Shortwave Radio

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Shortwave radio operates between the frequencies of 2,310 kHz and 30 MHz (30,000 kHz) and came to be referred to as such in the early days of radio because the wavelengths associated with this frequency range were shorter than those commonly in use at that time. An alternate name is HF or high frequency radio. Short wavelengths are associated with high frequencies because there is an inverse relationship between frequency and wavelength.

Overview

High-frequency propagation

Shortwave frequencies are capable of reaching the other side of the planet because they can be refracted by the ionosphere (a phenomenon known as Skywave propagation). The selection of a frequency to use to reach a target area depends on several factors:

The distance from the transmitter to the target receiver.; Time of day. During the day, higher shortwave frequencies (> 12 MHz) can travel longer distances than lower ones; at night, this property is reversed.;

The dependence to the time of the day is due to a particular transient atmosphere ionized layer forming only during day when atoms are broken up into ions by sun photons. This layer is responsible for partial or total absorption of particular frequences.

Seasons, during the winter months the AM broadcast band tends to be more favorable because of longer hours of darkness.; Solar conditions, including the number of sunspots, solar flares, and overall solar activity. Solar flares can prevent the ionosphere from reflecting or refracting radio waves.; Type of modulation. Independent from the frequency, the receiver must be capable to receive the same modulation type of the transmitter. USB, LSB, AM, CW are all modes of modulation.;

Modulation formats used

Types of modulation frequently used in the shortwave frequency range are:

AM: amplitude modulation. Usually used for shortwave broadcasting, and some aeronautical communications.; NFM: Narrow-band frequency modulation. Because of the bandwidth required this is normally used for VHF communication, but some NFM transmissions occur in the higher HF frequencies.; SSB: Single sideband(USB/LSB): This is used for long-range communications by ships and aircraft, for voice transmissions by amateur radio operators, and for broadcasting. LSB is generally used below 10mhz and USB above 10mhz.; CW: Continuous/Carrier wave, which is used for Morse code communications.; DRM: Digital Radio Mondiale: digital modulation for use on bands below 30 MHz.; Various radioteletype, fax, digital, or other systems, which require software or special equipment to decode.;

Read more at Wikipedia.org