmit carriers below -55 dBm.
If the level of a transmitter is above -55 dBm the
preselector is not adequately performing its job
and must be changed.
3) All Other Frequencies - The receiver is
designed to monitor very low signals and there
must be a minimum amount of undesired
energy exposure. The preselector has very
sharp selectivity and must reduce all carriers
outside the bandwidth below -75 dBm except as
indicated above.
Procedure for Spectral Analysis
Spectral analysis will verify the signals arriving at
the receiver as well as validate the reserve gain
adjustment. To perform a spectral analysis of the
site follow the steps listed below.
1) Make sure programmable attenuators are prop-
erly adjusted.
Test Ant Main
Test Trans
Tower Top Box MCU
Spectrum Analyzer
Bird SignalHawk
Front Panel
Test Port
Antenna
Figure 25: Testing the output spectrum of the TTA. Model 428B-83H-01-M shown.