Tektronix RFA300A, User Manual

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Reference
3- 18
RFA300A Measurement Set 8VSB
A small DC offset is added to the baseband signal to produce a pilot at the carrier
frequency of the resulting modulated spectrum. The pilot is 0.3 dB of average
signal power and is used by the receiver for carrier acquisition. The receiver then
uses the Segment sync to lock on the symbol timing.
The 8VSB signal is transmitted as a single sideband suppressed carrier signal.
The baseband signal is typically mixed with a 44 MHz signal and passed through
a root-raised cosine filter. The output is a 44 MHz IF signal, upper sideband
only, with root-raised cosine response.
Closed-Loop Transmitter Control
This section provides a brief overview of the closed-loop feedback system that
can be used to control a transmitter exciter to maintain the signal within required
transmitting parameters.
A correction processor is either a closed-loop correction system or an open-loop
correction system, depending on how advanced the transmitter is. The correction
processor is used to shape the exciter signal to precorrect for frequency response
and envelope delay errors in the transmitter power amplifier. Precorrection can
also reduce non-linear errors.
A closed-loop system samples the outgoing RF to determine what type and how
much correction is needed and adjusts the precorrection accordingly. A less
advanced transmitter can have an open-loop precorrection system that requires
manual adjustments to the controls in a shaping network to produce the corrected
output.
Pilot Insertion
VSB Modulation
Correction Processor