In an analogue television signal (or a digital one for that matter) there are many voltages which will occur statistically more often than others. For example in a PAL signal the blanking and sync tip voltage occurs for reasonable percentages of the line time. When converted into the frequency domain these frequently occurring voltages will translate into concentrations of energy at particular frequencies. Such energy concentrations are more likely to produce annoying visible or audible interference to other services than if the voltages were spread over a varying voltage range. Therefore a special "energy dispersal waveform" is added to spread any possible concentration of energy at specific frequencies.
The analogue energy dispersal waveform is usually a triangular waveform that is frame aligned with the transmitted signal.
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