The appearance of the waterfall display in a spectrum analyzer can vary depending on the modulation type of the signal being analyzed. Here are some common modulation types and their corresponding waterfall characteristics:
Amplitude Modulation (AM): In AM, the amplitude of the carrier wave is modulated by the audio or baseband signal. The waterfall display for an AM signal typically appears as a set of vertical lines or streaks. Each line represents a specific frequency component of the modulated signal, and its intensity or color represents the signal's power at that frequency over time. As the audio or baseband signal changes, the lines in the waterfall display will move or shift accordingly.
Frequency Modulation (FM): FM involves modulating the frequency of the carrier wave based on the audio or baseband signal. In a waterfall display, an FM signal will typically appear as horizontal lines or contours that extend across the frequency axis. The shape and intensity of these contours represent the frequency variations introduced by the modulation. The contour lines can change position and shape as the modulation signal changes.
Phase Modulation (PM): PM involves modulating the phase of the carrier wave according to the audio or baseband signal. In a waterfall display, a PM signal will exhibit characteristics similar to an FM signal. It will appear as horizontal lines or contours that represent the phase variations introduced by the modulation. The position and shape of these contours will change as the modulation signal varies.
Quadrature Amplitude Modulation (QAM): QAM is a digital modulation scheme that combines both amplitude and phase modulation. The waterfall display for a QAM signal will typically show a complex pattern of lines or contours. These patterns arise from the various combinations of amplitude and phase modulation used in QAM. The specific appearance of the waterfall display will depend on the constellation diagram used for the QAM modulation scheme.
Single Sideband (SSB): SSB modulation suppresses one of the sidebands and the carrier, resulting in a more efficient use of bandwidth. The waterfall display for an SSB signal will show a single set of vertical lines or streaks, representing the modulated signal's frequency components. However, one sideband and the carrier will be significantly attenuated or absent in the display, reflecting the suppression introduced by SSB modulation.
It's important to note that the actual appearance of the waterfall display can be influenced by various factors, including the specific settings and parameters of the spectrum analyzer, the resolution bandwidth, and the time span displayed. The examples mentioned above provide a general overview of how different modulation types may be represented in a waterfall display, but the exact visual characteristics can vary depending on the specific implementation and analysis settings.