An impulse train is a signal that contains an impulse in every cycle. The signal starts a new cycle every time there is a new spike. One sample per cycle has a non-zero amplitude. All other samples have an amplitude of zero.
This signal is periodic because it repeats the same cycle. The fundamental frequency of the signal is based on the period of time between each impulse. Spectrally, this signal has harmonics at both even and odd frequencies. All harmonics have the same amplitude.
Now that we have looked at several types of periodic signals, let’s move on to a different type of signal – white noise.