Hytera HD705 - Receiver Front-End; Figure 7-2 Diagram of Receiver Circuit

UHF1 (400-470MHz) Information Service Manual
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Figure 7-2 Diagram of Receiver Circuit
7.2.1 Receiver Front-end
The HF signal from the low-pass filter passes through the electrically tunable band-pass filter controlled
via APC/TV1 level, to remove out-of-band interference signal and to send wanted band-pass signal to
the low-noise amplifier (Q9001). The amplified signal goes to a band-pass filter controlled via APC/TV1
level, to remove out-of-band interference signal generated during amplification, and to send wanted HF
signal to the mixer.
The wanted signal passes through the RF band-pass filter and low-noise amplifier and goes to the mixer
(D9017). Meanwhile, the first local oscillator (LO) signal generated by VCO passes through the low-pass
filter and also goes to the mixer (D9017). In the mixer, the wanted signal and the first LO signal are
mixed to generate the first IF signal (73.35MHz). Then the signal passes through a π-type attenuator
(2dB) and the LC, to suppress carrier other than the first IF signal, and to increase the isolation between
the mixer and the IF filter. After that, the first IF signal is processed by the crystal filter (Z9001), and is
sent to the two-stage IF amplifier circuit (composed of 2SC3356) for amplification. Then the amplified
signal goes to the IF processor AD9864 (U401) for processing.