Description
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2.4.2
Repeater chain
2.4.2.1
Overview
The function of the repeater chain is to transmit signals sent by the transmission terminal to
other terminals under the coverage of the IDR IDO 3G.
The repeater chain comprises a transmission and a reception chain. Certain
sub-assemblies are used for both transmission and reception mode.
2.4.2.2
Reception chain
The signals received by the antenna are routed by the duplexers to the LNA function.
Signal routing is carried out by a bandpass filter whose function is to select the reception
band and to eliminate unwanted frequencies.
The LNA function carries out a low noise amplification for the signals and sends them to
the 3G PA-TRX
module
(TRX function).
In the event of a failure of the LNA function (over or under power), the red “RX DEF” LED
on the duplexer lights aup and the "ALARM" connector's alarm loop opens.
The 3G PA-TRX
module
(TRX function) carries out the following processes on the signals:
• conversion to intermediate frequency (IF) in the RX receiver,
• demodulation and loopback on the transmission chain in the SP function.
2.4.2.3
Transmission chain
The reception signals looped backin the TS function of the 3G PA-TRX
module
(TRX function) are transmitted to the TX transmitter of the 3G PA-TRX
module
(TRX
function). The TX transmitter modulates the signals and transmits them to the 3G PA of the
PA-TRX
module
(PA function) at a level of + 12 dBm.
The PA module raises the level of the RF signals from + 12 dBm to an output level set at
+ 33.5 dBm, + 37.5 dBm, + 41.5 dBm or + 43.5 dBm depending on the gain command
supplied by the synchronisation board. This command depends on:
• the power level selected by the operator,
• any malfunction that may cause the transmission power to be reduced (temperature
alarm or 3G PA-TRX
module
alarm).
However, the 3G PA-TRX module can take self-protective action autonomously:
• change to reduced power (+ 31.8 dBm) if the SWR on output from the module is greater
than 3,
• module switches off if the temperature becomes too high.
