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Receiver Back-end
The processed first IF signal is sent to IC BA4116 for second mixing with the second harmonic signal
(selected as the second LO signal) of the PLL crystal to get the 450 kHz second IF signal. Then the first
IF signal passes through the 450 kHz ceramic filter which filters out the spurious signal before the
second IF signal is amplified and frequency-discriminated. After that, the filtered first IF signal is
processed internally and demodulated. Finally, the demodulated signal will be sent to the baseband
section for audio processing.
5.2.3 Frequency Generation Unit (FGU)
The FGU circuit is composed of VCO and PLL. It is the core module of the TX/RX system. This circuit
provides accurate carrier frequency when the radio is transmitting, and stable LO signal when the radio
is receiving. It plays an important role and determines the performance of the system.
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