Radio waves are a form of electromagnetic radiation - like visible light waves only with much longer wavelengths. Visible light waves are oscillating electromagnetic signals with wavelengths of less than one millionth of a meter, whereas radio waves have wavelengths in the range of a few millimeters to several meters. Radio telescopes are designed to gather and concentrate radio waves from astronomical sources. The signals received are then electronically processed so they can be measured by a computer. Reception, amplification and filtering of these signals is the job of the receiver.