9-8 MTR3000 Radio Frequency Distribution System (RFDS) Equipment: Functional Theory of Operation
9.3 Functional Theory of Operation
9.3.1 Base Station/Repeater Preselectors
The Preselector rejects unwanted signals including the transmitter signals from overloading the
Receiver. The filter is usually not required when using a Receiver multicoupler system. This filter can
be retuned in the field.
9.3.2 Antenna Relay
The Antenna Relay Module contains a relay with a set of normally open and normally closed
contacts. The relay coil is controlled by the Antenna Relay signal from the Station Control Module to
connect either the Receiver Module or the PA to a single transmit/receive antenna.
9.3.3 External Dual Circulator Tray
The double circulator assembly accepts transmit RF output power from the PA and provides 45 dB of
isolation between the PA and the transmit antenna. The assembly consists of two circulators in a
single case, each with a 50 Ω load. Each circulator allows forward RF energy to pass through to the
output, while routing any reflected RF energy to the corresponding 50 Ω load.
Most of the reflected energy is absorbed by the 50 Ω load (heat sink) mounted connected to the
second circulator. A thermistor mounted on the heat sink provides a variable resistance signal
proportional to the heat sink temperature. This signal is routed to the Station Control Module via the
Temp Sense cable and the backplane interface board. If the heat sink temperature exceeds a preset
threshold, the base station/repeater software enables PA rollback mode to a reduced output power.
Terminations Female N-Type
Input and Output Impedance 50 Ω
Note Refer to "Appendix A" for the model number.
Set the “Antenna Relay Delay Timer” minimally to 50 ms in the
Customer Programming Software (CPS) to ensure that the Antenna
Relay is physically in proper position during transmitter key-up.
Damage to the antenna relay will result if a value less than 50 ms is
entered into the CPS.
Note
With the relay de-energized, the antenna is connected to the Receiver Module. To connect
the antenna to the PA, the Station Control Module must energize the relay (one side of
which is connected to +14.2 VDC) by grounding the Antenna Relay signal.
Note
The functionality of RF Peripherals port (temperature monitoring) is not supported.
Table 9-7 MTR3000 Antenna Relay Specifications (Continued)
Antenna Relay Spec Limit
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