Transmit RF PA, T/R Switching, and Antenna LPF
Transmit/Receive Antenna Switch:
This part of the circuit is a set of on/off switches implemented
using MOSFET transistors. Q21 (FQN1N50C) has a 450 volt breakdown capability and is in OFF
mode during transmit. Q22 (2N7000) is ON during transmit and shunts RF to ground during that
period. Q26 (2N7000) is in OFF mode during transmit and blocks RF during transmit. Q24
(2N7000) is in ON mode during transmit and shunts RF to ground during that period. Q23 (2N7000)
is in OFF mode during transmit and blocks RF when transmitting. Together these switches pass
received signals around the RF PA section during receive and block high power RF feedback from
entering the RF PA input side during transmit.
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