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Theory of Operation
: VHF Transmitter
2-19
2.12 VHF Transmitter
The VHF transmitter consists of the following basic circuits as shown in
• Power amplifier
• Antenna switch/harmonic filter
• Antenna matching network
• Power control integrated circuit (PCIC)
2.12.1 Power Amplifier
The power amplifier consists of two devices:
• 9Z67 LDMOS driver IC (U3501)
• PRF1507 LDMOS PA (Q3501)
The 9Z67 LDMOS driver IC contains a 2 stage amplification with a supply voltage of 7.3V.
This RF power amplifier is capable of supplying an output power of 0.3W (pin 6 and 7) with an input
signal of 2mW (3dBm) (pin16). The current drain would typically be 130mA while operating in the
frequency range of 136–174MHz.
The PRF1507 LDMOS PA is capable of supplying an output power of 7W with an input signal of
0.3W. The current drain would typically be 1800mA while operating in the frequency range of
136–174MHz. The power output can be varied by changing the biasing voltage.
2.12.2 Antenna Switch
The antenna switch circuit consists of two PIN diodes (D3521 and D3551), a pi network (C3531,
L3551 and C3550), and two current limiting resistors (R3571, R3572, R3573 ). In the transmit mode,
B+ at PCIC (U3502) pin 23 will go low and turn on Q3561 where a B+ bias is applied to the antenna
switch circuit to bias the diodes "on". The shunt diode (D3551) shorts out the receiver port, and the
pi network, which operates as a quarter wave transmission line, transforms the low impedance of the
shunt diode to a high impedance at the input of the harmonic filter. In the receive mode, the diodes
are both off, and hence, there exists a low attenuation path between the antenna and receiver ports.
Figure 2-13. Transmitter Block Diagram
PCIC
Antenna
P A
Driver
Vcontrol
Vcontrol
From VCO
Jack
PA-Final
Stage
Antenna Switch/
Harmonic Filter/
Matching Network
Summary of Contents for PR860
Page 1: ...PR860 Two Way Portable Radio Detailed Service Manual ...
Page 2: ......
Page 5: ...iv Notes ...
Page 9: ...viii Table of Contents Notes ...
Page 13: ...Notes xii List of Figures ...
Page 17: ...1 4 Introduction Radio Model Information Notes ...
Page 51: ...2 34 Theory of Operation Voltage Control Oscillators VCO Notes ...
Page 81: ...4 4 Schematic Diagrams Overlays and Parts Lists Flex Layout Notes ...
Page 193: ...4 116 Schematic Diagrams Overlays and Parts Lists Low Band Section Notes ...
Page 196: ......