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Live Stream Music Radio Free Internet Radio AM or FM modulation is mainly used, but digital systems such as DMR are being introduced. These systems have a fairly limited range, usually 3 to 20 miles (4.8 to 32 km) depending on terrain. Repeaters installed on tall buildings, hills, or mountain peaks are often used to increase the range when it is desired to cover a larger area than line-of-sight. A modulated radio wave, carrying an information signal, occupies a range of frequencies. The information in a radio signal is usually concentrated in narrow frequency bands called sidebands just above and below the carrier frequency. The width in hertz of the frequency range that the radio signal occupies, the highest frequency minus the lowest frequency, is called its bandwidth . Radiolocation is a generic term covering a variety of techniques that use radio waves to find the location of objects, or for navigation. Marine radar – an S or X band radar on ships used to detect nearby ships a