Technical Manual

GUARDIAN VHF 110W MOBILE 2-15
2.6.2.1 Voltage Regulator and 7.8V On/Off Switch
Linear regulator U5 provides +7.8V to the RF power control circuitry and to the other two PC assemblies in the
control head. The regulator is powered via Q10 body diode at all time. When the unit is turned off all the circuits
are disconnected from power except the transceiver in the control head. The transceiver in this case is in the off
state. The power consumption in this case is less than 2 mA powering the boat backup memory circuits.
2.6.3 Communication with Transceiver
Twenty pin IDC headers J2 and J3 carry control and status signals from the transceiver and front panel via the
Control PCA.
2.6.4 Audio Amplifiers
The board contains two identical audio amplifiers. Each audio amplifier has 20 dB gain and is capable of delivering
more than 10W to a 4-ohm load in a bridge-tied-load configuration. They are fed from the transceiver audio output.
A front panel switch selects either or both amplifiers; an unselected amplifier is placed in a mute condition by the
appropriate disable signal. When there is no received signal, both amplifiers are placed in a low-current standby
mode by squelch comparator.
2.6.5 Power Levels Detector, Converter, and RF/DC Combiner
ON /OFF, PTT and RF output power control signals to the 110W power amplifier are generated on this board.
These are present as DC signals on the center conductor of the coaxial cable connecting the control head to the
remote RF PA. A low-pass filter prevents RF from reaching the control circuitry. The voltage levels are as follows:
DC Control Voltage Range PA State
0 to 0.4V DC on/off switch – OFF
>0.7V DC on/off switch – ON
0.7 to 1.2V PA is in bypass – RECEIVE mode
2.1V Power output set 25W
3.6V Power output set 50W
6.5V Power output set to 110W
The transceiver power levels are detected via the connection to TP21. The voltages are as follows:
TP 21 Control Voltage Boat Power Output
2.85 5W
1.87 2W
1.28 1W
The control circuits converts an input above 2.2V (5W setting) to a control signal to 6.5V, which results in 110W
generated in the remote RF power module. Accordingly it converts the 2W and 1W control levels to the indicated
PA control. Input control of less than 1V is converted to 2.6V. The PA puts out 25W also for the 0.5W input power
setting but will fail to do so at the 0.1W setting. In this case power output is not specified, and the red LED will not
light.