User's Manual

8.2.2 Transmitter
PA Driver Stages
The output of the VCO buffer drives 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 Q201 and Q202.
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 less
than 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 CR101 and CR201 which are
turned on in transmit and are off in receive.