Assembly Instructions Chapter 4

4-6 kW UHF Translator Chapter 4, Circuit Descriptions
837B, Rev. 0 4-40
VDC needed to operate the ICs on the
board.
The output of the variable gain/phase
board (+19 dBm) at J2 connects
through A16 a 6dB pad to J1 (+13
dBm) on the 1 Watt amplifier board
assembly.
4.7.3 (A3) 1-Watt Amplifier Board
Assembly (1301546; Appendix D)
The 1-watt UHF amplifier board
assembly provides radio frequency
interference (RFI) and electromagnetic
interference (EMI) protection, as well
as the heatsink, for the 1-watt UHF
amplifier board, 32V (1301547) that is
mounted inside the assembly.
Depending on the 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 +13
dBm at J1 of the assembly, an output
of +22 dBm can be expected at J2.
The +32-VDC bias voltage connects
through FL1, a RF-bypassed, feed-
through capacitor, to E1 on the
amplifier board.
4.7.4 (A3-A1) 1-Watt Amplifier
Board, 32V (1301547; Appendix D)
The 1-watt UHF amplifier board, 32V is
mounted in the 1-watt UHF amplifier
assembly (1301546) and provides
approximately +9 dB of gain.
The UHF signal enters the board at J1,
a 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 +32 VDC line that connects to
the board at E1 and is divided down to
26 volts by R4 and R5. The collector
voltage is fed through L4 and the base
voltage is fed through R3, VR1, VR2 the
divider network R1 and R2 and L2. 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 +32 VDC
that is produced by an external power
supply in the tray. The +32 VDC enters
through E1 and is fed across R4 and
R5, which drops approximately 6 volts,
to the collector (+26 VDC). The voltage
is filtered by RF decoupling components
L4, C11, C12, and C15 before it is
connected to the collector. The base
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 the device
will eventually be shut off.
4.7.5 (A1) UHF Filter (1007-1101;
Appendix D)
The UHF filter is a tunable two-section
cavity filter that is typically tuned for a
bandwidth of 6 MHz and has a loss of
-1 dB through the filter.
4.7.6 (A4-A1) 40 Watt UHF
Amplifier Assembly (1206693;
Appendix D)
The output of the UHF filter is
connected to the input J1 of (A4-A1)
the 40 Watt UHF amplifier assembly
that is mounted on (A4) the amplifier
enclosure. The (A4-A1) 40 watt UHF