User's Manual

P.G. TM0054RB
2-1
SECTION 2. THEORY OF OPERATION
2.1 THEORY OF OPERATION
The R280 is a bidirectional repeater, providing gain in both the uplink and downlink
frequency bands. The block diagram of the R280 is shown in Figure 2-1. The PCS
unit has a typical gain of 70 dB in both the uplink and downlink bands. The cellular
and SMR units have typical gains of 75 dB in both the uplink and downlink bands. The
unit is composed of IF conversion modules, amplifiers, and diplexers as well as a
control module.
Please refer to Figure 2-1. The downlink signal enters the unit via the Base Antenna
connector. After the signal passes through the high band port of the diplexer within the
Uplink Amp module, the signal is split and then fed into the 2 Downlink IF Conversion
Modules. The modules use IF conversion to provide sharp filtering of downlink signals
in order to reject out of band signals. The conversion modules have a typical gain of
50 dB. After the 2 downlink signals are combined within the Downlink Amp module,
they are fed into the downlink amp and then into the high band port of the diplexer
within the Downlink Amp module. The downlink signal then appears at the Distribution
Antenna connector.
The unit's operation in the uplink band is similar to the downlink band discussed in the
previous paragraph but uses the Uplink IF Conversion Modules along with the uplink
amp in the Uplink Amp module and the low band ports of the diplexers to provide gain
from the Distribution Antenna to the Base Antenna.
The Controller module sets the center frequency of the IF conversion modules. When
the unit is first switched on, the controller module sends a signal to set the center
frequency of the IF conversion modules. It then enables the modules once the PLLs
have locked and stabilized to the specific band of operation. The controller is pre-
programmed at the factory with the correct customer frequencies.
The controller module also contains the attenuation control. The rotary switch on the
module adjusts the attenuation setting of both the uplink and downlink IF conversion
modules to the value indicated by the switch knob pointer. The attenuators can be set
over the range of 0 to 30 dB in 2 dB steps. Changing the setting has a immediate
affect on the attenuators.