Page 48 of 101
DWG ID: 181-0101-00A
Date: 2003-09-26
When driven by +13 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 L115 and L116, and C169 through C173.
To isolate the PA module from the receiver, an electronic T/R switch is used. The switch
is formed around PIN diodes CR103 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 CR103
protects and isolates the receiver input when the radio is in transmit.
12.1.3
Miscellaneous Functions
Two on-board regulators are used to provide the 5 V dc used by most of the circuitry in
the radio. IC107 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. IC108 is an identical
regulator, which supplies voltage to those circuits that are to be powered-up only in
receive. The regulator is enabled through IC106E and F by the RX-EN (J012-4) input.
The transmitter PA module driver stages and the T/R switch are powered by +7.2 V
through Q113. The TX-EN (J102-3) input through delay and sequencing circuitry
formed around IC106, Q112, and Q114 enable Q113. 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.
12.2
Ritron’s UHF Radio XCVR, A1A1
12.2.1
Receiver
12.2.1.1
RF Amplifier and Band-pass Filters
The incoming RF signal from the input connector J101 passes backward through the
transmitter low-pass filter and the electronic T/R switch to a two-pole band-pass filter
formed around L101 and L102. This filter is of Cohn type with 1.5 dB insertion loss and
a bandwidth of 25 MHz. This filter is followed by a low noise amplifier stage formed
around Q101. This amplifier has a gain of about 17 dB with a noise figure of 2 dB, and
serves to amplify the incoming RF signal above the noise of the following stages.
Following this stage is a four-pole Cohn filter formed around L103 through L106. This
filter has an insertion loss of 4 dB and a bandwidth of 25 MHz. The two filter sections