  Depending on the application people use time-domain or frequency-domain
signals in order to measure or describe processes. First we will look at the
definition of these terms, produce some mathematical background and then apply
the tools to measurements made in the accelerator domain. We will first look at
signals produced by a single bunch passing once through a detector (transfer
line, linac), then periodic single bunch passages (circular accelerator) and at
the end multi-bunch passages in a circular accelerator.
