Shortwave, medium wave, and longwave refer to different frequency bands used for radio broadcasting, while AM (Amplitude Modulation) is a modulation technique used to transmit signals within these frequency bands. Here's a breakdown of these terms:
AM (Amplitude Modulation): AM is a modulation technique where the amplitude of a carrier wave is varied in proportion to the audio signal being transmitted. It is one of the oldest methods of radio broadcasting. AM signals are typically transmitted in the frequency range from several hundred kilohertz (kHz) to a few megahertz (MHz). The audio information is encoded in the variations of the carrier wave's amplitude. AM radio stations are commonly found in the medium wave band.
Medium Wave (MW): Medium wave refers to the frequency band from around 540 kHz to 1600 kHz. AM broadcasting is predominantly done in this band. Medium wave signals can propagate over long distances by utilizing ground wave propagation during the day and skywave propagation at night. They are often used for local and regional broadcasting.
Longwave (LW): Longwave refers to the frequency band below the medium wave band, typically ranging from 30 kHz to 300 kHz. Longwave broadcasting has limited bandwidth and is primarily used for a few specific purposes such as time signal broadcasts and maritime navigation beacons. Longwave signals can propagate over very long distances due to their low frequency, but they require large antennas for efficient reception.
Shortwave (SW): Shortwave refers to the frequency band from around 1.6 MHz to 30 MHz. It is called "shortwave" because the wavelengths in this range are shorter compared to the longer wavelengths used in longwave and medium wave bands. Shortwave broadcasting is used for international broadcasting, reaching long distances by utilizing skywave propagation. Shortwave signals can bounce off the Earth's ionosphere, allowing them to travel across continents or even around the world.
In summary, the main difference lies in the frequency ranges and the propagation characteristics of these bands. AM is the modulation technique used for transmitting audio signals within the shortwave, medium wave, and longwave bands, with AM broadcasting primarily found in the medium wave band. Shortwave is used for long-distance international broadcasting, while longwave has limited bandwidth and is used for specific purposes like time signals and navigation beacons.