Hytera MD78X, Service Manual

Page: 351 / 519

Circuit Description
UHF5 (806MHz
–
941MHz)
28
Voltag
e-
Controlled Oscillator (VCO)
BB IC
U302
PLL IC
U100
TX/RX_VCO
Q100
L P F
TX/RX_VCO
Q106
TX_VCO
Q103
TX_VCO
Q110
VCTCXO
X100
U105
SW
U102
SW
U101
TX LO
MOD H
CLK
STB
DATA
LD
Fast Lock SW
Fast Lock SW
U500
TX:935-941MHz;
Rx:851-870MHz
VCO_Fee
dback LPF
MOD L
4V3A
4V3A
4V3A
4V3A
5VA&3V3D
5V&3V3A
Attenuator
TX:896-902MHz;
TX:851-870MHz;
Rx:935-941MHz
TX:806-825MHz;
BPF1
806-941MHz
Q107
BPF2
806-941MHz
Q109
Switch
U6107
RX LO
VCO is composed of transistors (Q100, Q103, Q106 or Q110), varactors and Colpitts Oscillators. There
are four TX excitation signal sources: Q100, Q103, Q106 and Q110, of which Q100 and Q106 are also
used to receive LO signals. Q101, Q105, Q108 and Q112 control the operating frequency of the VCO.
U105 isolates the output of VCO circuit while Q107 and Q109 constitute a two-stage buffer amplifier.
The digital-to-analog converter IC (U500) modulates the TX oscillator signal.
5.4
GPS Circuit Section
GPS
module
U302
UART
GPS
Antenna
LCD
Power
REB-1315LPx
GPS data can be acquired via the programmable GPS key on the front panel of the mobile radio. The
GPS function is realized via REB-1315LPx module, which integrates GPS baseband processor circuits.
The GPS signal (1.57542 GHz), received via the GPS active antenna (with a built-in LNA), goes to the
GPS module for processing, and then enters U302 via the UART port. Meanwhile, U302 sends control
command to the GPS module and forwards processed GPS data to the LCD display.