Medium wave

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Medium wave (MW) is the part of the medium frequency (MF) radio band used mainly for AM broadcasting. For Europe the MW band ranges from 526.5 kHz to 1606.5 kHz[1] and in North America an extended MW broadcast band goes from 535 kHz to 1705 kHz.[2]

Contents

Medium wave propagation characteristics

Medium wave signals have the property of following the curvature of the earth (the groundwave) at all times, and also refracting off the ionosphere at night (skywave). This makes this frequency band ideal for both local and continent-wide service, depending on the time of day. For example, during the day a radio receiver in the state of Maryland is able to receive reliable but weak signals from high-power stations WFAN/660 kHz, and WOR/710 kHz, 250 miles (400 km) away in New York City, due to groundwave propagation. The effectiveness of groundwave signals largely depends on ground conductivity—higher conductivity results in better propagation. At night, the same receiver may pick up signals as far away as Mexico City and Seattle reliably, depending on atmospheric noise and man-made interference.

Some experiments and trials are planned or under way for a digital modulation such as Digital Radio Mondiale (DRM)[3].

Medium wave in the Americas

Initially Broadcasting in the United states was restricted to two frequencies "Entertainment" was broadcast at "360 meters" (833 kHz), with stations required to switch to "485 meters" (619 kHz) when broadcasting weather forecasts, crop price reports and other government reports.[4] This arrangement had numerous practical difficulties. Early transmitters were technically crude and virtually impossible to set accurately on their intended frequency and if (as frequently happened) two (or more) stations in the same part of the country broadcast simultaneously the resultant interference meant that usually neither could be heard clearly. The Commerce Department rarely intervened in such cases but left it up to stations to enter into voluntary timesharing agreements amongst themselves. The addition of a third "entertainment" frequency (400 meters)[4] did little to solve this overcrowding.

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