UHF Analog Driver/Transmitter/
Chapter 4, Circuit Descriptions
Translator
LX Series, Rev. 3
4-20
The RF from the Upconverter Module
Assembly connects from the Upconverter
RF Output BNC Jack J23, through a cable,
to the PA RF Input BNC Jack J24, located
on the rear of the exciter/amplifier chassis
assembly.
4.6.1 (A1) 1-Watt UHF Module
Assembly (1302891; Appendix B)
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
(1302762) that is mounted inside the
assembly. The assembly has
approximately 17 dB of gain.
The RF input to the assembly connects to
SMA Jack J3. The amplified RF output of
the assembly is at the SMA Jack J4.
Typically, with an input signal of +4 dBm
at J1 of the assembly, an output of
+21 dBm can be expected at J2.
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.
4.6.2 (A1-A1) 1-Watt UHF Amplifier
Board (1302761; Appendix B)
The 1-watt UHF amplifier board is
mounted in the 1-watt UHF amplifier
assembly (1302891) and provides
approxi17 dB of gain.
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.
4.6.3 (A4-A1) 40 Watt UHF Amplifier
Assembly (1304490; Appendix B)
The output of the UHF filter is connected to
the input J1 of (A2) the 40 Watt UHF
amplifier assembly (Figure 4-1). The
assembly is made up of a (51-5378-308-
00) module, which operates class AB and 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)
with approximately 14 dB of gain.
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
settings are achieved by means of
potentiometers R807 and R808. The
settings are 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 level adjustment is
performed with the Gain potentiometer
R838. A readjustment of the amplification
may be required, after repair work, to
ensure that the Power Amplifiers in
multiple PA transmitters deliver the same
output power.
Содержание INNOVATOR
Страница 99: ...APPENDIX A LX SERIES ANALOG SYSTEM SPECIFICATIONS...
Страница 102: ...APPENDIX B DRAWINGS AND PARTS LISTS...
Страница 105: ...APPENDIX C TRANSMITTER LOG SHEET...
