Service Manual UHF2 (450-520MHz) Information
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Pi Attenuator
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Figure 8-2 Diagram of Receiver Circuit
8.2.1 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.
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