Hytera HD785 - Page 5

Contents Service Manual
ii
7.1.1 RF Power Amplifier Circuit
..................................................................................................32
7.1.2 Low-pass Filter Circ
uit ........................................................................................................33
7.1.3 Auto Power Control Circuit
..................................................................................................33
7.2 Receiver Circuit
.............................................................................................................................33
7.2.1 Receiver Front-end
.............................................................................................................34
7.2.2 Receiver Back-end
.............................................................................................................35
7.3 Frequency Generation Unit (FGU) ................................................................................................35
7.3.1 Working Principle of PLL.....................................................................................................36
7.3.2 Working Principle of VCO
...................................................................................................37
7.3.3 Two-point Modulation
..........................................................................................................37
7.4 PCB Vie
w......................................................................................................................................38
7.5 Block Diagram
..............................................................................................................................46
7.6 Schematic Diagram
.......................................................................................................................49
7.7 Parts List.......................................................................................................................................65
7.8 Troubleshooting Flow Chart
........................................................................................................115
8. UHF2 (450-520MHz) Information
...................................................................................................121
8.1 Transmitter Circuit
.......................................................................................................................121
8.1.1 RF Power Amplifier Circuit
................................................................................................121
8.1.2 Low-pass Filter Circ
uit ......................................................................................................122
8.1.3 Auto Power Control Circuit................................................................................................122
8.2 Receiver Circuit
...........................................................................................................................122
8.2.1 Receiver Front-end
...........................................................................................................123
8.2.2 Receiver Back-end
...........................................................................................................124
8.3 Frequency Generation Unit (FGU)
..............................................................................................124
8.3.1 Working Principle of PLL...................................................................................................125
8.3.2 Working Principle of VCO
.................................................................................................125
8.3.3 Two-point Modulation........................................................................................................126
8.4 PCB Vie
w....................................................................................................................................127
8.5 Block Diagram
............................................................................................................................135
8.6 Schematic Diagram
.....................................................................................................................138
8.7 Parts Lis
t.....................................................................................................................................154
8.8 Troubleshooting Flow Chart
........................................................................................................205
9. UHF3 (350-400MHz) Information
...................................................................................................211
9.1 Transmitter Circuit.......................................................................................................................211
9.1.1 RF Power Amplifier Circuit
................................................................................................211
9.1.2 Low-pass Filter Circ
uit ......................................................................................................212
9.1.3 Auto Power Control Circuit
................................................................................................212
9.2 Receiver Circuit
...........................................................................................................................212