Frequency Generation Unit (Fgu) - Hytera DMR Service Manual

Service Manual
out-of-band spurious signals, and then feed to the two-stage IF amplifier circuit (composed of Q6133 and
Q6134) for amplification. Finally the amplified signals go to the IF IC for processing
13.2.2 Receiver Back-end
Figure 13-3 Diagram of IF Processor
The first IF signal (73.35MHz) output by the IF amplifier goes into IF IC via Pin 47, where the signal is
converted to the second IF signal (2.25MHz). Then the un-demodulated digital I/Q signal output from the
SSI interface is sent to U302 for demodulation. IF IC employs a reference frequency of 19.2MHz and
shares the crystal with U302. The second LO VCO consists of the external transistor, varactor and some
other components, to provide the second LO signal. The 18MHz clock frequency is generated by the LC
resonance loop (D702, L715 and C745).
DSP (U302) gets the audio signal from IF IC (U701). Then this signal goes through U302 to output data
signal, which is sent to U231 and PIN44 (SSI_DI) for digital-to-analog conversion. Finally, the output
analog audio signal will be subjected to gain control, and then fed to the speaker.

13.3 Frequency Generation Unit (FGU)

13.3.1 PLL Synthesizer
The PLL synthesizer that consists of the reference oscillator (X100), PLL IC (U100) and VCO, is utilized
to supply excitation signal source to the transmitter, and local oscillator signal to the receiver.
13.3.2 Reference Oscillator
X100 is a 19.2MHz TCXO, and its reference frequency is calibrated by the digital-to-analog converter
(U500) for accuracy.
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