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 9
the channels Reserve Gain attenuation. The next
stage is a distribution amplifier which is used to
overcome splitter losses in the base control unit.
Following the amplifier is a variable attenuator that
allows adjustment of the Distribution attenuation.
Signals are then applied to a 16-Way splitter for
distribution to the station receivers.
CMU
The CMU style base control unit is designed to
interface the TTA to the GTR8000 radio system
and does not include the receiver multicoupler
function. There are no individual receiver ports or
expansion ports provided since the receive distri-
bution function is performed in the GTR8000. The
specifications for the CMU are listed in
Table 4 . A
top view and a back view of the deck are shown in
Figures 6 and 7 respectively.
FUNCTIONAL BLOCK DIAGRAM
The functional block diagram of the system is
shown in
Figure 8 . RF signals enter the tower top
box and are passed thru a multi-resonator prese-
lector tuned to pass 792 to 824 MHz. After filtering
the signals are amplified by the active tower top
LNA (either amp A or B depending on user selec-
tion) before passing through the main transmission
line to the ground based control unit. The input of
each tower top LNA has a test signal port which
allows test signals from the base control units front
panel test port to be coupled into the systems RF
signal path. There is a 33.5 dB loss associated with
test signals injected into the system. The user has
the ability via software interface to switch the tower
top LNA’s input, between either the antenna or an
internal 50 Ohm load. This feature gives field engi-
neers the ability to perform system sensitivity tests
from the ground with or without site noise being
coupled into the system via the antenna.
RF signals from the tower top box are applied at
the rear of the CMU style base control unit at the
TRANS input connector. After passing onto the
deck they are applied to a modem assembly which
is used to couple and de-couple the 2.176 MHz
modem subcarrier communications between the
MCU
CMU
Tower Top Box
Main
Trans
Test
Port
Antenna
Test
Port
Test
Main
Transmission
Main
Transmission
Station
Receivers
Main
Trans
Test
Port
Figure 9: Cable connections for system components.