User's Manual

Digital UHF Driver/Transmitter Chapter 4, Circuit Descriptions
LX Series, Rev. 1 4-17
4.4.1: (A1) 1-Watt UHF Module
Assembly (1302891; Appendix A)
The 1-watt UHF module assembly
provides radio frequency interference
(RFI) and electromagnetic interference
(EMI) protection, as well as the heatsink,
for the 1 watt UHF amplifier board
(1302761) that is mounted inside the
assembly.
The +12-VDC bias voltage connects
through J5, a RF-bypassed, feed-through
capacitor, to the amplifier board. The
-12-VDC bias voltage connects through
J6, a RF-bypassed, feed-through
capacitor, to the amplifier board. E1 on
the assembly connects to Chassis
ground.
4.4.2: (A1-A1) 1 Watt UHF Amplifier
Board (1302761; Appendix A)
The 1 watt UHF amplifier board provides
approximately +17 dB of gain. Typically,
in a 500 or 1kW system with an input
signal of +3 dBm at J1 of the assembly, an
output of +20 dBm can be expected at J2.
The UHF signal enters the board at J3, a
SMA connector, and is applied to U3 an IC
hybrid coupler assembly that splits the
input signal into two equal parts. The two
amplifier paths are identical using Q4 and
Q5, 1-Watt HFETs as the amplifier devices.
Each HFET has approximately 14 dB of
gain. The drain voltage needed to operate
each HFET is obtained from the +12 VDC
line that connects to the board at J5 and is
regulated down to +8.25 volts by U4. The
gate negative bias voltage is obtained from
the -12 VDC line that connects to the
board at J6. The amplified outputs of the
HFETs are applied to U2 an IC hybrid
coupler assembly that combines the
amplified signals into a single output that
connects to J4 of the board.
Figure 4-1: RF Amplifier Assembly Module