2-4
VHF Amplifier Instruction Manual VT-3 132 - 174 MHz
2.5.3
VSWR Overload
The VSWR overload circuit protects the VT-3/150 Amplifier from excessive antenna VSWR by
reducing the amplifier's gain (output power) when an overload condition occurs. The VSWR
overload circuit (R14, R37, R39, R40, U2a, and Q6) is an extension of the VSWR sense circuit and
operates the same as the VSWR sense open collector circuit. The VSWR Overload Adjust
potentiometer (R37) reduces the voltage level of the VSWR Alarm Setpoint. The voltage set by
R37 is the compared to the output power alarm setpoint by op-amp U2a which then drives
transistor Q6. When transistor Q6 turns on, signaling an overload condition, resistor R14 is
grounded which reduces the output power setpoint. Reducing the output power setpoint lowers the
VT-3/150 Amplifier's gain and protects the amplifiers from excessive current draw resulting from
high antenna VSWR.
The VSWR overload circuit's range of adjustment depends on the setting of the VSWR Alarm
Adjust potentiometer (R36). The VSWR overload transistor Q6 can be activated at the same point
at which the VSWR alarm becomes active or the VSWR overload circuit can be disabled by turning
R37 completely counterclockwise.
Summary of Contents for VT-3/140-SWA2
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