Specifications
TRANSMIT RECEIVE SWITCH
When the transmit 13.6 Volt line (Pin 3 of J301) be-
comes active, current passes through L316, R308, L311,
CR301, L315, CR302 and CR303 to ground. L316, C340,
C339, L311 and C338 isolate and bypass the RF. CR301
conducts RF from Q303 to the low pass filter. CR302 and
CR303 short to ground preventing RF from entering the re-
ceiver input P303. L315 along with the distributed capaci-
tance form a high impedance path to ground, thus
preventing loss of transmit power.
During receive CR301 opens, disconnecting Q303.
CR302 and CR303 open, removing the short from the re-
ceiver path. L315, along with the distributed capacitance,
then forms a low pass pi section that passes the signal from
the antenna to the receiver input.
DC POWER DISTRIBUTION
DC power enters the PA Assembly from the power cable
assembly which is plugged into P301. The four leads in this
cord are:
1. Red, Pin 1 = (+) or 13.6 VSW
2. Black, Pin 2 = (–) or Ground
3. Orange, Pin 3 and 4; Jumper between Pin 3 and 4
to 13.6 VSW
The Black wire should go directly to the negative termi-
nal of the power supply module. The Red wire goes directly
to the positive terminal of the power supply module.
The Red wire, or high current path, goes directly to
Q303, Q302 and Q301 through L317 and R306. C329 by-
passes the RF. CR305 protects this line from polarity rever-
sal by blowing the fuse.
13.6 VSW enters at P301. CR304 protects this line
against polarity reversal. This 13.6 VSW line is connected to
the Main Board through the power interconnect cable and
Pin 1 of J301. This line is bypassed by C326 and C328. The
other pin connect of J301 is Pin 4 (ALC OUT), the sensing
voltage for thermal shut down and power leveling circuits.
A switched 13.6 volt source from Q505 supplies voltage
to the transmit receive switch. This voltage operates the TR
switch through line limiting resistor R308. This line sup-
plies 13.6V to U301, the 8V regulator, and is bypassed by
C325.
RF POWER LEVELING AND THERMAL
SHUTDOWN
L318 and R310 form an RF pickup loop that samples
relative output power. This sampled output is rectified by
CR307 and filtered by C331, R309, R307 and C342.
Q305’s bias is set by variable resistor R317. The detected
output interacts with this variable DC voltage. R317 is used
to set Q305’s collector (the RF drive control line) to 4.3V at
45 Watts RF output. Any decrease in output power will
lower the detected voltage of CR307 causing Q305’s collec-
tor voltage to increase. This increased voltage is applied to
the ALC circuitry (on the Main board) which will increase
the exciter output power bringing the PA output power back
up to 45 Watts output. Any increase in the 45 Watts output
will have an opposite effect.
Q304 and RT301 form a temperature sensing circuit
with RT301 thermally connected to Q303. When Q303’s
case exceeds +90°C, Q304 will start to conduct which in
turn will increase the gain of Q305. Q305’s collector volt-
age will then be lower, causing the exciter output to de-
crease. This results in lower drive to the power amplifier,
allowing it to cool. RF output power is decreased but still al-
lows lower power operation. C343 is a RF bypass.
POWER SUPPLY MODULE
The power supply module converts 120 volts or 220
volts at 50 Hz or 60 Hz to 13.8 volts DC. The power supply
is a switch mode type which operates at high efficiency to
keep internal temperatures low.
REAR PANEL DB-15 CONNECTOR
I/O SPECIFICATIONS
The function, description and specifications of each pin
of the Multifunction Port’s connector is as follows:
Pin Number: 1
Name: GND
Description: Chassis and circuit ground. This point
serves as the voltage reference for the sig-
nals on all of the other pins.
Pin Number: 2
Name:
REMOTE PTT
AE/LZB 119 1882 R1B
15