DP770 Service Manual
T
he first IF signal (73.35MHz) output by the IF amplifier goes into AD9864 (UHF: U201, VHF: U91) via Pin
47 and completes the second mixer, where the signal is converted to the second IF signal (2.25 MHz). The
second IF signal is converted to digital signal via ADC sampling, and output via the SSI interface. Finally,
the digital signal is sent to DSP (OMAP138) for demodulation.
AD9864 employs reference frequency of 12.8MHz. The second local oscillator is composed of an external
oscillator, a varactor and some other components, to provide the (UHF: 71.1MHZ, VHF: 49.4MHz)
71.1MHz LO signal. The 18MHz clock input frequency of AD9864 is generated by the LC resonance loop.
3.1.3. Frequency Generation Unit
Figure 3-5 Frequency Generation Circuit Diagram
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