Motorola Cleartone CM5000 Basic Service Manual page 31

OVERVIEW
Received signal from antenna switch is fed to the double tuned band pass filter and unwanted signal
is rejected at the filter. This filter is voltage controlled tunable filter.
The control voltage is fed to the filter via the buffer amplifier (IC471).
Output signal from the filter is amplified by the RF amplifier (TR401) and fed to the attenuator circuit
(IC402 ad IC403). This attenuator is used to expand the dynamic range of the receiver and it is
switched according to received signal strength. Attenuator control signal is fed to the attenuator via
the transistor (TR470) and IC (IC472).
Output signal from the attenuator is filtered by the 2nd double tune band pass filter and fed to the 1st
mixer (TR402). This band pass filter is also tuned by the control voltage.
The 1st mixer is N-channel dual gate MOS FET. The received signal is fed to the Gate 1 and the
local signal is fed to the Gate 2 of the FET.
The received signal is converted to the 1st IF signal. The converted 1st IF signal is 73.9 MHz and it
is fed to the 1st IF circuit.
Figure 3.
Receive
signal
BPF control signal
First IF stage
The 1st IF stage consists of the crystal filter (FL470). The output signal from the 1st mixer id fed to
the input of the crystal filter (FL470), and unwanted signal is filtered. The output signal of the filter is
fed to the 2nd IF stage.
Second IF stage
The second IF stage consists of IF IC (IC470) and Ceramic filter (FL471). The IF IC consists of 2nd
Mixer and AGC amplifier.
The IF IC is consists of the 2nd Mixer and AGC amplifier.
CM5000 Mobile Repeater/Gateway - Basic Service Manual
Receiver RF amplifier and Mixer Block Diagram
BPF BPF
Buffer
Amp
Figure 4.
1st
Mixer
Receive RF
amplifier
and Mixer
BPF BPF
1st Local input
1st IF Stage Block Diagram
1st X' tal
Filter
1st IF stage 2nd IF stage
BPF 2nd Mixer
2nd
Mixer
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