Assembly Instructions Chapter 4
4-6 kW UHF Translator Chapter 4, Circuit Descriptions
837B, Rev. 0 4-42
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
100 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
100 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, which are connected to the
inputs of the (A5-A2, A5-A3, A5-A4 &
A5-A5) amplifier modules.
4.7.10 (A5-A2 to A5-A5) LDMOS
Amplifier Assemblies (1301556;
Appendix D)
The outputs of the splitter assembly are
fed to the inputs of the four LDMOS
amplifier assemblies. Each of the
LDMOS amplifier assemblies is made up
of a (51-5379-309-00) module that
operates class AB. The module is a
broadband amplifier for the frequency
range of 470 to 860 MHz. The
amplification is approximately 13 dB.
The amplification circuit consists of the
parallel connected push-pull amplifier
blocks V1 and V2 operating in class
AB. In order to match the transistor
impedance to the characteristic
impedance of the input and output
sides, matching networks are placed
ahead and behind the amplifier blocks.
Transformers Z3 to Z6 serve to
balance the input and output signals.
The paralleling circuit is achieved with
the aid of 3 dB couplers Z1 and Z2.
The working point setting is factory
implemented by means of
potentiometers R9, R11 and R12 and
should not be altered.
The output of the four LDMOS amplifier
modules are connected to (A5-A6) the
4 way combiner assembly.
4.7.11 (A5-A6) 4-Way Combiner
Assembly (1301557 [CH. 14 to
26], 1301558 [CH. 27 to 43], and
1301559 [CH. 44 to 69]; Appendix
D)
The 4-way combiner assembly contains
(A5-A6-A1) a 4-way combiner board,
(A5-A6-A2) a circulator, (A5-A6-A3) a
thermal switch and (A5-A6-A4) another
thermal switch.
The 4-way combiner board is made up
of three, 2-way Wilkinson stripline
combiners. Two of the RF inputs to the
board are soldered directly to the
inputs for the 2-way combiner that
contains R5. R5 is a balancing resistor
in which any RF due to mismatching in
the combiner will be dissipated. The
other two RF inputs are soldered
directly to the 2-way combiner that
contains R6. R6 is a balancing resistor
in which any RF due to mismatching in
the combiner will be dissipated. The
outputs of the two, input 2-way
combiners connect to the third 2-way
combiner that contains R7. R7 is a
balancing resistor in which any RF due
to mismatching in the combiner will be
dissipated. The output of the third
combiner is connected to the output of
the 4-way combiner board that is
cabled to an external circulator.
The circulator protects the tray from
high-reflected power. A directional
coupler is built into the RF output
circuit on the 4-way combiner board.
The coupler provides a forward power
sample at J1 that is -40 dB down from
the level of the RF output signal.
A reject power sample from the
circulator is fed to the reject sample
input jack J2 on the 4-way combiner
board that is terminated into a 50-Ω
load. A directional coupler is built into
the reject sample circuit that provides
at J3 a signal that is -40 dB down from
the level of the reject power sample.
Both the reject and forward samples
are fed to (A6) the dual peak detector
enclosure.