Instruction Manual

6X Series Liquid-Cooled Transmitter Chapter 2, System Description
Instruction Manual, Rev. 0 2-3
All ATSC Axciters are field upgradeable to new operating modes, such as ATSC M/H
Mobile DTV, DTx slave, Watermark, or other yet to be adopted ATSC enhancements.
A dual exciter system is an option for the 6X transmitter.
2.2: Exciter, Upconverter, Driver Tray
The exciter, upconverter, driver tray accepts the digital IF from the Axciter
modulator tray and converts it to any UHF channel using a very low phase noise
dual-conversion synthesized oscillator that is fully compliant with ATSC
recommendations. The output channel is easily selected through the front panel of
the system controller for a truly frequency agile exciter/driver chassis.
The Exciter, Upconverter, Driver Tray (1312871) contains a Frequency Agile
Upconverter Board (1309695), an Exciter Controller Board (1312413), a
Downconverter Board (1311103), Pre-Driver Exciter Assembly, 6X (1313190), and a
Button Board (1311306).
The 44 MHz digital IF input to the exciter, upconverter, driver tray connects through
the IF input jack located on the rear panel to the Frequency Agile Upconverter board.
The IF is converted to a second IF of 1044 MHz by an image rejection mixer mounted
on the Frequency Agile Upconverter board. A filter selects the appropriate
conversion product, which is then amplified to a level of approximately –8 dBm. The
1 GHz local oscillator (LO) frequency is generated on the board and is applied to a
high pass and low pass filter designed to eliminate any other interfering signals that
might be coupled into the 1 GHz LO. The LO is connected to an ALC circuit that
maintains the LO level to each mixer of +13 dBm over a wide range of 1 GHz LO
input levels. The LO sample is also sent to the Downconverter board.
This second IF signal is then applied to a second mixer mounted on the Frequency
Agile Upconverter board that downconverts it to a broadcast channel (2-69) by a LO
that operates in 1.0 MHz steps between 1.1-1.9 GHz depending on the channel
selected. The LO frequency equals the Channel center frequency plus 1044 MHz.
(As an example CH: 14: Center Frequency is 473.00 MHz therefore the LO2 is 473 +
1044, which equals 1517.00 MHz.)
The output of the mixer is connected to a 900 MHz Low pass filter to remove
unwanted conversion products. The resulting signal is amplified and wired to a Pin
Diode Attenuator which adjusts the gain of the tray that is controlled by an
Automatic Gain Control circuit, which maintains a constant power out of the
upconverter, and also the transmitter. The gain controlled output of the pin diode
circuit is connected to the output of the Tray.