User's Manual

Digital UHF Transmitter Chapter 4, Circuit Descriptions
DT835A, Rev. 1 4-44
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.
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 reject sample input
jack J2 on the 4-way combiner board. A
directional coupler is built into the
reject sample circuit that provides J3
with a signal that is -40 dB down from
the level of the reject power sample.
NOTE: Your Transmitter will contain
either a 1278-1200 Single Phase or a
1278-1100 Three Phase AC Distribution
Assembly.
4.9 (A10) AC Distribution
Assembly, Single Phase (1278-
1200; Appendix C)
The AC Distribution Assembly, Single
Phase, Amplifier Assembly (1278-1200)
distributes the Main AC Input, 208/240
VAC @ 100 Amps, to the individual
Trays in the Amplifier Cabinet which
make up the Amplifier Array.
The 208/240 VAC Single Phase Main AC
Input to the Amplifier Cabinet connects
to the Terminal Block TB1, Line 1 to
TB1-1A, Line 2 to TB1-3A and Safety
Ground to TB1-4A.
The 208/240 VAC Main AC Input is
wired from the Terminal Block TB1-1B
(Line 1) to the 100 Amp Circuit Breaker
CB1-1 and TB1-3B (Line 2) to the
Circuit Breaker CB1-5. The switched
Main AC Input is wired from the main
circuit breaker to the up to six 20 Amp
Circuit Breakers, CB2-CB7, that
distribute the AC to the up to six UHF
Amplifier Trays in the Amplifier Array
and two 3A circuit breakers CB8 and
CB9 which connect the AC to the Fan
(A12-A3) mounted on the Reject Load
Assembly. The number of 20 Amp
circuit breakers is determined by the
number of Amplifier Trays which is
determined by the output power of the
Transmitter in which the Amplifier
Assemblies are used. Four circuit
breakers, CB2-CB5, are needed for a 4
kW Transmitter, five circuit breakers,
CB2-CB6, are needed for a 5 kW
Transmitter and six circuit breakers,
CB2-CB7, are needed for a 6 kW
Transmitter. Three MOVs, for surge
and transient protection, are connected
to the AC Lines from the Circuit
Breaker. VR4 and VR6 connect from
the AC Lines to Ground and VR3
connects across the AC Lines.
CB2 is a 20 Amp Circuit Breaker which
protects the AC connected through J1
on the AC Distribution Assembly to J4
on the (A1) UHF Amplifier Tray. CB3 is
a 20 Amp Circuit Breaker which
protects the AC connected through J2
on the AC Distribution Assembly to J4
on the (A2) UHF Amplifier Tray. CB4 is
a 20 Amp Circuit Breaker which
protects the AC connected through J3
on the AC Distribution Assembly to J4
on the (A3) UHF Amplifier Tray. CB5 is
a 20 Amp Circuit Breaker which
protects the AC connected through J4
on the AC Distribution Assembly to J4
on the (A4) UHF Amplifier Tray. CB6