ATSC/8VSB Measurements - Digital Video and Audio Broadcasting Technology - page 449

• Shoulder attenuation

• Amplitude frequency response

• Pilot carrier amplitude

• Harmonics

Make the following settings on a modern spectrum analyzer:

• Center frequency at center of band
• Span 20 MHz

• RMS detector

• Resolution bandwidth 20 kHz

• Video bandwidth 200 kHz

• Slow sweep time (>1 s) to allow averaging by RMS detector

• No averaging function activated

Fig. 24.2. 8VSB signal spectrum with appropriate (left) and poor (right) vestigial
sideband suppression

Then the shoulder attenuation and, most importantly, the suppression of
the unwanted part of the lower sideband can be measured, as well as the
pilot amplitude and the amplitude distortion in the passband.

24.3 Constellation Analysis on 8VSB Signals

In contrast to a quadrature amplitude modulation (QAM) diagram, which
shows points, the constellation diagram of an 8VSB signal exhibits lines.
An ATSC test receiver usually comprises a constellation analyzer, which
displays the 8VSB diagram by 8 parallel vertical lines that should in the
ideal case be extremely narrow.