User's Manual

Digital UHF Transmitter Chapter 2, System Description and
Customer Remote Connections
DT835A, Rev. 1 2-2
is located in the (Optional) (A10) 10-MHz
reference kit (1286-1108). The board
contains a high-stability crystal oscillator
that provides a 10-MHz output that is
used as reference frequency for the
transmitter. The board is mounted within
an enclosed assembly that helps to
maintain the operating temperature of
the oscillator board.
The (A13) PLL board (1286-1104) is part
of the phase lock loop (PLL) circuit, which
provides the automatic frequency control
(AFC) voltage, that connects to the VCXO
assembly, on the UHF Generator board,
and maintains the accurate output
frequency of the VCXO. The AFC is
generated by comparing a sample of the
10-MHz reference to a sample of the
VCXO frequency. The PLL board uses an
external 10-MHz signal as the reference
unless it is missing, then an internally
generated 10-MHz signal is used. A
sample of the signal from the UHF
generator board connects to SMA jack J9,
the sample input on the board. The signal
is amplified by U8 and coupled to U9, a
divide by 20/21 IC. A sample of the
signal at the output of U8 is connected to
J10, the sample output jack on the
board, which is typically connected to the
front panel of the tray.
The selected 10-MHz reference connects
to amplifier IC U1 whose output is split.
A sample of the 10-MHz reference is
cabled to jack J3, the 10-MHz output
jack, which is connected to J5 on the rear
of the tray.
If the 50 kHz from the 10-MHz reference
and the 50-kHz from the UHF generator
board become unlocked, the red Unlock
LED, lights and the Lock LED, located on
the LED display board, is extinguished.
The RF output of the UHF exciter at J15
is split two ways by the (A3) splitter.
The RF output #1 connects to the input
of (A4) one of the variable phase/gain
trays and the RF output #2 connects to
the input of (A5) the other variable
phase/gain tray. The output of the (A4)
variable phase/gain tray connects to
(A2) the side A amplifier array
assembly. The output of the (A5)
variable phase/gain tray connects to
(A3) the side B amplifier array
assembly.
2.1.2 (Optional) 10 MHz Reference
Distribution Amplifier Tray
The (Optional) 10 MHz reference
distribution amplifier tray provides a 10
MHz reference at a suitable output level
for distribution.
The system is made up of an internal 10
MHz reference source, a reference
distribution amplifier, and splitter kit(s)
without precise offset IF to distribute the
reference signal to each transmitter.
The reference distribution amplifier tray
utilizes an internal 10 MHz reference
generator assembly to generate a 10
MHz reference signal. This signal is then
divided into five equivalent signals and
then amplified and delivered to the
output of the tray.
2.1.3 DM8-R Digital Modulator Tray
The DM8-R modulator Tray is an ATSC
compliant 8 VSB modulator that mounts
in a standard 19” rack. The DM8-R
modulator accepts a SMPTE-310 MPEG
data stream and outputs a 6 MHz wide
IF output centered at 44 MHz with a
pilot carrier at 46.69 MHz. The DM8-R
modulator provides linear and nonlinear
correction capability for the transmission
path as well as internal test sources that
are used during initial transmitter
installation. All of the functions of the
DM8-R modulator are controlled from
the LX Controller LCD display and
pushbuttons.
2.1.4 Amplifier Array Assemblies
The amplifier array assemblies each
contain (A9-A1) an 8-way splitter
(ZFSC-8-43) with four to six connections
used depending on the power level of
the transmitter, four to six (A1, A2, A3,