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
2-2
VHF Amplifier Instruction Manual VT-3 132 - 174 MHz
2
2.3 RF Circuitry
The RF
circuitry
consists of several blocks: a 7 dB input pad (R1, R2, and R3), an RF
amplifier
module
(U4),
an output power boosting transistor (Q7), three
directional
couplers (TL1, TL3, and
TL4), and the
VT-3/150
Lowpass Filter. The heart of the
VT-3/150
Amplifier
is RF
amplifier
module
U4.
The output of U4 is further
amplified
by Q1 to a
maximum
of 8.0 Watts at the
antenna
connector. The frequency band of the
VT-3/150
Amplifier
is
determined
by the
operating
frequency
range of the RF
amplifier
module
U4.
Directional
couplers (TL1, TL3, and TL4) are used to
sample forward and reverse
power.
The sampled power is used by the sensing and power control
circuits
to control the amplifier's operation. The final step in the RF path is output
filtering
and, as
mentioned
earlier, this is done by the
VT-3/150
Lowpass Filter.
2.3.1
VT-3/150 Lowpass Filter
The
VT-3/150
Lowpass
Filter
is a 50 ohm, 9 pole,
reciprocal
filter
with a 3 dB cutoff frequency of
approximately
185 MHz. The lowpass
filter
assembly
attenuates
the desired
signal's
harmonics as
well as any other out-of-band emissions so that a
'clean'
RF signal is output to the
antenna
connector.
2.4
Power Control Circuitry
The
VT-3/150
Amplifier
employs a closed loop power control which uses a sample of the forward
RF power to control the gain of RF
amplifier
U4.
Op-amp
U1b compares the sampled RF
voltage
to the output power
setpoint
and
generates
an error signal which Q3 uses to control the
voltage
on
U4's
gain control pin. The output power
setpoint
is
determined
by R7, the
Output
Power
Adjust
potentiometer.
The forward power is sampled by TL1, D5, C14, R13, L6, R12, and C15. The power control
circuitry
keeps the output power of U4 constant.
Therefore
the amplifier's output power will
fluctuate
with
variations
in the
+13.8
Vdc supply voltage.