User's Manual

300-Watt Digital UHF Transmitter Chapter 4, Circuit Descriptions
DT830A, Rev. 1 4-33
The output connects to J2 on the board.
A sample of the output is detected by
CR10 and connected to TP4. A DVM can
be connected to TP4 to give a voltage
indication of the RF output level.
The +26 VDC connects to the board at
J3-3 and is split, with one half connected
to the two, class A amplifier circuits. The
other half of the +26-VDC input is
filtered, isolated by L4 and C13, and
connected to U1. U1 is a +12-VDC
regulator IC that produces the +12 VDC
needed to operate the ICs on the board.
4.3.16 (A5-A6) 4-Way Combiner
Assembly; Appendix D)
The 4-way combiner assembly contains a
4-way combiner board. 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 of a 2-way
combiner that contains R5. R5 is a
balancing resistor that dissipates any RF
due to mismatching in the combiner. The
other two RF inputs are soldered directly
to a 2-way combiner that contains R6. R6
is a balancing resistor that dissipates any
RF due to mismatching in the combiner.
The outputs of the two input 2-way
combiners connect to a third 2-way
combiner that contains R7. R7 is a
balancing resistor that dissipates any RF
due to mismatching in the combiner. The
output of the third combiner is connected
to the output of a 4-way combiner board
that is cabled to an external circulator.
A directional coupler is built into the RF
output circuit on the 4-way combiner
board to provide 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 reject sample input jack J2 on
the 4-way combiner board. A directional
coupler is built into the reject sample
circuit to provide a signal at J3 that is -40
dB down from the level of the reject
power sample.