Instruction Manual
6X Series Liquid-Cooled Transmitter Chapter 2, System Description
Instruction Manual, Rev. 0 2-2
compensate for errors in the SMPTE-310M input sample rate, ensuring the best
possible signal generation.
Non-volatile operation is achieved through flash-RAM (random access memory),
which instantaneously stores all digital settings for the entire exciter-modulator
system. This ensures that in case of power loss, the system will return to the
previously selected settings when power is restored, saving time by eliminating the
need to re-enter operating parameters.
Standard with all Axciters, Axcera Adaptive Correction Technology (AXACT™)
provides dynamic digital pre-correction that automatically tracks and corrects for
distortions, both linear and non-linear, in the complete transmitter system. All
adaptive operations are performed in the high-speed processor, which is capable of
equalizing a complete transmitter system in just sixty seconds, and completing a full
system optimization in about two minutes.
To obtain the necessary data, AXACT continuously samples the transmitter system
output, both before and after the mask filter, this is done through a down converter
located in the upconverter/driver tray. The modulator processes the data and the
necessary digital pre-correction is applied to the modulator output signal, resulting in
consistent transmitter system performance, independent of environmental changes.
The Axciter also performs over fifteen safety tests upon each adaptive correction run
to confirm that the new correction values are appropriate before applying them to
the on-air signal. This ensures that the signal will not be negatively affected by a
failure of an RF component in the sample path, such as an RF coupler, connector,
relay or cable.
DTVision Digital Signal Analysis and Test System is available as an option to the
Axciter. This system samples the transmitter output and measures critical
transmitter performance parameters. The information is then displayed in high-
resolution graphical format on the modulator's front panel display. Available
performance parameters include, digital SNR, error vector magnitude (EVM), eye
diagram, graphs of adaptive equalizer performance and RF spectrum, constellation
diagram, and more.
The Axciter employs dual processors to ensure on-air reliability. The low-level
control computer is a simple, highly reliable processor that is dedicated to running
the modulator hardware, thereby generating the ATSC signal. This processor uses a
highly reliable real-time operating system based on uC/OS for the mission critical
8VSB signal generation.
A second computer is dedicated to providing the adaptive processing, user interface,
diagnostics and graphics, using the very stable and reliable Linux operating system.
This high performance computer handles the processor intensive functions of
performing all adaptive correction and processing the data for the optional DTVision
signal analysis measurement and display, all without negatively affecting the critical
on-air signal path. In the unlikely event of a failure of this computer, the Axciter
remains on the air with a fully corrected ATSC signal. The Linux computer may even
be rebooted with no interruption of the on-air signal, and the Axciter is capable of a
cold start without the Linux computer.