## The effect of filtering on the PSK waveform

While an unfiltered PSK signal has a constant envelope, the introduction of filtering to constrain the modulation bandwidth reintroduces an envelope variation to the PSK signal. The degree of envelope modulation introduced is a function of the severity of the pulse shaping employed. Shown here are examples of PSK waveforms for various values of root raised cosine filter roll-off. As expected, the smaller the value of a, the sharper the filter and the higher the peaks of the PSK signal. (The root raised cosine filter is used here, as it is the peak power rating of the transmitter that is usually of most concern to designers.) Further information on the peak to mean power ratios for M-ary PSK and QAM signals can be found in Chapter 6. |