Page 51 of 101
DWG ID: 181-0101-00A
Date: 2003-09-26
12.2.2.2
PA Module, Low-pass Filter, and T/R Switch
When driven by +17 dBm, the PA module is capable of producing 6 W or more of 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 0.5 W to full power by changing the voltage at
this pin.
To reduce carrier frequency harmonics of the PA module output to acceptable levels, a
low-pass filter is inserted between the module and the antenna connector. This filter is of
elliptic design and formed around a buried stripline transmission line and C164, C165,
and C166.
To isolate the PA module from the receiver, an electronic T/R switch is used. The switch
is formed around PIN diodes CR101 and CR104, which are turned on in transmit and are
off in receive. CR104 switches the PA module into and out of the circuit, while CR101
protects and isolates the receiver input when the radio is in transmit.
12.2.3
Miscellaneous Functions
Two on-board regulators are used to provide the 5 V dc used by most of the circuitry in
the radio. IC106 is a low noise, low dropout regulator which provides 5 V to all the
portions of the radio which do not get switched on or off as the radio changes from
transmit to receive. This regulator is enabled by the XCVR-EN (J102-5) input. When
this regulator is not enabled, the radio is essentially powered down. IC107 is an identical
regulator, which supplies voltage to those circuits which are to be powered-up only in
receive. The regulator is enabled through IC105E and F by the RX-EN (J102-4) input.
The transmitter PA module driver stages and the T/R switch are powered by +7.2 V
through Q113. Q113 is enabled by the TX-EN (J102-3) input, through delay and
sequencing circuitry formed around IC105, Q115, and Q114. The sequencing circuitry
delays PA turn-on until the driver stages and T/R switches are on, and delays driver stage
and T/R switch shutdown until the PA module has ramped down in power. This prevents
“keyclicks” from abrupt transmitter turn-on and turn-off.
12.3
Controller CCA, A2
The Controller CCA uses a Motorola microprocessor (
µ
P), U1, to process and control
information for the radio modem. The in circuit serial programming (ICSP) connector,
J5, is used only at the factory to install the boot loader program. The
µ
P has flash
memory that can be updated through the Serial I/O port, J9.
The
µ
P, U1, communicates with the Serial I/O port, J9, via RS232 transceiver, U5. The
Serial I/O port, J9, is used to communicate with the
µ
P, U1, via a RS232 cable to a PC
running any communications program, such as HyperTerminal™ in Windows™.