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2. Amateur radio frequency allocations - Wikipedia

   en.wikipedia.org/wiki/Amateur_radio_frequency...

   Radio amateurs use a variety of transmission modes, including Morse code, radioteletype, data, and voice. Specific frequency allocations vary from country to country and between ITU regions as specified in the current ITU HF frequency allocations for amateur radio. [1]

3. Shortwave bands - Wikipedia

   en.wikipedia.org/wiki/Shortwave_bands

   Shortwave bands are frequency allocations for use within the shortwave radio spectrum (the upper medium frequency [MF] band and all of the high frequency [HF] band). Radio waves in these frequency ranges can be used for very long distance (transcontinental) communication because they can reflect off layers of charged particles in the ionosphere and return to Earth beyond the horizon, a ...

4. Electromagnetic spectrum - Wikipedia

   en.wikipedia.org/wiki/Electromagnetic_spectrum

   Frequencies observed in astronomy range from 2.4 × 10 23 Hz (1 GeV gamma rays) down to the local plasma frequency of the ionized interstellar medium (~1 kHz). Wavelength is inversely proportional to the wave frequency, [ 1 ] so gamma rays have very short wavelengths that are fractions of the size of atoms , whereas wavelengths on the opposite ...

5. Frequency allocation - Wikipedia

   en.wikipedia.org/wiki/Frequency_allocation

   US frequency allocations chart, 2016. Frequency allocation (or spectrum allocation) is the part of spectrum management dealing with the designation and regulation of the electromagnetic spectrum into frequency bands, normally done by governments in most countries. [1]

6. Two-way radio - Wikipedia

   en.wikipedia.org/wiki/Two-way_radio

   This requires either two separate radio channels or channel sharing methods such as time-division duplex (TDD) to carry the two directions of the conversation simultaneously on a single radio frequency. [2] The first two-way radio was an AM-only device introduced by the Galvin Manufacturing Corporation in 1940 for use by the police and military ...

7. Radio spectrum - Wikipedia

   en.wikipedia.org/wiki/Radio_spectrum

   The radio spectrum is the part of the electromagnetic spectrum with frequencies from 3 Hz to 3,000 GHz (3 THz).Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particularly in telecommunication.