The output of the VCO is amplified to a level of about 0 dBm by Q401 and Q402. Q603 with
R602, R603, CR601, C603 and C604 act as a very low noise power supply filter for the VCO.
8.1.2
TRANSMITTER
PA Driver Stages
The output of the VCO buffer drives Q204 and Q203 to provide a drive level to the RF PA device
of about +17 dBm. The supply voltage to this stage is switched on in transmit by Q202 and
Q201.
PA Module, Lowpass Filter, and T/R Switch
When driven by +17 dBm, the PA module, U201, is capable of producing full rated power at the
antenna connector. Pin 2 of the module is used for power control. The output power level can be
varied from 5 watts to full power by changing the voltage at this pin.
To reduce carrier frequency harmonics of the PA module output to acceptable levels, lowpass
filters are inserted between the module and the antenna connector. To isolate the PA module
from the receiver, an electronic T/R switch is used. The switch is formed around PIN diodes
CR201 and CR202 which are turned on in transmit and are off in receive.
