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The longwave Radio broadcasting band is the range of frequencies lying between 148.5 and 283.5 KHz (corresponding to Wavelength s between 1000 and 2000 Metre s). This range is included within the Low-frequency (LF) band, although the LF band covers a wider range than that used for longwave transmissions. BAND PROPAGATION CHARACTERISTICS Longwave signals have the property of following the curvature of the earth, making them ideal for continuous, continental Communication s. Unlike Shortwave radio, longwave signals do not Reflect or Refract using the Ionosphere , so there are fewer and less severe Interference -caused Fadeouts . Instead, the D-layer of the ionosphere and the surface of the earth serve as a Waveguide directing the signal . HISTORICAL SIGNIFICANCE Essentially all radio Transmitter s before 1924 were longwave transmitters . Propagation of Shorter Wavelengths was not understood until the Shortwave experiments by Amateur Radio operators in 1923 and by Marconi in 1924. Spark-gap Transmitter s were used prior to World War I , until the development of powerful Radio Alternators by General Electric just prior to the war. Vacuum tubes began to be used to generate radio frequencies in the mid-1920s. After 1924, use of longwave radio for long distance communication began to decline, as much less expensive shortwave transmitters began to carry increasingly heavy volumes of long distance communication. A period of explosive growth of shortwave communications began in 1927, leading to rapid decline in longwave radio usage. BROADCASTING In Europe , North Africa , Russia and Mongolia (ITU Region 1), longwave radio frequencies in the band 148.5 to 283.5 kHz are used for domestic and International Broadcasting . Carrier frequencies are multiples of 9 kHz ranging from 153 to 279 kHz. There are two exceptions in Germany, where two stations are offset by 3 kHz either side of 180 kHz. Historically LW stations operated on frequencies as high as 413 KHz (although the highest carrier frequency currently in use for LW broadcasting is 279 KHz) several countries transmitted radio programming over power lines or telephone lines using LW frequencies. These systems were known variously as Linjesender , Telefonrundspruch or Wire Broadcasting however these systems were phased out with the introduction of ISDN and later ADSL and it is believed that there are no longer any in operation . Some stations derive their carrier frequencies from an Atomic Clock . It can be therefore used as Frequency Standard . ITU Region 2 note In The Americas (ITU Region 2), there is no longwave broadcast band. In North America during the 1970s the longwave frequencies 167, 179 and 191 KHz were used for a short-lived network of Civil Defence Emergency Broadcasting stations with stations at Ault, Colorado and Cambridge, Kansas . Nowadays the 160-190 kHz range is used there for Part 15 Lowfers . The 190-435 kHz and 510-530 kHz bands are used for Navigational Beacons , and 500 kHz is the maritime distress (emergency) frequency. LIST OF LONGWAVE BROADCASTING TRANSMITTERS List of the most important longwave broadcasting transmitters (Source: http://de.wikipedia.org/wiki/Langwelle ). SEE ALSO
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