User's Manual

300-Watt Digital UHF Transmitter Chapter 4, Circuit Descriptions
DT830A, Rev. 1 4-24
frequency of the channel of operation,
the assembly has approximately 9 dB of
gain.
The RF input to the assembly connects to
SMA jack J1. The amplified RF output of
the assembly is at SMA jack J2. Typically,
with an input signal of +21 dBm at J1 of
the assembly, an output of +30 dBm can
be expected at J2.
The +28-VDC bias voltage connects
through FL1, an RF bypass feed-through
capacitor, that is mounted on the
amplifier assembly to E1 on the board.
4.3.2 (A3-A1) 1-Watt Amplifier
Board (1227-1303; Appendix D)
The 1-watt UHF amplifier board is part of
the 1-watt UHF amplifier assembly
(1227-1319) and provides approximately
+10 dB of gain.
The UHF signal enters the board at J1, an
SMA connector, and is applied through
coupling capacitor C1 and a stripline
circuit to Q1, a UTV040F UHF wideband-
amplifier device. The base and collector
voltages needed to operate the transistor
are obtained from the +26.5 VDC line
that connects to the board at E1. The
collector voltages fed through VR1, VR2,
R3, and R4 and the base voltages fed
through R2 and R1. The amplified UHF
output of Q1 is coupled through a
stripline circuit and C14 to J2, the output
SMA jack of the board.
The board is powered by the +26.5 VDC
that is produced by an external power
supply in the tray. The +26.5 VDC enters
through E1 and is fed across R4 and R5,
which drops approximately 6 volts, to the
collector (+20 VDC). The voltage is
filtered by RF decoupling components L4,
C11, C12, and C15 before it is connected
to the collector. The bias voltage is
connected across R3, VR1, VR2, R1, and
R2, which sets the base bias voltage at
+.8 VDC and forward biases Q1. C6, L1,
and L2 provide RF decoupling of the bias
voltage before it is connected to the
base.
The board has a self-bias protection
circuit that uses zener diodes VR1 and
VR2. If the current draw of the device
increases, the voltage drop across R4
and R5 increases; this decreases the
voltage that is applied to VR1 and VR2.
These two diodes drop a fixed voltage of
20 VDC across them. As a result, if the
voltage drop across R4 and R5 increases,
the voltage available to the base of Q1
decreases and will eventually shut off the
device.
4.3.3 (A5-A1) 4-Way Splitter
Assembly ( Appendix D)
The 4-way splitter assembly contains a
4-way splitter board that is made up of
three 2-way Wilkinson stripline splitters.
One RF input to the board provides four,
equal RF outputs.
The RF input to the board is connected to
the input of the first 2-way splitter that
contains R1. R1 is a balancing resistor in
which any RF due to mismatching in the
first splitter will be dissipated. One of the
two outputs from the splitter connects to
another 2-way splitter that contains R2.
R2 is a balancing resistor in which any RF
due to mismatching in the splitter will be
dissipated. The other output of the first
splitter connects to the third 2-way
splitter that contains R3. R3 is a
balancing resistor in which any RF due to
mismatching in the splitter will be
dissipated. The two output splitters
provide four, equal RF outputs, two each,
that are connected to the inputs of the
external amplifier boards.
4.3.4 4-Way Splitter Board
(Appendix D)
The 4-way splitter board is made up of
three 2-way Wilkinson stripline splitters.
One RF input to the board provides four,
equal RF outputs.