User Manual
Table Of Contents
- 1GENERAL
- 1.1Introduction
- 1.2Performance Specification
- 2THEORY OF OPERATION
- 2.1Amplifier Operation
- 2.2Power Requirements
- 2.3RF Circuitry
- 2.3.1VT-3/150 Lowpass Filter
- 2.4Power Control Circuitry
- 2.5Power Sensing Circuitry
- 2.5.1Output Power Sense
- 2.5.2VSWR Sense
- 2.5.3VSWR Overload
- 3VT-3/150 AMPLIFIER ALIGNMENT
- 3.1General
- 3.2Repair Note
- 3.3Recommended Test Equipment List
- 3.4Printed Circuitboard Numbering Convention
- 3.5Standard Factory Settings and Jumper Configuration
- 3.6VT-3/150 AmplifierAlignment
- 3.6.1General
- 3.6.2VT-3/150 Amplifier Adjustment
- 3.6.2.1General Set-Up
- 3.6.2.2Output Power Alarm (Forward Power)
- 3.6.2.3Output Power
- 3.6.2.4Antenna VSWR Alarm (Reverse Power)
- 3.6.2.5Antenna VSWR Overload
- 3.6.2.6Procedure Verification
- 4ILLUSTRATIONS AND SCHEMATIC DIAGRAMS
- 4.1VT-3/150 VHF Amplifier Component Layout
- 4.2VT-3/150 VHF Amplifier Schematic Diagram
- 4.3VT-3/150 VHF Lowpass Filter Component Layout
- 4.4VT-3/150 VHF Lowpass Filter Schematic Diagram
- 5PARTS LISTS
- 5.1VT-3/150 Amplifier Electrical Parts List
- 5.2VT-3/150 Low Pass Filter Electrical Parts List
- 5.3VT-3/150 Amplifier Mechanical Parts List
- 6REVISION HISTORY
DE
DANIELS
ELECTRONICS
2-4
VHF Amplifier Instruction Manual VT-3 132 - 174 MHz
4
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.