User's Manual

SECTION 1: THEORY OF OPERATION
M32450-25-FCCRpt.doc Page 8
Transmitter/TR Switch
The transmitter section consists of an amplifier (U3) and an op amp (U4). To transmit, 5-volt power is
applied to the KEYPWR line. PA12V line is also powered up. This causes power amplifier (U2) to boost
the RF power to the desired level. Up to 40 watts are available from the transmitter. Harmonic
suppression is provided by C13, L2, and L3.
Power and Analog Ground
These sections consist of the power supplies and transmit control circuitry. Power from the vehicle’s
battery appears at VBATT. Diode D1 protects the voltage regulators by clamping any transient spikes on
the supply line. Such spikes typically occur while the engine is started. The supply line powers a series
of voltage regulators and the transmitter control circuitry, as follows:
 Voltage regulator VR1 provides 8-volt power for most other sections in the radio.
 Voltage regulator VR2 powers the transmit driver and T/R switch diodes as controlled by the
microcontroller.
 Voltage regulator VR3 provides a low noise 3.3-volt source for the radio electronics.