MINI-LINKEandEMicro
3.5.2.5 Transmitter Block
Transmitter O scillator (MCM)
The frequency of the transmitter is controlled in a Phase Locked Loop (PLL) (a
sample of the VCO signal is fed to a divider and fur ther on to a programmable
phase detector). An unlocked VCO loop generates a transmitter frequency
alar m.
Multiplier (MCM)
The VCO signal is amplified and frequency multiplied (2 or 4 times depending
on channel frequency).
Power Amplifier (MCM)
The transmitter output power is controlled by adjustment of the gain in the final
amplifier. The output power is set in steps of 1 dB through the operation and
maintenance system. The transmitter can be switched on or off by switching
the final amplifier.
3.5.2.6 Output Level Control
The output signal level from the final amplifiers are analyzed in order to see if
transmitted power is within specified range (output power alarm).
3.5.2.7 Receiver Block
The received signal is fed from the input branching filter into a low noise
amplifier and a down-converter to the first IF of 974 MHz (Receiver MCM).
After bandpass filtering and amplification, the signal is down-conver ted to the
second IF of 140 MHz (IF Converter). A portion of this 140 MHz is used in the
RSSI. The 140 M Hz signal from IF Converter is amplified and fed to t he cable
interface. This double down-conversion with a high first IF enables frequency
selection over a wide frequency band, with excellent receiver spurious and
image rejection.
Receiver Oscillator and Multiplier (MCM)
The local oscillator signal used in the first down-conversion is generated in the
same way as for the transmitter oscillator. The signal is multiplied (2 or 4 tim es
depending on channel frequency) and amplified.
3.5.2.8 IF Oscillator
The oscillator consists of a Phase Locked Loop (PLL) and a VCO. It is used for
the second down-conversion to 140 MHz. The VCO is also used for adjustment
38
AE/LZT 110 2012 R8C 2002-03-04
To Next Page
Loading...