Figure 3-9. Transmitter (700/800 Mhz) Block Diagram - Motorola APX 3000 Basic Service Manual

3-6
TX Buffer Amp
TX Driver Amplifier
TX VCO
TX/RX
VCO
RF Switch Matrix
3.2.2.1 UHF1/UHF2 Transmit
Once a UHF frequency for transmit has been selected, the Trident IC and the accompanying logic
circuitry will enable the voltage controlled oscillator which then generates the desired transmit
frequency. This transmit signal is then routed to the TX buffer amplifier which amplifies the signal.
The signal is routed to the UHF1/UHF2 Driver amplifier and then to the discrete final power amplifier.
The signal now goes through the antenna switch which routes the power to the harmonic filter which
will filter out the harmonics of the carrier signal and then passes through a directional coupler. The
Log Amp power detector monitors the output of the directional coupler and adjusts the control
voltages to the driver amplifier and final power amplifier. Finally, the RF signal is routed to the main
antenna.
3.2.2.2 VHF Transmit
Once a VHF frequency for transmit has been selected, the Trident IC and the accompanying logic
circuitry will enable the voltage controlled oscillator which then generates the desired transmit
frequency. This transmit signal is then routed to the TX buffer amplifier which amplifies the signal.
The signal is routed to the VHF Driver amplifier and then to the discrete final power amplifier. The
signal now goes through the antenna switch which routes the power to the harmonic filter which will
filter out the harmonics of the carrier signal and then passes through a directional coupler. The Log
Amp power detector monitors the output of the directional coupler and adjusts the control voltages to
the driver amplifier and final power amplifier. Finally, the RF signal is routed to the main antenna.
3.2.2.3 700/800 MHz Transmit
Once a 700/800 MHz frequency for transmit has been selected, the Trident IC and accompanying
logic circuitry enable the correct voltage controlled oscillator which then generates the desired
transmit frequency. This transmit signal is then routed to the TX buffer amplifier which amplifies the
signal. The signal is routed to the 7800 Driver amplifier and then to the discrete final power amplifier.
The signal now goes through the antenna switch which routes the power to the harmonic filter which
will filter out the harmonics of the carrier signal and then passes through a directional coupler. The
Log Amp power detector monitors the output of the directional coupler and adjusts the control
voltages to the driver amplifier and the discrete final power amplifier. Finally, the RF signal is routed
to the main antenna.
Antenna
Switch
Transmitter Final
FET 7/800 Mhz
Loop Filter

Figure 3-9. Transmitter (700/800 MHz) Block Diagram

Basic Theory of Operation: Analog Mode of Operation
Directional
Harmonic
Coupler
LP Filter
TO RX
Trident IC Ref. Oscillator
Synthesizer
Log Amp Power Detector
Digital RF Attenuator
Antenna Connector
Reverse Power
Detection
GPS