User's Manual

300-Watt Digital UHF Transmitter Chapter 2, System Description
DT830A, Rev. 1 2-2
The (A14-A1) 10-MHz reference
generator board (1519-1126) is located
in (A10) the 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, 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.
2.1.3 UHF Digital RF Output
Components
The RF output of the UHF exciter is fed to
an (A5) splitter and then to two UHF
amplifier trays that amplify the RF signal
to approximately 300 watts. A forward
power sample from the 4-way combiner
board inside each tray is connected to
the dual peak detector board that
provides a peak-detected forward sample
to the amplifier control board. This board
supplies the sample to the front panel
meter of the UHF amplifier tray.
Before exiting the UHF amplifier tray, the
RF is fed through a circulator to protect
the tray from high VSWR conditions. The
reject port of the circulator provides a
reject sample to the 4-way combiner
board that supplies the reflected sample
to the dual peak detector board. The
reflected sample connects to the
amplifier control board that provides the
sample to the front panel meter of the
tray. The output of (A6 and A7) the UHF
amplifier trays are combined in a tee and
then provide approximately 550 watts
average power. The output is connected
to a bandpass filter and then to the
output coupler assembly. There is a
coupler on the output of the bandpass
filter that provides –40 dB forward and
reflected samples to the system control
panel. The bandpass filter is tuned to
provide high out-of-band rejection of
unwanted products. The 7/8" coupler
assembly provides two forward power
samples and one reflected power sample.
The forward and reflected samples are
cabled to the visual/aural metering
boards in the UHF exciter. The forward
and reflected samples are processed to
provide detected power output samples
to the transmitter control board. The
transmitter control board connects the
forward and reflected power output
samples to the front panel meter for
monitoring.
2.1.5 Transmitter Power
Requirements
The transmitter needs an AC input of 220
VAC at 40 amps, or 80 amps for the
upgradeable version, connected to it in
order to operate. The 220 VAC input
connects to terminal block (TB1) in the
upper right rear of the cabinet and is part