Motorola Cleartone CM5000 Basic Service Manual page 32

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Received signal from the 1st IF filter and 2nd local signal from the PLL are fed to the input terminal
of the 2nd mixer in the IF IC. Then 1st IF signal is converted to the 450 kHz 2nd IF signal. The signal
from the 2nd Mixer is connected to the AGC amplifier in the IF IC through 450 kHz ceramic filter.
Amplified signal at the AGC amplifier is fed to the ADC in the control circuit.
The AGC amplifier is controlled by the AGC voltage to maintain constant output voltage so as to
maintain appropriate ADC input voltage.
Control circuit determines the gain of AGC amplifier, and it generates the DC voltage by DAC and
fed to the AGC amplifier via the buffer amplifier (IC471).
From 1st
PLL (Phase lock loop) frequency synthesizer
PLL (Phase lock loop) frequency synthesizer consists of two main blocks. One is RX 1st Local PLL
frequency synthesizer block and the other one is 2nd Local PLL frequency synthesizer.
1st Local PLL
The 1st Local PLL is consists of the PLL IC (IC501), Loop filter, VCO (HC501) and peripheral circuit.
To realise the TETRA TDMA burst signaling at high speed, fractional N counter type synthesizer is
used.
The 1st local signal is fed to the 1st mixer (TR402) in the receiver circuit and transmit mixer
(CD1002).
2nd Local PLL
The 2nd local PLL consists of the PLL IC (IC1001), Loop filter, VCO (TR1001), buffer transistor
(TR1003 and TR1004) and peripheral circuit.
Output signal of the VCO (TR1001) is amplified by the amplifier (TR1003 and TR1004). This signal
is divided into 2, one is feed back to the PLL IC. The other signal is fed to the receive mixer and the
transmit mixer through the buffer amplifier (TR1004).
This PLL generates constant frequency in RX and TX.
Output signal of the 2nd PLL is fed to the 2nd mixer in the IF IC (IC470) and transmit mixer
(CD1002).
CM5000 Mobile Repeater/Gateway - Basic Service Manual
Figure 5. 2nd IF stage and AGC amplifier Block Diagram
2nd
IF
Mix
2nd Local
Signal
Ceramic
Filter
AGC
Amp
1st IF stage
AGC control
signal
OVERVIEW
ADC