Service Manual
266
ut-of-band interference signal generated during amplification, and to send wanted HF signal to
o
remove o
the mixer.
The wanted signal passes through the RF band-pass filter and low-noise amplifier and goes to the mixer
(U403). Meanwhile, the first local oscillator (LO) signal generated by VCO passes through the low-pass
filter and also goes to the mixer. In the mixer, the wanted signal and the first LO signal are mixed t
generate the first IF signal (44.85MHz). Then the signal passes through 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 goes to crystal filter (Z401) for filtering, and is sent to the two-stage IF amplifier circuit for
amplification. Then the amplified signal goes to the IF processor U501 for further processing.
Rear-end Circuit
16.8MHZ
Reference
frequency
IF input
SSI TO OMAP
Figure 12-3 Diagram of IF Processor
The first IF signal (44.85MHz) output by the IF amplifier goes into U501 via Pin 47, where the signal is
converted to the second IF signal (2.25MHz). Then the signal is converted to digital signal via ADC
sampling, and output via the SSI interface. Finally, the digital signal is sent to DSP (OMAP5912) for
demodulation.
U501 employs reference frequency of 19.2MHz and shares the crystal with OMAP. The second LO VCO
comprises an oscillator, a varactor and some other components, to provide the 42.6/47.1MHz LO signal.
The 18MHz clock frequency is generated by the LC resonance loop.
12.3 Frequency Generation Unit (FGU)
The repeater has two FGUs. One is RX FGU providing the first LO frequency for the RX system; the
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