User's Manual

Digital UHF Transmitter Chapter 4, Circuit Descriptions
DT835A, Rev. 1 4-1
Chapter 4
Circuit Descriptions
4.1 (A1) UHF Exciter Assembly
The (A1) UHF Exciter Assembly
contains (A1) a UHF Exciter Tray
(1142445), (A4 & A5) two Variable
Gain/Phase Trays (1245-1200), (A6) a
Metering Panel (1061456), (A8) an AC
Distribution Assembly, Exciter (1245-
1500) and (A9) a Remote Interface
Assembly (1061198).
The (A1) UHF Exciter Tray (1142445),
takes the Digital IF Input that is
upconverted to the On Channel RF by
mixing it with a L.O. signal generated
by the Channel Oscillator Assembly.
The RF Output of the UHF Exciter at J15
connects to (A3) a Splitter which splits
the RF two ways with the RF Output #1
connected to the input of the (A5)
Variable Gain/Phase Tray (1245-1200)
and the RF Output #2 connected to the
input of the (A4) Variable Gain/Phase
Tray (1245-1200). The output of the
(A4) Variable Gain/Phase Tray connects
to (A2) the Side A Amplifier Assembly
(1278-1300). The output of the (A5)
Variable Gain/Phase Tray connects to
(A3) the Side B Amplifier Assembly
(1278-1300).
4.1.1 Control and Status
The Control and Status of the
Transmitter are provided by the Meter
indications on the Metering Panel and
the Variable Gain Phase Trays. There
are also Control, Status and LED
Indications located on the front panel of
the UHF Exciter Tray. The switches and
LED indicators, which are mounted so
that the switches and LEDs are
operated or viewed from the front
Panel of the UHF Exciter, are part of the
Transmitter Control Board (1245-
1101). On the UHF Exciter Tray, switch
(S1) is an Operate/Standby Switch that
provides the Operate Commands
(Enables), when in Operate, to each of
the Amplifier Arrays. The Enable is
needed to turn on the Switching Power
Supplies located in each of the UHF
Amplifier Trays. When the UHF Exciter
is in Operate, the Green LED (DS2) is
On and when in Standby the Amber
LED (DS1) is On. NOTE: If the
Transmitter does not switch to Operate,
when S1 is switched to Operate, check
that a Dummy Jumper Plug is
connected to Jack J7, with a Jumper
between Pins 1 & 2, located on (A9) the
Remote Interface Assembly in the
Single UHF Exciter Assembly. The
Jumper provides the Interlock to the
UHF Exciter needed for the operation of
the Transmitter. If the Interlock is
present, the Green LED (DS5), located
on the Transmitter Control Board,
should be lit.
Operation of the Transmitter is
controlled by the front panel switches
located on the UHF Exciter Tray.
During Normal operation of the
Transmitter, Switch S2 should be in the
Auto position. The front panel of the
UHF Exciter also has LEDs that indicate
a Input Fault (Loss), Red LED (DS9)
and a VSWR Cutback, Amber LED
(DS7).
4.1.2 Digital Input and Remote
Connections
The Digital Input to the Transmitter,
connects to the (A9) Remote Interface
Panel located on the rear of the Single
UHF Exciter Assembly. The Digital
Input connects to Jack J2 that is cabled
to J2 on the DM8-R Modulator.
Remote Monitoring and Operation of
the Transmitter is provided through the
Jacks (J8, J9 & J10) located on (A9) the
Remote Interface Assembly mounted
toward the rear of the Single UHF
Exciter Assembly. Jack (J7) should
have a dummy plug connected to it,