TR850 Service Manual
POWERCONTROL control signal form the baseband will be sent to the identical phase input port of
IC100(NJM2904)’s operational amplifier. After the operational amplification and external circuit’s function
calculation, the signal is output as a conrol signal which controls the U100 gain control port to ensure that
the actual output power remains stable when the impedance matches and to decrease the output power
for power amplifier protection when the impedance mismatches.
Temperature Detection Circuit
The continuous temperature rise can lead to a decrease of transmitting power. The temperature detection
employs IC101(DS18B20) to collect the digital temperature sample.When the temperature exceeds the
threshold value, the fan will be switched on for heat dissipation.
3.1.3. Rx Module Circuit
Figure 3-3 Receiver Module
Receiver Circuit
The receiver circuit includes RF Band pass filter, Low-noise amplifier, mixer, IF filter, IF amplifier and IF
processor.
The signal from the receiving port first passes the low pass filter to suppress the high frequency
interference, and passes the electrical tuning BPF to suppress the image interference and the out-band
interference.The in-band signal is sent to the low noise amplifier (IC3000) and the amplified signal passes
the electrical tuning BPF controlled by BPFADJUST to filter the out-band interference, so the effective high
frequency will be sent to the mixer(IC3005). Meanwhile, the first local oscillation passes the LPF and gets
mixed with the effective signal in IC3005 to generate the first IF signal (51.65MHz). The first IF signal
passes the crystal filter (Z3001) to suppress the out-band signal. The signal is then sent to IF amplifier
(IC6003) for amplification before being sent to the crystal filter to strenghthen the suppression of the the
adjacent channel. After being sent to the limiting amplifier composed of Q3001 and Q3002, the signal
enters AD9864 (U4000) for the second frequency mixing ,IF amplification and AD sampling. The digital IQ
signal will be finally output to the baseband for further processing.
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