User Manual

DE
DANIELS
ELECTRONICS
UHF Amplifier Instruction Manual UT-3 406 - 512 MHz 2-1
2 THEORY OF OPERATION
2.1 Amplifier Operation
The operation of the UT-3/400 Amplifier varies slightly according to whether the amplifier is a low
power (0.5-2.0 W) or a high power (2.0-8.0 W) version. The low power amplifier does not use
transistor Q1 to boost the output power; consequently, it does not require the +13.8 Vdc supply.
In both versions the power control circuitry monitors the RF output power of amplifier U4 and
keeps the power constant. Therefore, 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 UT-3/400 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 UT-3/400 Amplifier will not consume any
power from the +13.8 Vdc supply until +9.5 Vdc is switched on for the amplifier's circuitry 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 will ground the input enable line only when the synthesizer's RF signal is phase
locked. This prevents unwanted spurious emissions during transmitter start-up. A typical start-up
sequence is listed below:
1) +13.8 Vdc is always present
2) the transmitter is keyed on
3) +9.5 Vdc is switched on by the PTT circuitry and the synthesizer
or crystal control module PTT line is pulled low
4) an RF signal is output to the amplifier
5) the amplifier's input enable line is activated
6) the amplifier outputs RF power