VSB (Digital Demod)

Select the VSB 8 or VSB 16 demodulation format to demodulate 8 VSB or 16 VSB (Vestigial Side Band) modulated signals.

The following topics provide additional information that is unique to VSB signals that will help successfully analyze VSB signals:

The VSB demodulator shifts the center frequency of the time data by Symbol Rate / 4 in order to align the constellation points in vertical lines. Without this shift, the constellation would be a set of concentric circles. This shift makes it easier to visually determine signal quality.

Prior to v11.20, traces containing demodulated data were displayed with the center frequency annotation matching the VSA center frequency. This has been changed in v11.20 to be consistent with the demodulated data. The center frequency annotation of the following traces is now set to be Symbol Rate / 4 below the VSA's center frequency. The data in these traces has not changed, only the center frequency annotation has changed.

The center frequency change will not be apparent in the time traces unless you view the frequency spectrum by using the Math functions to perform an FFT Fast Fourier Transform: A mathematical operation performed on a time-domain signal to yield the individual spectral components that constitute the signal. See Spectrum. on the time data.

In addition, the equalizer frequency response has been changed so that the filter generated is centered about the VSA center frequency. This allows the filter to be applied using the Fixed Equalization feature of the VSA. Previous to v11.20, the equalizer frequency response was shifted by Symbol Rate / 4 and therefore was not usable with the Fixed Equalization feature.