Assembly Instructions Chapter 4

4-6 kW UHF Translator Chapter 4, Circuit Descriptions
837B, Rev. 0 4-41
amplifier assembly is made up of a (51-
5378-308-00) module, which is a class
AB module that is a highly linear
broadband amplifier for the frequency
range of 470 to 860 MHz. It can
deliver an output power of 40 watts
(CW) at an amplification of
approximately 13 dB.
The amplification circuit consists of
LDMOS transistors V804 and V805
connected in parallel and operating in
class AB. The paralleling network is
achieved with the aid of 3 dB couplers
Z802 and Z803. A further 3 dB coupler
Z801, in conjunction with capacitors
C800 and C819, serves as a phase
shifter. Phase alignment (for the
complete amplifier), as well as
quiescent current setting by means of
potentiometers R807 and R808. It is
factory implemented and should not
be altered.
PIN diodes V810/V811 form a
variable-damping circuit that is used to
adjust the amplification of the 40-watt
module. The adjustment is performed
with the Gain potentiometer R838. A
readjustment of the amplification may
be required, e.g., after repair work, to
ensure that all amplifiers in a
translator deliver the same output
power
4.7.7 (A4-A2) Coupler Board
Assembly (1227-1316;
Appendix D)
The UHF coupler assembly is mounted
in the A4 amplifier enclosure and
provides a forward power sample of the
input drive level to the (A4-A3) LDMOS
amplifier assembly. The drive-level
sample from J3 is cabled to the
amplifier control board where it
connects to the input of the overdrive-
protection circuit.
The RF input to the UHF coupler
assembly, from the 40 Watt UHF
amplifier module, connects to SMA jack
J1. The RF is connected by a stripline
track to SMA output jack J2. A hybrid-
coupler circuit picks off a forward
sample that is connected to SMA type
connector jack J3. R1 is a dissipation
load for the reject port of the coupler.
4.7.8 (A4-A3) LDMOS Amplifier
Assembly (1301556; Appendix D)
The output of the coupler assembly is
fed to (A4-A3) the LDMOS amplifier
assembly. The LDMOS amplifier
assembly 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 (A4-A3) LDMOS
amplifier module is connected to (A5-
A1) the 4 way splitter board.
4.7.9 (A5-A1) 4-Way Splitter
Assembly (1301580;Appendix D)
The 4-way splitter assembly 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 100 
balancing resistor in which any RF due