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403 – 447 MHz UHF1 Theory Of Operation:
UHF1 Transmitter
11-3
11.3 UHF1 Transmitter
The UHF1 transmitter covers the range of 403 – 447MHz. Depending on model, the output power of
the transmitter is switchable on a per-channel basis between high power (4 Watt) and low power (1
Watt). The transmitter is divided into four major blocks as shown in Figure 11-2.
• Power Amplifier
• Harmonic Filter
• Antenna Matching Network
• Power Control.
Figure 11-2. UHF1 Transmitter Block Diagram
11.3.1 Power Amplifier
The transmitter power amplifier has three stages of amplification – Pre Driver (Q401), Driver Amp
(Q402) and Final Amp (Q403). Signal from TX VCO is applied to the pre driver via an attenuator
circuit. The attenuator is pie style resistor attenuator, and is used as isolation between VCO and the
power amps. The -4dBm TX RF signal from attenuator is then amplified by pre driver and driver amp
to 25dBm and is applied to the final amp. The final amp (Q403) is an enhancement-mode
N-channel MOSFET device providing a gain of 12dB. The device drain current is drawn directly from
the DC battery supply voltage input via L413. A matching network consisting of C416, C417, C418,
C419, C420, C451, C422, C452 and a strip line, transforms the impedance to approximately 50Ohm.
11.3.2 Antenna Switch
An antenna switch works mainly as a switching device between transmit and receive paths. In
transmit mode (PTT), Q407 is turned on and both PIN diodes (CR401, CR301) are forward biased
into conduction. This enables the RF signal to pass to the harmonic filter and then to the antenna. In
the receiver mode, both diodes are off. Signals applied to the antenna jack are routed via the LPF
(harmonic filter), through network L409, L410, L411, C426, C427, C428, C429, C430, C445, C446 to
the receiver input.
11.3.3 Harmonic Filter
The harmonic filter consists of components L409, L410, L411, C426, C427, C428, C429, C430, C445
and C446. The harmonic filter is a seven-pole elliptic filter.
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Summary of Contents for P100 Series
Page 1: ...P100 Series Portable Radios Detailed Service Manual ...
Page 2: ......
Page 8: ...iv Notes ...
Page 18: ...xiv List of Tables Notes ...
Page 22: ...xviii Summary of Printed Circuit Boards and Bands Available Notes ...
Page 30: ...Notes 2 4 Test Equipment Service Aids and Service Tools Service Aids ...
Page 54: ...7 4 UHF2 Schematic Diagrams Overlays and Parts Lists Speaker and Microphone Schematic Notes ...
Page 128: ...7 78 Circuit Board Schematic Diagram and Parts List UHF2 435 480 MHz Notes ...
Page 150: ...7 100 Circuit Board Schematic Diagram and Parts List UHF2 MDC QCII R TTE 435 470 MHz Notes ...
Page 166: ...10 4 VHF Schematic Diagrams Overlays and Parts Lists Speaker and Microphone Schematic Notes ...
Page 192: ...10 26 Circuit Board Schematic Diagram and Parts List VHF 136 174 MHz Notes ...
Page 218: ...10 52 Circuit Board Schematic Diagram and Parts List VHF 136 174 MHz Notes ...
Page 242: ...10 76 Circuit Board Schematic Diagram and Parts List VHF MDC QCII R TTE 136 174 MHz Notes ...
Page 258: ...13 4 UHF1 Schematic Diagrams Overlays and Parts Lists Speaker and Microphone Schematic Notes ...
Page 328: ...13 74 Circuit Board Schematic Diagram and Parts List UHF1 MDC QCII R TTE 403 447 MHz Notes ...
Page 332: ...A 4 Warranty Service Support and Replacement Parts Further Assistance From Motorola Notes ...
Page 335: ......