User's Manual

Digital UHF Transmitter Chapter 4, Circuit Descriptions
DT835A, Rev. 1 4-35
sensitive to changes in the video level.
A sample of the forward power is
tapped off by R6 and R8 and fed to J3,
the forward sample output jack. Diode
CR2 provides temperature
compensation for diode CR1. An input
signal level of approximately +17 dBm
is enough to give a 1-VDC level at the
output of U1C.
A reflected output power sample enters
the board at SMA jack J2. Resistors
R18, R19, and R20 form an input
impedance-matching network of 50Ω.
The reflected power signal is then
detected by CR3, R21, R22, R24, C5,
and C6 and the output is buffered by
operational amplifiers U3A and U1B
before it is connected to reflected
power output jack J4-2. U3 has a very
high input impedance that makes the
IC less sensitive to changes in the
video level. Diode CR4 provides
temperature compensation for diode
CR3. An input signal level of
approximately +17 dBm is enough to
give a 1-VDC level at the output of
U1B.
The +12 VDC needed for the operation
of U1 on the board is generated from
the +28 VDC which enters at J4, pin 7.
The +28 VDC is fed to U2, a voltage
regulator IC, that produces +12 VDC at
its output, which is connected to U1.
4.8.8 (A5-A1) 4-Way Splitter
Assembly (1265-1432; Appendix D)
The 4-way splitter assembly contains
(A5-A1-A1) a 4-way splitter board
(1227-1312) 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, which are connected to the inputs
of the external amplifier boards.
4.8.9 (A5-A1-A1) 4-Way Splitter
Board (1227-1312; 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.
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.
4.8.10 (A4-A3, A5-A2, A5-A3, A5-
A4, A5-A5) Dual Stage Amplifier
Assemblies (1265-1413 and 1265-
1439, low band/1265-1411 and
1265-1440, mid band/1265-1420
and 1265-1441, high band;
Appendix D)
4.8.10.1 Low Band
The dual stage UHF amplifier assembly,
Class AB, low band is made using a