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107-786: Transmitting on shortwave , Radio Rebelde also broadcast the latest combat news, music and spoken literature to the people of Cuba during the Cuban Revolution . Today, Radio Rebelde has forty-four transmitters on the FM dial covering 98 percent of the island of Cuba, plus a shortwave signal on the 60-meter band at 5.025 MHz, (5025 kHz) and several AM transmitters on various frequencies, most commonly 530, 540, 550, 560, 600, 610, 620, 670, 710, 770, 1180, and 1620 kHz, and on FM 96.7 MHz in Havana. The radio broadcasts were initiated in February 1958 by

214-410: A rock music context. In 1975, German electronic music band Kraftwerk recorded a full length concept album around simulated radiowave and shortwave sounds, entitled Radio-Activity . The The 's Radio Cineola monthly broadcasts drew heavily on shortwave radio sound. The development of direct broadcasts from satellites has reduced the demand for shortwave receiver hardware, but there are still

321-666: A spark-gap transmitter to produce a signal with a frequency of approximately 500  kHz and a power of 100 times more than any radio signal previously produced. The message received was three dits, the Morse code for the letter S . To reach Newfoundland the signal would have to bounce off the ionosphere twice. Dr. Jack Belrose has contested this, however, based on theoretical and experimental work. However, Marconi did achieve transatlantic wireless communications in Glace Bay, Nova Scotia , one year later. In 1902, Oliver Heaviside proposed

428-411: A bit to absorption on frequencies above. However, during intense sporadic E events, the E s layer can reflect frequencies up to 50 MHz and higher. The vertical structure of the E layer is primarily determined by the competing effects of ionization and recombination. At night the E layer weakens because the primary source of ionization is no longer present. After sunset an increase in the height of

535-689: A geomagnetic storm the F₂ layer will become unstable, fragment, and may even disappear completely. In the Northern and Southern polar regions of the Earth aurorae will be observable in the night sky. Lightning can cause ionospheric perturbations in the D-region in one of two ways. The first is through VLF (very low frequency) radio waves launched into the magnetosphere . These so-called "whistler" mode waves can interact with radiation belt particles and cause them to precipitate onto

642-403: A great number of shortwave broadcasters. A new digital radio technology, Digital Radio Mondiale (DRM), is expected to improve the quality of shortwave audio from very poor to adequate. The future of shortwave radio is threatened by the rise of power line communication (PLC), also known as Broadband over Power Lines (BPL), which uses a data stream transmitted over unshielded power lines. As

749-483: A high frequency (3–30 MHz) radio blackout that can persist for many hours after strong flares. During this time very low frequency (3–30 kHz) signals will be reflected by the D layer instead of the E layer, where the increased atmospheric density will usually increase the absorption of the wave and thus dampen it. As soon as the X-rays end, the sudden ionospheric disturbance (SID) or radio black-out steadily declines as

856-421: A large-scale study into the transmission characteristics of short-wavelength waves and to determine their suitability for long-distance transmissions. Franklin rigged up a large antenna at Poldhu Wireless Station , Cornwall , running on 25 kW of power. In June and July 1923, wireless transmissions were completed during nights on 97 meters (about 3 MHz) from Poldhu to Marconi's yacht Elettra in

963-417: A radio wave reaches the ionosphere, the electric field in the wave forces the electrons in the ionosphere into oscillation at the same frequency as the radio wave. Some of the radio-frequency energy is given up to this resonant oscillation. The oscillating electrons will then either be lost to recombination or will re-radiate the original wave energy. Total refraction can occur when the collision frequency of

1070-479: A result of lightning activity. Their subsequent research has focused on the mechanism by which this process can occur. Due to the ability of ionized atmospheric gases to refract high frequency (HF, or shortwave ) radio waves, the ionosphere can reflect radio waves directed into the sky back toward the Earth. Radio waves directed at an angle into the sky can return to Earth beyond the horizon. This technique, called "skip" or " skywave " propagation, has been used since

1177-417: A result of the multi-layer structure of the ionosphere , propagation often simultaneously occurs on different paths, scattered by the ‘E’ or ‘F’ layer and with different numbers of hops, a phenomenon that may be disturbed for certain techniques. Particularly for lower frequencies of the shortwave band, absorption of radio frequency energy in the lowest ionospheric layer, the ‘D’ layer , may impose

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1284-436: A serious limit. This is due to collisions of electrons with neutral molecules, absorbing some of a radio frequency 's energy and converting it to heat. Predictions of skywave propagation depend on: Several different types of modulation are used to incorporate information in a short-wave signal. Amplitude modulation is the simplest type and the most commonly used for shortwave broadcasting . The instantaneous amplitude of

1391-531: A shortwave carrier. These generally require special equipment to decode, such as software on a computer equipped with a sound card. Note that on modern computer-driven systems, digital modes are typically sent by coupling a computer's sound output to the SSB input of a radio. Some established users of the shortwave radio bands may include: Sporadic or non-traditional users of the shortwave bands may include: The World Radiocommunication Conference (WRC), organized under

1498-405: A single transmitter, making it difficult for government authorities to censor them. Shortwave radio is also often used by aircraft. The name "shortwave" originated during the beginning of radio in the early 20th century, when the radio spectrum was divided into long wave (LW), medium wave (MW), and short wave (SW) bands based on the length of the wave. Shortwave radio received its name because

1605-532: A very limited spectrum available for long-distance communication, and the very expensive transmitters , receivers and gigantic antennas. Long waves are also difficult to beam directionally, resulting in a major loss of power over long distances. Prior to the 1920s, the shortwave frequencies above 1.5 MHz were regarded as useless for long-distance communication and were designated in many countries for amateur use. Guglielmo Marconi , pioneer of radio, commissioned his assistant Charles Samuel Franklin to carry out

1712-404: Is actually lower in the local summer months. This effect is known as the winter anomaly. The anomaly is always present in the northern hemisphere, but is usually absent in the southern hemisphere during periods of low solar activity. Within approximately ± 20 degrees of the magnetic equator , is the equatorial anomaly. It is the occurrence of a trough in the ionization in the F 2 layer at

1819-460: Is also common, sometimes to distances of 15,000 km (9,300 mi) or more. The F layer or region, also known as the Appleton–Barnett layer, extends from about 150 km (93 mi) to more than 500 km (310 mi) above the surface of Earth. It is the layer with the highest electron density, which implies signals penetrating this layer will escape into space. Electron production

1926-652: Is currently used to compensate for ionospheric effects in GPS . This model was developed at the US Air Force Geophysical Research Laboratory circa 1974 by John (Jack) Klobuchar . The Galileo navigation system uses the NeQuick model . GALILEO broadcasts 3 coefficients to compute the effective ionization level, which is then used by the NeQuick model to compute a range delay along the line-of-sight. The open system electrodynamic tether , which uses

2033-400: Is customarily used below 10 MHz and USB (upper sideband) above 10 MHz, non-amateur services use USB regardless of frequency. Vestigial sideband transmits the carrier and one complete sideband, but filters out most of the other sideband. It is a compromise between AM and SSB, enabling simple receivers to be used, but requires almost as much transmitter power as AM. Its main advantage

2140-448: Is dominated by extreme ultraviolet (UV, 10–100 nm) radiation ionizing atomic oxygen. The F layer consists of one layer (F 2 ) at night, but during the day, a secondary peak (labelled F 1 ) often forms in the electron density profile. Because the F 2 layer remains by day and night, it is responsible for most skywave propagation of radio waves and long distance high frequency (HF, or shortwave ) radio communications. Above

2247-455: Is eliminated as well as the residual carrier, only the remaining set is transmitted. This reduces power in the transmission, as roughly 2 ⁄ 3 of the energy sent by an AM signal is in the carrier, which is not needed to recover the information contained in the signal. It also reduces signal bandwidth , enabling less than one-half the AM signal bandwidth to be used. The drawback is the receiver

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2354-508: Is enough to absorb most (if not all) transpolar HF radio signal transmissions. Such events typically last less than 24 to 48 hours. The E layer is the middle layer, 90 to 150 km (56 to 93 mi) above the surface of the Earth. Ionization is due to soft X-ray (1–10 nm) and far ultraviolet (UV) solar radiation ionization of molecular oxygen (O 2 ). Normally, at oblique incidence, this layer can only reflect radio waves having frequencies lower than about 10 MHz and may contribute

2461-476: Is for transmitting audio, like the analog modes above. Continuous wave (CW) is on-and-off keying of a sine-wave carrier, used for Morse code communications and Hellschreiber facsimile -based teleprinter transmissions. It is a data mode, although often listed separately. It is typically received via lower or upper SSB modes. Radioteletype , fax, digital, slow-scan television , and other systems use forms of frequency-shift keying or audio subcarriers on

2568-534: Is higher than the plasma frequency of the ionosphere, then the electrons cannot respond fast enough, and they are not able to re-radiate the signal. It is calculated as shown below: where N = electron density per m and f critical is in Hz. The Maximum Usable Frequency (MUF) is defined as the upper frequency limit that can be used for transmission between two points at a specified time. where α {\displaystyle \alpha } = angle of arrival ,

2675-417: Is more complicated, since it must re-create the carrier to recover the signal. Small errors in the detection process greatly affect the pitch of the received signal. As a result, single sideband is not used for music or general broadcast. Single sideband is used for long-range voice communications by ships and aircraft, citizen's band , and amateur radio operators. In amateur radio operation lower sideband (LSB)

2782-411: Is sufficient to affect radio propagation . This portion of the atmosphere is partially ionized and contains a plasma which is referred to as the ionosphere. Ultraviolet (UV), X-ray and shorter wavelengths of solar radiation are ionizing, since photons at these frequencies contain sufficient energy to dislodge an electron from a neutral gas atom or molecule upon absorption. In this process

2889-537: Is that only half the bandwidth of an AM signal is used. It is used by the Canadian standard time signal station CHU . Vestigial sideband was used for analog television and by ATSC , the digital TV system used in North America. Narrow-band frequency modulation (NBFM or NFM) is used typically above 20 MHz. Because of the larger bandwidth required, NBFM is commonly used for VHF communication. Regulations limit

2996-591: Is the ionized part of the upper atmosphere of Earth , from about 48 km (30 mi) to 965 km (600 mi) above sea level , a region that includes the thermosphere and parts of the mesosphere and exosphere . The ionosphere is ionized by solar radiation . It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere . It has practical importance because, among other functions, it influences radio propagation to distant places on Earth . It also affects GPS signals that travel through this layer. As early as 1839,

3103-405: Is the main reason for absorption of HF radio waves , particularly at 10 MHz and below, with progressively less absorption at higher frequencies. This effect peaks around noon and is reduced at night due to a decrease in the D layer's thickness; only a small part remains due to cosmic rays . A common example of the D layer in action is the disappearance of distant AM broadcast band stations in

3210-502: Is useful in crossing international boundaries and covering large areas at low cost. Automated services still use shortwave radio frequencies, as do radio amateur hobbyists for private recreational contacts and to assist with emergency communications during natural disasters. Armed forces use shortwave so as to be independent of vulnerable infrastructure, including satellites, and the low latency of shortwave communications make it attractive to stock traders, where milliseconds count. When

3317-587: The ALLISS antenna technology) to concentrate radio energy at the target area. Shortwave possesses a number of advantages over newer technologies: Shortwave radio's benefits are sometimes regarded as being outweighed by its drawbacks, including: The Asia-Pacific Telecommunity estimates that there are approximately 600 million shortwave broadcast-radio receivers in use in 2002. WWCR claims that there are 1.5 billion shortwave receivers worldwide. Many hobbyists listen to shortwave broadcasters. In some cases,

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3424-506: The Cape Verde Islands . In September 1924, Marconi arranged for transmissions to be made day and night on 32 meters (about 9.4 MHz) from Poldhu to his yacht in the harbour at Beirut , to which he had sailed, and was "astonished" to find he could receive signals "throughout the day". Franklin went on to refine the directional transmission by inventing the curtain array aerial system. In July 1924, Marconi entered into contracts with

3531-583: The Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI). The major data sources are the worldwide network of ionosondes , the powerful incoherent scatter radars (Jicamarca, Arecibo , Millstone Hill, Malvern, St Santin), the ISIS and Alouette topside sounders , and in situ instruments on several satellites and rockets. IRI is updated yearly. IRI is more accurate in describing

3638-700: The medium frequency band (MF) , to the bottom of the VHF band . Radio waves in the shortwave band can be reflected or refracted from a layer of electrically charged atoms in the atmosphere called the Ionosphere . Therefore, short waves directed at an angle into the sky can be reflected back to Earth at great distances, beyond the horizon. This is called skywave or "skip" propagation . Thus shortwave radio can be used for communication over very long distances, in contrast to radio waves of higher frequency, which travel in straight lines ( line-of-sight propagation ) and are limited by

3745-448: The troposphere , extends from the surface to about 10 km (6 mi). Above that is the stratosphere , followed by the mesosphere. In the stratosphere incoming solar radiation creates the ozone layer . At heights of above 80 km (50 mi), in the thermosphere , the atmosphere is so thin that free electrons can exist for short periods of time before they are captured by a nearby positive ion . The number of these free electrons

3852-399: The 1920s to communicate at international or intercontinental distances. The returning radio waves can reflect off the Earth's surface into the sky again, allowing greater ranges to be achieved with multiple hops . This communication method is variable and unreliable, with reception over a given path depending on time of day or night, the seasons, weather, and the 11-year sunspot cycle . During

3959-416: The 1920s. By 1928, more than half of long-distance communications had moved from transoceanic cables and longwave wireless services to shortwave, and the overall volume of transoceanic shortwave communications had vastly increased. Shortwave stations had cost and efficiency advantages over massive longwave wireless installations. However, some commercial longwave communications stations remained in use until

4066-421: The 1960s. Long-distance radio circuits also reduced the need for new cables, although the cables maintained their advantages of high security and a much more reliable and better-quality signal than shortwave. The cable companies began to lose large sums of money in 1927. A serious financial crisis threatened viability of cable companies that were vital to strategic British interests. The British government convened

4173-522: The BPL frequencies used overlap with shortwave bands, severe distortions can make listening to analog shortwave radio signals near power lines difficult or impossible. According to Andy Sennitt, former editor of the World Radio TV Handbook , shortwave is a legacy technology, which is expensive and environmentally unfriendly. A few countries are hanging on to it, but most have faced up to the fact that

4280-522: The Beethoven Bicentennial in Opus ;1970 with filtered and distorted snippets of Beethoven pieces – Spiral (1968), Pole , Expo (both 1969–1970), and Michaelion (1997). Cypriot composer Yannis Kyriakides incorporated shortwave numbers station transmissions in his 1999 ConSPIracy cantata . Holger Czukay , a student of Stockhausen, was one of the first to use shortwave in

4387-641: The British General Post Office (GPO) to install high-speed shortwave telegraphy circuits from London to Australia, India, South Africa and Canada as the main element of the Imperial Wireless Chain . The UK-to-Canada shortwave "Beam Wireless Service" went into commercial operation on 25 October 1926. Beam Wireless Services from the UK to Australia, South Africa and India went into service in 1927. Shortwave communications began to grow rapidly in

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4494-443: The D layer, so there are many more neutral air molecules than ions. Medium frequency (MF) and lower high frequency (HF) radio waves are significantly attenuated within the D layer, as the passing radio waves cause electrons to move, which then collide with the neutral molecules, giving up their energy. Lower frequencies experience greater absorption because they move the electrons farther, leading to greater chance of collisions. This

4601-686: The E layer maximum increases the range to which radio waves can travel by reflection from the layer. This region is also known as the Kennelly–Heaviside layer or simply the Heaviside layer. Its existence was predicted in 1902 independently and almost simultaneously by the American electrical engineer Arthur Edwin Kennelly (1861–1939) and the British physicist Oliver Heaviside (1850–1925). In 1924 its existence

4708-532: The F 1 layer. The F 2 layer persists by day and night and is the main region responsible for the refraction and reflection of radio waves. The D layer is the innermost layer, 48 to 90 km (30 to 56 mi) above the surface of the Earth. Ionization here is due to Lyman series -alpha hydrogen radiation at a wavelength of 121.6 nanometre (nm) ionizing nitric oxide (NO). In addition, solar flares can generate hard X-rays (wavelength < 1 nm ) that ionize N 2 and O 2 . Recombination rates are high in

4815-455: The F 2 layer daytime ion production is higher in the summer, as expected, since the Sun shines more directly on the Earth. However, there are seasonal changes in the molecular-to-atomic ratio of the neutral atmosphere that cause the summer ion loss rate to be even higher. The result is that the increase in the summertime loss overwhelms the increase in summertime production, and total F 2 ionization

4922-484: The F layer, the number of oxygen ions decreases and lighter ions such as hydrogen and helium become dominant. This region above the F layer peak and below the plasmasphere is called the topside ionosphere. From 1972 to 1975 NASA launched the AEROS and AEROS B satellites to study the F region. An ionospheric model is a mathematical description of the ionosphere as a function of location, altitude, day of year, phase of

5029-667: The German mathematician and physicist Carl Friedrich Gauss postulated that an electrically conducting region of the atmosphere could account for observed variations of Earth's magnetic field. Sixty years later, Guglielmo Marconi received the first trans-Atlantic radio signal on December 12, 1901, in St. John's, Newfoundland (now in Canada ) using a 152.4 m (500 ft) kite-supported antenna for reception. The transmitting station in Poldhu , Cornwall, used

5136-575: The Imperial Wireless and Cable Conference in 1928 "to examine the situation that had arisen as a result of the competition of Beam Wireless with the Cable Services". It recommended and received government approval for all overseas cable and wireless resources of the Empire to be merged into one system controlled by a newly formed company in 1929, Imperial and International Communications Ltd. The name of

5243-601: The Internet, in that they listen only, and never attempt to send out their own signals. Other listeners participate in clubs, or actively send and receive QSL cards, or become involved with amateur radio and start transmitting on their own. Many listeners tune the shortwave bands for the programmes of stations broadcasting to a general audience (such as Radio Taiwan International , China Radio International , Voice of America , Radio France Internationale , BBC World Service , Voice of Korea , Radio Free Sarawak etc.). Today, through

5350-521: The Second National Radio Conference in 1923 – forced amateurs to shift to shorter and shorter wavelengths; however, amateurs were limited by regulation to wavelengths longer than 150 meters (2 MHz). A few fortunate amateurs who obtained special permission for experimental communications at wavelengths shorter than 150 meters completed hundreds of long-distance two-way contacts on 100 meters (3 MHz) in 1923 including

5457-450: The Sun at any one time. Sunspot active regions are the source of increased coronal heating and accompanying increases in EUV and X-ray irradiance, particularly during episodic magnetic eruptions that include solar flares that increase ionization on the sunlit side of the Earth and solar energetic particle events that can increase ionization in the polar regions. Thus the degree of ionization in

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5564-441: The angle of the wave relative to the horizon , and sin is the sine function. The cutoff frequency is the frequency below which a radio wave fails to penetrate a layer of the ionosphere at the incidence angle required for transmission between two specified points by refraction from the layer. There are a number of models used to understand the effects of the ionosphere on global navigation satellite systems. The Klobuchar model

5671-452: The assigned bands, there may be small differences between countries or regions. For example, in the official bandplan of the Netherlands , the 49 m band starts at 5.95 MHz, the 41 m band ends at 7.45 MHz, the 11 m band starts at 25.67 MHz, and the 120 m, 90 m, and 60 m bands are absent altogether. International broadcasters sometimes operate outside

5778-449: The atmosphere near the magnetic poles increasing the ionization of the D and E layers. PCA's typically last anywhere from about an hour to several days, with an average of around 24 to 36 hours. Coronal mass ejections can also release energetic protons that enhance D-region absorption in the polar regions. Geomagnetic storms and ionospheric storms are temporary and intense disturbances of the Earth's magnetosphere and ionosphere. During

5885-486: The auspices of the International Telecommunication Union , allocates bands for various services in conferences every few years. The last WRC took place in 2023. As of WRC-97 in 1997, these bands were allocated for international broadcasting . AM shortwave broadcasting channels are allocated with a 5 kHz separation for traditional analog audio broadcasting: Although countries generally follow

5992-451: The bandwidth of a signal transmitted in the HF bands, and the advantages of frequency modulation are greatest if the FM signal has a wide bandwidth. NBFM is limited to short-range transmissions due to the multiphasic distortions created by the ionosphere. Digital Radio Mondiale (DRM) is a digital modulation for use on bands below 30 MHz. It is a digital signal, like the data modes, below, but

6099-431: The carrier is controlled by the amplitude of the signal (speech, or music, for example). At the receiver, a simple detector recovers the desired modulation signal from the carrier. Single-sideband transmission is a form of amplitude modulation but in effect filters the result of modulation. An amplitude-modulated signal has frequency components both above and below the carrier frequency . If one set of these components

6206-567: The clandestine station and begin broadcasting. Early broadcast efforts were conducted by Luis Orlando Rodríguez, who later became Minister for the Interior. The first broadcast began with the announcement: "Aquí Radio Rebelde, the voice of the Sierra Maestra, transmitting for all Cuba on the 20-meter band at 5 and 9 pm daily... I'm station director Capt. Luis Orlando Rodríguez." Later, Carlos Franqui arrived from Miami , United States , to become

6313-586: The company was changed to Cable and Wireless Ltd. in 1934. A resurgence of long-distance cables began in 1956 with the laying of TAT-1 across the Atlantic Ocean, the first voice frequency cable on this route. This provided 36 high-quality telephone channels and was soon followed by even higher-capacity cables all around the world. Competition from these cables soon ended the economic viability of shortwave radio for commercial communication. Amateur radio operators also discovered that long-distance communication

6420-412: The daytime. During solar proton events , ionization can reach unusually high levels in the D-region over high and polar latitudes. Such very rare events are known as Polar Cap Absorption (or PCA) events, because the increased ionization significantly enhances the absorption of radio signals passing through the region. In fact, absorption levels can increase by many tens of dB during intense events, which

6527-534: The discovery of HF radio propagation via the ionosphere in 1923. In 1925, observations during a solar eclipse in New York by Dr. Alfred N. Goldsmith and his team demonstrated the influence of sunlight on radio wave propagation, revealing that short waves became weak or inaudible while long waves steadied during the eclipse, thus contributing to the understanding of the ionosphere's role in radio transmission. In 1926, Scottish physicist Robert Watson-Watt introduced

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6634-549: The distribution of radio programs, such as satellite radio and cable broadcasting as well as IP-based transmissions , shortwave broadcasting lost importance. Initiatives for the digitization of broadcasting did not bear fruit either, and so as of 2024 , few broadcasters continue to broadcast programs on shortwave. However, shortwave remains important in war zones, such as in the Russo-Ukrainian war , and shortwave broadcasts can be transmitted over thousands of miles from

6741-423: The electrons in the D-region recombine rapidly and propagation gradually returns to pre-flare conditions over minutes to hours depending on the solar flare strength and frequency. Associated with solar flares is a release of high-energy protons. These particles can hit the Earth within 15 minutes to 2 hours of the solar flare. The protons spiral around and down the magnetic field lines of the Earth and penetrate into

6848-431: The equator and crests at about 17 degrees in magnetic latitude. The Earth's magnetic field lines are horizontal at the magnetic equator. Solar heating and tidal oscillations in the lower ionosphere move plasma up and across the magnetic field lines. This sets up a sheet of electric current in the E region which, with the horizontal magnetic field, forces ionization up into the F layer, concentrating at ± 20 degrees from

6955-572: The evolution of the Internet, the hobbyist can listen to shortwave signals via remotely controlled or web controlled shortwave receivers around the world, even without owning a shortwave radio. Many international broadcasters offer live streaming audio on their websites and a number have closed their shortwave service entirely, or severely curtailed it, in favour of internet transmission. Shortwave listeners, or SWLs, can obtain QSL cards from broadcasters, utility stations or amateur radio operators as trophies of

7062-604: The existence of the Kennelly–Heaviside layer of the ionosphere which bears his name. Heaviside's proposal included means by which radio signals are transmitted around the Earth's curvature. Also in 1902, Arthur Edwin Kennelly discovered some of the ionosphere's radio-electrical properties. In 1912, the U.S. Congress imposed the Radio Act of 1912 on amateur radio operators , limiting their operations to frequencies above 1.5 MHz (wavelength 200 meters or smaller). The government thought those frequencies were useless. This led to

7169-415: The first half of the 20th century it was widely used for transoceanic telephone and telegraph service, and business and diplomatic communication. Due to its relative unreliability, shortwave radio communication has been mostly abandoned by the telecommunications industry, though it remains important for high-latitude communication where satellite-based radio communication is not possible. Shortwave broadcasting

7276-457: The first radio modification of the ionosphere; HAARP ran a series of experiments in 2017 using the eponymous Luxembourg Effect . Edward V. Appleton was awarded a Nobel Prize in 1947 for his confirmation in 1927 of the existence of the ionosphere. Lloyd Berkner first measured the height and density of the ionosphere. This permitted the first complete theory of short-wave radio propagation. Maurice V. Wilkes and J. A. Ratcliffe researched

7383-713: The first successful transatlantic tests in December ;1921, operating in the 200 meter mediumwave band (near 1,500 kHz, inside the modern AM broadcast band), which at that time was the shortest wavelength / highest frequency available to amateur radio. In 1922 hundreds of North American amateurs were heard in Europe on 200 meters and at least 20 North American amateurs heard amateur signals from Europe. The first two-way communications between North American and Hawaiian amateurs began in 1922 at 200 meters. Although operation on wavelengths shorter than 200 meters

7490-597: The first transatlantic two-way contacts. By 1924 many additional specially licensed amateurs were routinely making transoceanic contacts at distances of 6,000 miles (9,600 km) and more. On 21 September 1924 several amateurs in California completed two-way contacts with an amateur in New Zealand . On 19 October amateurs in New Zealand and England completed a 90 minute two-way contact nearly halfway around

7597-456: The glory days of shortwave have gone. Religious broadcasters will still use it because they are not too concerned with listening figures. However, Thomas Witherspoon, editor of shortwave news site SWLingPost.com wrote that shortwave remains the most accessible international communications medium that still provides listeners with the protection of complete anonymity. Ionosphere The ionosphere ( / aɪ ˈ ɒ n ə ˌ s f ɪər / )

7704-472: The goal is to hear as many stations from as many countries as possible ( DXing ) ; others listen to specialized shortwave utility, or "ute", transmissions such as maritime, naval, aviation, or military signals. Others focus on intelligence signals from numbers stations , stations which transmit strange broadcast usually for intelligence operations, or the two way communications by amateur radio operators. Some short wave listeners behave analogously to "lurkers" on

7811-492: The harmonics of natural sound and creating at times a strange "spacey" quality due to echoes and phase distortion. Evocations of shortwave reception distortions have been incorporated into rock and classical compositions, by means of delays or feedback loops, equalizers, or even playing shortwave radios as live instruments. Snippets of broadcasts have been mixed into electronic sound collages and live musical instruments, by means of analogue tape loops or digital samples . Sometimes

7918-573: The hobby. Some stations even give out special certificates, pennants, stickers and other tokens and promotional materials to shortwave listeners. Some musicians have been attracted to the unique aural characteristics of shortwave radio which – due to the nature of amplitude modulation, varying propagation conditions, and the presence of interference – generally has lower fidelity than local broadcasts (particularly via FM stations). Shortwave transmissions often have bursts of distortion, and "hollow" sounding loss of clarity at certain aural frequencies, altering

8025-494: The interactions of the ions and electrons with the neutral atmosphere and sunlight, or it may be a statistical description based on a large number of observations or a combination of physics and observations. One of the most widely used models is the International Reference Ionosphere (IRI), which is based on data and specifies the four parameters just mentioned. The IRI is an international project sponsored by

8132-465: The ionosphere and decrease the ionization. Sydney Chapman proposed that the region below the ionosphere be called neutrosphere (the neutral atmosphere ). At night the F layer is the only layer of significant ionization present, while the ionization in the E and D layers is extremely low. During the day, the D and E layers become much more heavily ionized, as does the F layer, which develops an additional, weaker region of ionisation known as

8239-421: The ionosphere follows both a diurnal (time of day) cycle and the 11-year solar cycle . There is also a seasonal dependence in ionization degree since the local winter hemisphere is tipped away from the Sun, thus there is less received solar radiation. Radiation received also varies with geographical location (polar, auroral zones, mid-latitudes , and equatorial regions). There are also mechanisms that disturb

8346-404: The ionosphere is less than the radio frequency, and if the electron density in the ionosphere is great enough. A qualitative understanding of how an electromagnetic wave propagates through the ionosphere can be obtained by recalling geometric optics . Since the ionosphere is a plasma, it can be shown that the refractive index is less than unity. Hence, the electromagnetic "ray" is bent away from

8453-444: The ionosphere, adding ionization to the D-region. These disturbances are called "lightning-induced electron precipitation " (LEP) events. Additional ionization can also occur from direct heating/ionization as a result of huge motions of charge in lightning strikes. These events are called early/fast. In 1925, C. T. R. Wilson proposed a mechanism by which electrical discharge from lightning storms could propagate upwards from clouds to

8560-474: The ionosphere. On July 26, 1963, the first operational geosynchronous satellite Syncom 2 was launched. On board radio beacons on this satellite (and its successors) enabled – for the first time – the measurement of total electron content (TEC) variation along a radio beam from geostationary orbit to an earth receiver. (The rotation of the plane of polarization directly measures TEC along the path.) Australian geophysicist Elizabeth Essex-Cohen from 1969 onwards

8667-646: The ionosphere. Around the same time, Robert Watson-Watt, working at the Radio Research Station in Slough, UK, suggested that the ionospheric sporadic E layer (E s ) appeared to be enhanced as a result of lightning but that more work was needed. In 2005, C. Davis and C. Johnson, working at the Rutherford Appleton Laboratory in Oxfordshire, UK, demonstrated that the E s layer was indeed enhanced as

8774-445: The ionosphere. At the magnetic dip equator, where the geomagnetic field is horizontal, this electric field results in an enhanced eastward current flow within ± 3 degrees of the magnetic equator, known as the equatorial electrojet . When the Sun is active, strong solar flares can occur that hit the sunlit side of Earth with hard X-rays. The X-rays penetrate to the D-region, releasing electrons that rapidly increase absorption, causing

8881-462: The light electron obtains a high velocity so that the temperature of the created electronic gas is much higher (of the order of thousand K) than the one of ions and neutrals. The reverse process to ionization is recombination , in which a free electron is "captured" by a positive ion. Recombination occurs spontaneously, and causes the emission of a photon carrying away the energy produced upon recombination. As gas density increases at lower altitudes,

8988-400: The magnetic equator. This phenomenon is known as the equatorial fountain . The worldwide solar-driven wind results in the so-called Sq (solar quiet) current system in the E region of the Earth's ionosphere ( ionospheric dynamo region ) (100–130 km (60–80 mi) altitude). Resulting from this current is an electrostatic field directed west–east (dawn–dusk) in the equatorial day side of

9095-590: The movement's overall director of information. Soon, as the fighting intensified, Franqui and the transmitter relocated to Fidel Castro 's command post in La Plata, Cuba . The broadcasts became a vital source of communication due to increased government restrictions on the Cuban press. A new boosted transmitter in La Plata carried lengthy interviews and speeches by Fidel Castro and provided radiotelephone communication between

9202-424: The normal rather than toward the normal as would be indicated when the refractive index is greater than unity. It can also be shown that the refractive index of a plasma, and hence the ionosphere, is frequency-dependent, see Dispersion (optics) . The critical frequency is the limiting frequency at or below which a radio wave is reflected by an ionospheric layer at vertical incidence . If the transmitted frequency

9309-809: The normal the WRC-allocated bands or use off-channel frequencies. This is done for practical reasons, or to attract attention in crowded bands (60 m, 49 m, 40 m, 41 m, 31 m, 25 m). The new digital audio broadcasting format for shortwave DRM operates 10 kHz or 20 kHz channels. There are some ongoing discussions with respect to specific band allocation for DRM, as it mainly transmitted in 10 kHz format. The power used by shortwave transmitters ranges from less than one watt for some experimental and amateur radio transmissions to 500 kilowatts and higher for intercontinental broadcasters and over-the-horizon radar . Shortwave transmitting centers often use specialized antenna designs (like

9416-520: The rebel army's media wing, under Guevara's supervision. Guevara had reportedly been impressed by the power of radio after experiencing first hand the role of a CIA clandestine radio station, La Voz de la Liberación , in ousting the government of Jacobo Arbenz in Guatemala . An electric generator and the first radio equipment had arrived in Pata de la Mesa, Guevara's command post, where the rebels were to set up

9523-438: The rebel columns throughout the region. Expansions in rebel numbers and more ambitious military ventures away from the group's base in the Sierra Maestra meant that each fighting column needed its own radio equipment . Eventually 32 Rebelde stations were operating throughout Cuba. The stations broadcast nightly, with each broadcast beginning with the loud declaration "¡Aquí Radio Rebelde!" ("Here's Radio Rebelde!") that has remained

9630-406: The recombination process prevails, since the gas molecules and ions are closer together. The balance between these two processes determines the quantity of ionization present. Ionization depends primarily on the Sun and its Extreme Ultraviolet (EUV) and X-ray irradiance which varies strongly with solar activity . The more magnetically active the Sun is, the more sunspot active regions there are on

9737-505: The sounds of instruments and existing musical recordings are altered by remixing or equalizing, with various distortions added, to replicate the garbled effects of shortwave radio reception. The first attempts by serious composers to incorporate radio effects into music may be those of the Russian physicist and musician Léon Theremin , who perfected a form of radio oscillator as a musical instrument in 1928 ( regenerative circuits in radios of

9844-436: The station's trademark salutation to the present day, followed by the Cuban national anthem and the 26th of July hymn. On April 9, 1958, the station broadcast calls for the nation's workers to join in a general strike . Rebelde also broadcast the first reports that Guevara's column had taken Santa Clara on New Year's Eve 1958, and on the first morning of the new year Castro broadcast a call for another general strike. During

9951-407: The sunspot cycle and geomagnetic activity. Geophysically, the state of the ionospheric plasma may be described by four parameters: electron density, electron and ion temperature and, since several species of ions are present, ionic composition . Radio propagation depends uniquely on electron density. Models are usually expressed as computer programs. The model may be based on basic physics of

10058-533: The term ionosphere in a letter published only in 1969 in Nature : We have in quite recent years seen the universal adoption of the term 'stratosphere'..and..the companion term 'troposphere'... The term 'ionosphere', for the region in which the main characteristic is large scale ionisation with considerable mean free paths, appears appropriate as an addition to this series. In the early 1930s, test transmissions of Radio Luxembourg inadvertently provided evidence of

10165-473: The time were prone to breaking into oscillation , adding various tonal harmonics to music and speech); and in the same year, the development of a French instrument called the Ondes Martenot by its inventor Maurice Martenot , a French cellist and former wireless telegrapher. Karlheinz Stockhausen used shortwave radio and effects in works including Hymnen (1966–1967), Kurzwellen (1968) – adapted for

10272-478: The topic of radio propagation of very long radio waves in the ionosphere. Vitaly Ginzburg has developed a theory of electromagnetic wave propagation in plasmas such as the ionosphere. In 1962, the Canadian satellite Alouette 1 was launched to study the ionosphere. Following its success were Alouette 2 in 1965 and the two ISIS satellites in 1969 and 1971, further AEROS-A and -B in 1972 and 1975, all for measuring

10379-404: The transmission he rejected any attempts by the Cuban military to replace Fulgencio Batista by a coup d'état and urged his revolutionary force to press on to the cities of Havana and Santiago . His final words were "¡Revolución Sí, Golpe Militar No!" (Revolution Yes, Military coup No!). Within hours the army had surrendered in full. In turn, Venezuelan broadcasts had the initiative to retransmit

10486-537: The variation of the electron density from bottom of the ionosphere to the altitude of maximum density than in describing the total electron content (TEC). Since 1999 this model is "International Standard" for the terrestrial ionosphere (standard TS16457). Ionograms allow deducing, via computation, the true shape of the different layers. Nonhomogeneous structure of the electron / ion - plasma produces rough echo traces, seen predominantly at night and at higher latitudes, and during disturbed conditions. At mid-latitudes,

10593-449: The visual horizon, about 64 km (40 miles). Shortwave broadcasts of radio programs played an important role in the early days of radio history. In World War II it was used as a propaganda tool for an international audience. The heyday of international shortwave broadcasting was during the Cold War between 1960 and 1980. With the wide implementation of other technologies for

10700-578: The war parts of Radio Rebelde through Radio Rumbos and Radio Continent, which allowed to know the advances of the Castro guerillas and the setbacks of the dictator Batista. Shortwave radio Shortwave radio is radio transmission using radio frequencies in the shortwave bands (SW). There is no official definition of the band range, but it always includes all of the high frequency band (HF) , which extends from 3 to 30 MHz (100 (exactly 99.930819333) to 10 (exactly 9.9930819333) meters); above

10807-414: The wavelengths in this band are shorter than 200 m (1,500 kHz) which marked the original upper limit of the medium frequency band first used for radio communications. The broadcast medium wave band now extends above the 200 m / 1,500 kHz limit. Early long-distance radio telegraphy used long waves, below 300  kilohertz (kHz) / above 1000 m. The drawbacks to this system included

10914-603: The world. On 10 October the Third National Radio Conference made three shortwave bands available to U.S. amateurs at 80 meters (3.75 MHz), 40 meters (7 MHz) and 20 meters (14 MHz). These were allocated worldwide, while the 10 meter band (28 MHz) was created by the Washington International Radiotelegraph Conference on 25 November 1927. The 15 meter band (21 MHz)

11021-960: Was detected by Edward V. Appleton and Miles Barnett . The E s layer ( sporadic E-layer) is characterized by small, thin clouds of intense ionization, which can support reflection of radio waves, frequently up to 50 MHz and rarely up to 450 MHz. Sporadic-E events may last for just a few minutes to many hours. Sporadic E propagation makes VHF-operating by radio amateurs very exciting when long-distance propagation paths that are generally unreachable "open up" to two-way communication. There are multiple causes of sporadic-E that are still being pursued by researchers. This propagation occurs every day during June and July in northern hemisphere mid-latitudes when high signal levels are often reached. The skip distances are generally around 1,640 km (1,020 mi). Distances for one hop propagation can be anywhere from 900 to 2,500 km (560 to 1,550 mi). Multi-hop propagation over 3,500 km (2,200 mi)

11128-548: Was opened to amateurs in the United States on 1 May 1952. Shortwave radio frequency energy is capable of reaching any location on the Earth as it is influenced by ionospheric reflection back to Earth by the ionosphere , (a phenomenon known as " skywave propagation"). A typical phenomenon of shortwave propagation is the occurrence of a skip zone where reception fails. With a fixed working frequency, large changes in ionospheric conditions may create skip zones at night. As

11235-472: Was possible on shortwave bands. Early long-distance services used surface wave propagation at very low frequencies , which are attenuated along the path at wavelengths shorter than 1,000 meters. Longer distances and higher frequencies using this method meant more signal loss. This, and the difficulties of generating and detecting higher frequencies, made discovery of shortwave propagation difficult for commercial services. Radio amateurs may have conducted

11342-405: Was technically illegal (but tolerated at the time as the authorities mistakenly believed that such frequencies were useless for commercial or military use), amateurs began to experiment with those wavelengths using newly available vacuum tubes shortly after World War I. Extreme interference at the longer edge of the 150–200 meter band – the official wavelengths allocated to amateurs by

11449-508: Was using this technique to monitor the atmosphere above Australia and Antarctica. The ionosphere is a shell of electrons and electrically charged atoms and molecules that surrounds the Earth, stretching from a height of about 50 km (30 mi) to more than 1,000 km (600 mi). It exists primarily due to ultraviolet radiation from the Sun . The lowest part of the Earth's atmosphere ,

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