Codan Radio Communications VT-3-150-SN User Manual
VHF Amplifier Instruction Manual VT-3 132 - 174 MHz
2-1
2
THEORY OF OPERATION
2.1
Amplifier Operation
A power control circuit monitors the RF output power of amplifier U4 and keeps the power
constant. The output power from the high power amplifier will change as the unregulated +13.8
Vdc supply varies. Note that the frequency band does not change how the amplifier operates; it only
changes a few component values in the RF circuitry.
constant. The output power from the high power amplifier will change as the unregulated +13.8
Vdc supply varies. Note that the frequency band does not change how the amplifier operates; it only
changes a few component values in the RF circuitry.
Power for the VT-3/150 Amplifier is provided from the MT-3 Transmitter Board. The +13.8 Vdc
supply (if required) is continuously connected to the amplifier; whereas, the +9.5 Vdc supply is
always switched by the transmitter's PTT circuitry. The VT-3/150 Amplifier will not use any power
from the +13.8 Vdc supply until the amplifier's +9.5 Vdc line is switched on and an RF input
signal is present. The synthesizer or crystal control module controls the +9.5 Vdc to the amplifier's
circuitry; switching it on by grounding the amplifier's input enable line. The synthesizer or crystal
control module will ground the input enable line only when the RF signal from the synthesizer or
crystal control module is phase locked. This prevents unwanted spurious emissions during
transmitter start-up. A typical start-up sequence is shown below:
supply (if required) is continuously connected to the amplifier; whereas, the +9.5 Vdc supply is
always switched by the transmitter's PTT circuitry. The VT-3/150 Amplifier will not use any power
from the +13.8 Vdc supply until the amplifier's +9.5 Vdc line is switched on and an RF input
signal is present. The synthesizer or crystal control module controls the +9.5 Vdc to the amplifier's
circuitry; switching it on by grounding the amplifier's input enable line. The synthesizer or crystal
control module will ground the input enable line only when the RF signal from the synthesizer or
crystal control module is phase locked. This prevents unwanted spurious emissions during
transmitter start-up. A typical start-up sequence is shown below:
1) the transmitter is keyed on (+13.8 Vdc is always present)
2) +9.5 Vdc is switched on by the PTT circuitry and the synthesizer
2) +9.5 Vdc is switched on by the PTT circuitry and the synthesizer
or crystal control module PTT line is pulled low
3) an RF signal is output to the amplifier
4) the amplifier's input enable line is activated
5) the amplifier outputs RF power
4) the amplifier's input enable line is activated
5) the amplifier outputs RF power
2.2
Power Requirements
Typical current requirements for the VT-3/150 Amplifier at different power levels are given in the
Table 2-3 below. The current drawn from the +9.5 Vdc supply should never exceed 1.2 Amps and
the current drawn from the +13.8 Vdc supply should never exceed 1.5 Amps.
Table 2-3 below. The current drawn from the +9.5 Vdc supply should never exceed 1.2 Amps and
the current drawn from the +13.8 Vdc supply should never exceed 1.5 Amps.
Table 2-1
VT-3/150 Amplifier Current Consumption
Output
Power
+9.5 Vdc
Supply Current
+13.8 Vdc
Supply Current
2.0 W
0.64 A
0.51 A
4.0 W
0.79 A
0.75 A
6.0 W
0.89 A
0.93 A
8.0 W
1.04 A
1.10 A
Note: Current consumption measured at 153 MHz