DXing
Encyclopedia
DXing is the hobby of tuning in and identifying distant radio
or television
signals, or making two way radio contact with distant stations in amateur radio
, citizens' band radio
or other two way radio communications. Many DXers also attempt to receive written verifications of reception (sometimes referred to as "QSL
s" or "veries") from the stations heard. The name of the hobby comes from DX, telegraphic shorthand
for "distance" or "distant".
By the 1950s, and continuing through the mid 1970s, many of the most powerful North America
n "clear channel" stations such as KDKA
, WLW
, CKLW
, CHUM
, WABC
, WJR
, WLS
, WKBW
, KFI
, KAAY
, KSL and a host of border blaster
s from Mexico
pumped out Top 40 music played by popular disc jockey
s. As most smaller, local AM radio stations had to sign off at night, the big 50 kW stations had loyal listeners hundreds of miles away.
The popularity of DXing the medium-wave band has diminished as the popular music
formats quickly migrated to the clearer, though less propagating, FM radio beginning in the 1970s. Meanwhile, the MW band in the United States
was getting more and more crowded with new stations and existing stations receiving FCC authorization
to operate at night. In Canada
, just the opposite occurred as AM stations began moving to FM beginning in the 1980s and continuing through today.
Outside of the Americas and Australia, most AM radio broadcasting was in the form of synchronous networks of government-operated stations, operating with hundreds, even thousands of kilowatts of power. Still, the lower powered stations and occasional trans-oceanic signal were popular DX targets.
bands has been popular with both casual listeners and DXing hobbyists.
With the rise in popularity of streaming audio over the internet, many international broadcasters (including the BBC
and Voice of America
) have cut back on their shortwave broadcasts. Missionary
Religious broadcasters
still make extensive use of shortwave radio to reach less developed countries around the world.
In addition to international broadcasters, the shortwave bands also are home to military communications, RTTY
, amateur radio
, pirate radio
, and the mysterious broadcasts of numbers station
s. Many of these signals are transmitted in single side band mode, which requires the use of specialized receivers more suitable to DXing than to casual listening.
bands - especially those stations at the lower end of these bands - can "skip" for hundreds, even thousands of miles. American FM stations have been occasionally received in Western Europe
, though no reports exist of European FM signals propagating to North America.
Police, fire, and military communications on the VHF bands are also DX'ed to some extent on multi-band radio scanners, though they are mainly listened to strictly on a local basis. One difficulty is in identifying the exact origins of communications of this nature, as opposed to commercial broadcasters which must identify themselves at the top of each hour, and can often be identified through mentions of sponsors, slogans, etc. throughout their programming.
", today it generally means contacting amateur radio
stations in far-away places. On the HF
(also known as shortwave
) bands, DX stations are those in foreign countries
. On the VHF
/UHF
bands, DX stations can be within the same country
or continent
, since making a long-distance VHF contact, without the help of a satellite
, can be very difficult.
For award purposes, other areas than just political countries can be classified as "DX countries". For example, the French protectorate of Reunion Island in the Indian Ocean
is counted as a DX country, even though it is a region of France
. The rules for determining what is a DX country can be quite complex and to avoid potential confusion, radio amateurs often use the term entity instead of country. In addition to entities, some awards are based on island
groups in the world's oceans. On the VHF
/UHF
bands, many radio amateurs pursue awards based on Maidenhead grid locators.
For the most rare locations, DX-pedition
s are often organized to allow radio amateurs to "work a new one".
There are frequent contests
where radio amateurs operate their stations on certain dates for a fixed period of time to try to communicate with as many DX stations as possible.
In addition, many clubs offer awards for communicating with a certain number of DX stations. For example, the ARRL
offers the DX Century Club
award, or DXCC. The basic certificate is awarded for working and confirming at least 100 entities on the ARRL DXCC List.
Usually a QSL
card will have a picture on one side and the reception data on the other. Most of the broadcasters will use pictures and messages indicating their country's culture or technological life.
stands for the following qualities, graded on a scale of 1 to 5, where '1' means the quality was very bad and '5' very good.
S - Signal strength
I - Interference with other stations or broadcasters
N - Noise ratio in the received signal
P - Propagation (ups and downs of the reception)
O - Overall merit
Although this is a subjective measure, with practise the grading becomes more consistent, and a particular broadcast may be assessed by several listeners from the same area, in which case the broadcaster could assess correspondence between reports.
After listening to a broadcast, the listener writes a report with SINPO values, typically including his geographical location (called QTH in amateur radio teminology) in longitude and latitude, a brief description of the programme listened to, their opinion about it, suggestions if any, and so on.
The listener can send the report to the broadcaster either by post or email, and request verification (QSL) from them.
Variants of this report are:
a) the SIO report which omits the Noise and Propagation,
b) grading on a scale of 1 to 3 (instead of 1 to 5) and
c) the SINFO report where the F stands for fading.
to refract the transmitted radio
beam. The beam returns to the Earth's surface, and may then be reflected back into the ionosphere for a second bounce. Ionospheric refraction is generally only feasible for frequencies below about 50 MHz, and is highly dependent upon atmospheric conditions, the time of day, and the eleven-year sunspot
cycle. It is also affected by solar storm
s and some other solar events, which can alter the Earth's ionosphere by ejecting a shower of charged particles.
The angle of refraction places a minimum on the distance at which the refracted beam will first return to Earth. This distance increases with frequency. As a result, any station employing DX will be surrounded by an annular dead zone where they can't hear other stations or be heard by them.
This is the phenomenon that allows short wave radio reception to occur beyond the limits of line of sight. It is utilized by amateur radio
enthusiasts (hams), shortwave broadcast stations (such as BBC
and Voice of America
) and others. This is what allows you to hear AM (MW) stations from locations far from your location. It is one of the backups to failure of long distance communication by satellites, when their operation is affected by electromagnetic
storms from the sun.
Serious hobbyists use more elaborate receivers designed specifically for pulling in distant signals, and often build their own antennas specifically designed for a specific frequency band. There is much discussion and debate in the hobby about the relative merits of lesser priced shortwave receivers vs. their multi-thousand dollar "big brother" radios. In general, a good desktop or "PC Radio" will be able to "hear" just about what a very expensive high-performance receiver can receive. The difference between the two types comes into play during difficult band or reception conditions. The expensive receiver will have more filtering options and usually better adjacent channel interference blocking, sometimes resulting in the difference of being able to receive or not receive a signal under poor conditions. Reception of international broadcasting
seldom shows a noticeable difference between the two radios. An example of a high-end shortwave receiver currently being manufactured is the Ten-Tec RX-340.
Car radios
are also used for DXing the broadcast bands.
Another recent trend is for the hobbyist to employ multiple radios and antennas connected to a personal computer. Through advanced radio control software, the radios can be automatically ganged together, so that tuning one radio can tune all the others in the group. This DXing technique is sometimes referred to as diversity
reception and facilitates easy "A to B" comparison of different antennas and receivers for a given signal. For more details on "PC Radios" or computer controlled shortwave receivers see the discussion in Shortwave listening
.
Having a minimum of two Dipole antenna
at right angles to each other, for example, one running North-South and one running East-West can produce dramatically different reception patterns. These simple antennas can be made for a few dollars worth of wire and a couple of insulators.
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
or television
Terrestrial television
Terrestrial television is a mode of television broadcasting which does not involve satellite transmission or cables — typically using radio waves through transmitting and receiving antennas or television antenna aerials...
signals, or making two way radio contact with distant stations in amateur radio
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
, citizens' band radio
Citizens' band radio
Citizens' Band radio is, in many countries, a system of short-distance radio communications between individuals on a selection of 40 channels within the 27-MHz band. Citizens' Band is distinct from the FRS, GMRS, MURS and amateur radio...
or other two way radio communications. Many DXers also attempt to receive written verifications of reception (sometimes referred to as "QSL
QSL
QSL is one of the Q codes used in radiocommunication and radio broadcasting. A Q code message can stand for a statement or a question . In this case, QSL? means "do you confirm receipt of my transmission?" while QSL means "I confirm receipt of your transmission". Some also take it to mean "Query...
s" or "veries") from the stations heard. The name of the hobby comes from DX, telegraphic shorthand
Shorthand
Shorthand is an abbreviated symbolic writing method that increases speed or brevity of writing as compared to a normal method of writing a language. The process of writing in shorthand is called stenography, from the Greek stenos and graphē or graphie...
for "distance" or "distant".
AM radio DX
Early radio listeners, often using home made crystal sets and long wire antennas, found radio stations few and far between. With the broadcast bands uncrowded, signals of the most powerful stations could be heard over hundreds of miles, but weaker signals required more precise tuning or better receiving gear.By the 1950s, and continuing through the mid 1970s, many of the most powerful North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
n "clear channel" stations such as KDKA
KDKA (AM)
KDKA is a radio station licensed to Pittsburgh, Pennsylvania, USA. Created by the Westinghouse Electric Corporation on November 2, 1920, it is one of the world's first modern radio stations , a distinction that has also been challenged by other stations, although it has claimed to be the first in...
, WLW
WLW
WLW is a clear channel talk radio station located in Cincinnati, Ohio, run by Clear Channel Communications. The station broadcasts locally on 700 kHz AM...
, CKLW
CKLW
CKLW is a 50,000 watt AM radio station broadcasting on 800 kHz and located in Windsor, Ontario, Canada, and serving Windsor and Detroit. Additionally, its signal can be heard as far west as Belding, Michigan; as far east as Batavia, New York; as far south as Edgewood, Kentucky; and as far...
, CHUM
CHUM (AM)
CHUM, branded as TSN Radio 1050, broadcasting at 1050 kHz in the AM band, is a Canadian radio station licensed to Toronto, Ontario. The station is owned and operated by Bell Media....
, WABC
WABC (AM)
WABC , known as "NewsTalkRadio 77 WABC" is a radio station in New York City. Owned by the broadcasting division of Cumulus Media, the station broadcasts on a clear channel and is the flagship station of Cumulus Media Networks...
, WJR
WJR
WJR is a radio station in Detroit, Michigan, United States. It broadcasts a news/talk format. It is a class A clear channel station whose broadcasts can be heard throughout most of the Midwest, eastern United States and Canada at night, making it one of the most powerful radio stations in the...
, WLS
WLS (AM)
WLS is a Chicago clear-channel AM station on 890 kHz. It uses C-QUAM AM stereo and transmits with 50,000 watts from transmitter and towers on the south edge of Tinley Park, Illinois....
, WKBW
WWKB
WWKB is an AM radio station in Buffalo, New York that operates on a frequency of 1520 kHz. It is owned and operated by Entercom Communications. The station carries a progressive talk radio format. Declaring itself as A New Voice, A New Choice, The Voice of the New Majority; WWKB carries a number...
, KFI
KFI
KFI is an AM radio station in Los Angeles, California. It received its license to operate on March 31, 1922 and began operating on April 16, 1922 as one of the United States' first high-powered, "clear-channel" stations...
, KAAY
KAAY
KAAY is a 50,000-watt, class-A AM radio station in Little Rock, Arkansas, licensed on 1090 kHz.-History:KAAY was founded as KTHS in 1924 in Hot Springs; it moved to Little Rock in 1953. After the TV station KTHV was created from it in 1955, KTHS was sold to LIN Broadcasting, who turned it into...
, KSL and a host of border blaster
Border blaster
A border blaster is a licensed commercial radio station that transmits at very high power from one nation to another. Border blasters should not be confused with international broadcast stations...
s from Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
pumped out Top 40 music played by popular disc jockey
Disc jockey
A disc jockey, also known as DJ, is a person who selects and plays recorded music for an audience. Originally, "disc" referred to phonograph records, not the later Compact Discs. Today, the term includes all forms of music playback, no matter the medium.There are several types of disc jockeys...
s. As most smaller, local AM radio stations had to sign off at night, the big 50 kW stations had loyal listeners hundreds of miles away.
The popularity of DXing the medium-wave band has diminished as the popular music
Popular music
Popular music belongs to any of a number of musical genres "having wide appeal" and is typically distributed to large audiences through the music industry. It stands in contrast to both art music and traditional music, which are typically disseminated academically or orally to smaller, local...
formats quickly migrated to the clearer, though less propagating, FM radio beginning in the 1970s. Meanwhile, the MW band in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
was getting more and more crowded with new stations and existing stations receiving FCC authorization
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
to operate at night. In Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, just the opposite occurred as AM stations began moving to FM beginning in the 1980s and continuing through today.
Outside of the Americas and Australia, most AM radio broadcasting was in the form of synchronous networks of government-operated stations, operating with hundreds, even thousands of kilowatts of power. Still, the lower powered stations and occasional trans-oceanic signal were popular DX targets.
Shortwave DX
Especially during wartime and times of conflict, reception of international broadcasters, whose signals propagate around the world on the shortwaveShortwave
Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...
bands has been popular with both casual listeners and DXing hobbyists.
With the rise in popularity of streaming audio over the internet, many international broadcasters (including the BBC
BBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...
and Voice of America
Voice of America
Voice of America is the official external broadcast institution of the United States federal government. It is one of five civilian U.S. international broadcasters working under the umbrella of the Broadcasting Board of Governors . VOA provides a wide range of programming for broadcast on radio...
) have cut back on their shortwave broadcasts. Missionary
Missionary
A missionary is a member of a religious group sent into an area to do evangelism or ministries of service, such as education, literacy, social justice, health care and economic development. The word "mission" originates from 1598 when the Jesuits sent members abroad, derived from the Latin...
Religious broadcasters
Religious broadcasting
Religious broadcasting refers to broadcasting by religious organizations, usually with a religious message. Many religious organizations have long recorded content such as sermons and lectures, and have moved into distributing content on their Internet websites.While this article emphasises...
still make extensive use of shortwave radio to reach less developed countries around the world.
In addition to international broadcasters, the shortwave bands also are home to military communications, RTTY
Radioteletype
Radioteletype is a telecommunications system consisting originally of two or more electromechanical teleprinters in different locations, later superseded by personal computers running software to emulate teleprinters, connected by radio rather than a wired link.The term radioteletype is used to...
, amateur radio
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
, pirate radio
Pirate radio
Pirate radio is illegal or unregulated radio transmission. The term is most commonly used to describe illegal broadcasting for entertainment or political purposes, but is also sometimes used for illegal two-way radio operation...
, and the mysterious broadcasts of numbers station
Numbers station
A numbers station is a shortwave radio station of uncertain origin. In the 1950s, Time magazine reported that the numbers stations first appeared shortly after World War II and were using a format that had been used to send weather data during that war.Numbers stations generally broadcast...
s. Many of these signals are transmitted in single side band mode, which requires the use of specialized receivers more suitable to DXing than to casual listening.
VHF DXing
Though sporadic in nature, signals on the FM broadcast and VHF televisionTelevision
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
bands - especially those stations at the lower end of these bands - can "skip" for hundreds, even thousands of miles. American FM stations have been occasionally received in Western Europe
Western Europe
Western Europe is a loose term for the collection of countries in the western most region of the European continents, though this definition is context-dependent and carries cultural and political connotations. One definition describes Western Europe as a geographic entity—the region lying in the...
, though no reports exist of European FM signals propagating to North America.
Police, fire, and military communications on the VHF bands are also DX'ed to some extent on multi-band radio scanners, though they are mainly listened to strictly on a local basis. One difficulty is in identifying the exact origins of communications of this nature, as opposed to commercial broadcasters which must identify themselves at the top of each hour, and can often be identified through mentions of sponsors, slogans, etc. throughout their programming.
DX Station
Although the classic definition of DX is "distanceDistance
Distance is a numerical description of how far apart objects are. In physics or everyday discussion, distance may refer to a physical length, or an estimation based on other criteria . In mathematics, a distance function or metric is a generalization of the concept of physical distance...
", today it generally means contacting amateur radio
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
stations in far-away places. On the HF
High frequency
High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
(also known as shortwave
Shortwave
Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...
) bands, DX stations are those in foreign countries
Country
A country is a region legally identified as a distinct entity in political geography. A country may be an independent sovereign state or one that is occupied by another state, as a non-sovereign or formerly sovereign political division, or a geographic region associated with a previously...
. On the VHF
Very high frequency
Very high frequency is the radio frequency range from 30 MHz to 300 MHz. Frequencies immediately below VHF are denoted High frequency , and the next higher frequencies are known as Ultra high frequency...
/UHF
Ultra high frequency
Ultra-High Frequency designates the ITU Radio frequency range of electromagnetic waves between 300 MHz and 3 GHz , also known as the decimetre band or decimetre wave as the wavelengths range from one to ten decimetres...
bands, DX stations can be within the same country
Country
A country is a region legally identified as a distinct entity in political geography. A country may be an independent sovereign state or one that is occupied by another state, as a non-sovereign or formerly sovereign political division, or a geographic region associated with a previously...
or continent
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...
, since making a long-distance VHF contact, without the help of a satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
, can be very difficult.
For award purposes, other areas than just political countries can be classified as "DX countries". For example, the French protectorate of Reunion Island in the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
is counted as a DX country, even though it is a region of France
Régions of France
France is divided into 27 administrative regions , 22 of which are in Metropolitan France, and five of which are overseas. Corsica is a territorial collectivity , but is considered a region in mainstream usage, and is even shown as such on the INSEE website...
. The rules for determining what is a DX country can be quite complex and to avoid potential confusion, radio amateurs often use the term entity instead of country. In addition to entities, some awards are based on island
Island
An island or isle is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, cays or keys. An island in a river or lake may be called an eyot , or holm...
groups in the world's oceans. On the VHF
Very high frequency
Very high frequency is the radio frequency range from 30 MHz to 300 MHz. Frequencies immediately below VHF are denoted High frequency , and the next higher frequencies are known as Ultra high frequency...
/UHF
Ultra high frequency
Ultra-High Frequency designates the ITU Radio frequency range of electromagnetic waves between 300 MHz and 3 GHz , also known as the decimetre band or decimetre wave as the wavelengths range from one to ten decimetres...
bands, many radio amateurs pursue awards based on Maidenhead grid locators.
For the most rare locations, DX-pedition
DX-pedition
A DX-pedition is an expedition to what is considered an exotic place by amateur radio operators, perhaps because of its remoteness or because there are very few radio amateurs active from that place. This could be an island, a country, or even a particular spot on a geographical grid.The activity...
s are often organized to allow radio amateurs to "work a new one".
There are frequent contests
Contesting
Contesting is a competitive activity pursued by amateur radio operators. In a contest, an amateur radio station, which may be operated by an individual or a team, seeks to contact as many other amateur radio stations as possible in a given period of time and exchange information...
where radio amateurs operate their stations on certain dates for a fixed period of time to try to communicate with as many DX stations as possible.
In addition, many clubs offer awards for communicating with a certain number of DX stations. For example, the ARRL
American Radio Relay League
The American Radio Relay League is the largest membership association of amateur radio enthusiasts in the USA. ARRL is a non-profit organization, and was founded in May 1914 by Hiram Percy Maxim of Hartford, Connecticut...
offers the DX Century Club
DX Century Club
The DX Century Club, or DXCC, is an amateur radio operating award earned by making contact with 100 or more geographic entities around the world....
award, or DXCC. The basic certificate is awarded for working and confirming at least 100 entities on the ARRL DXCC List.
DX Clubs
Many radio enthusiasts are members of DX clubs. There are many DX clubs in many countries around the world. They are useful places to find information about up-to-date news relating to international radio. Many people also enjoy social events, which can form a large part of the enjoyment that people can get out of the radio hobby.QSL cards
One of the interesting sides of DXing as a hobby is collecting QSL cards (acknowledgement cards from the broadcaster) confirming the listener's reception report (sometimes called SINPO report, see next section).Usually a QSL
QSL
QSL is one of the Q codes used in radiocommunication and radio broadcasting. A Q code message can stand for a statement or a question . In this case, QSL? means "do you confirm receipt of my transmission?" while QSL means "I confirm receipt of your transmission". Some also take it to mean "Query...
card will have a picture on one side and the reception data on the other. Most of the broadcasters will use pictures and messages indicating their country's culture or technological life.
SINPO report
SINPOSINPO
SINPO, acronym for signal, interference, noise, propagation, and overall, is a code used to describe the quality of radio transmissions, especially in reception reports written by shortwave listeners...
stands for the following qualities, graded on a scale of 1 to 5, where '1' means the quality was very bad and '5' very good.
S - Signal strength
I - Interference with other stations or broadcasters
N - Noise ratio in the received signal
P - Propagation (ups and downs of the reception)
O - Overall merit
Although this is a subjective measure, with practise the grading becomes more consistent, and a particular broadcast may be assessed by several listeners from the same area, in which case the broadcaster could assess correspondence between reports.
After listening to a broadcast, the listener writes a report with SINPO values, typically including his geographical location (called QTH in amateur radio teminology) in longitude and latitude, a brief description of the programme listened to, their opinion about it, suggestions if any, and so on.
The listener can send the report to the broadcaster either by post or email, and request verification (QSL) from them.
Variants of this report are:
a) the SIO report which omits the Noise and Propagation,
b) grading on a scale of 1 to 3 (instead of 1 to 5) and
c) the SINFO report where the F stands for fading.
DX Communication
DX communication is communication over great distances using the ionosphereIonosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
to refract the transmitted radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
beam. The beam returns to the Earth's surface, and may then be reflected back into the ionosphere for a second bounce. Ionospheric refraction is generally only feasible for frequencies below about 50 MHz, and is highly dependent upon atmospheric conditions, the time of day, and the eleven-year sunspot
Sunspot
Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature....
cycle. It is also affected by solar storm
Solar storm
Solar storm can refer to:*Solar flare, a large explosion in the Sun's atmosphere*Coronal mass ejection , a massive burst of solar wind associated with solar flares*Geomagnetic storm, the interaction of the Sun's outburst with Earth's magnetic field...
s and some other solar events, which can alter the Earth's ionosphere by ejecting a shower of charged particles.
The angle of refraction places a minimum on the distance at which the refracted beam will first return to Earth. This distance increases with frequency. As a result, any station employing DX will be surrounded by an annular dead zone where they can't hear other stations or be heard by them.
This is the phenomenon that allows short wave radio reception to occur beyond the limits of line of sight. It is utilized by amateur radio
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
enthusiasts (hams), shortwave broadcast stations (such as BBC
BBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...
and Voice of America
Voice of America
Voice of America is the official external broadcast institution of the United States federal government. It is one of five civilian U.S. international broadcasters working under the umbrella of the Broadcasting Board of Governors . VOA provides a wide range of programming for broadcast on radio...
) and others. This is what allows you to hear AM (MW) stations from locations far from your location. It is one of the backups to failure of long distance communication by satellites, when their operation is affected by electromagnetic
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
storms from the sun.
DXing equipment
Radio equipment used in DXing ranges from inexpensive portable receivers to deluxe equipment costing thousands of dollars. Using just a simple AM radio, one can easily hear signals from the most powerful stations propagating hundreds of miles at night. Even an inexpensive shortwave radio can receive signals emanating from several countries during any time of day.Serious hobbyists use more elaborate receivers designed specifically for pulling in distant signals, and often build their own antennas specifically designed for a specific frequency band. There is much discussion and debate in the hobby about the relative merits of lesser priced shortwave receivers vs. their multi-thousand dollar "big brother" radios. In general, a good desktop or "PC Radio" will be able to "hear" just about what a very expensive high-performance receiver can receive. The difference between the two types comes into play during difficult band or reception conditions. The expensive receiver will have more filtering options and usually better adjacent channel interference blocking, sometimes resulting in the difference of being able to receive or not receive a signal under poor conditions. Reception of international broadcasting
International broadcasting
International broadcasting is broadcasting that is deliberately aimed at a foreign, rather than a domestic, audience. It usually is broadcast by means of longwave, mediumwave, or shortwave radio, but in recent years has also used direct satellite broadcasting and the Internet as means of reaching...
seldom shows a noticeable difference between the two radios. An example of a high-end shortwave receiver currently being manufactured is the Ten-Tec RX-340.
Car radios
Car audio
Car audio/video , auto radio, mobile audio, 12-volt and other terms are used to describe the sound or video system fitted in an automobile. While 12-volt audio and video systems are also used, marketed, or manufactured for marine, aviation, and buses, this article focuses on cars as the most common...
are also used for DXing the broadcast bands.
Another recent trend is for the hobbyist to employ multiple radios and antennas connected to a personal computer. Through advanced radio control software, the radios can be automatically ganged together, so that tuning one radio can tune all the others in the group. This DXing technique is sometimes referred to as diversity
Diversity scheme
In telecommunications, a diversity scheme refers to a method for improving the reliability of a message signal by using two or more communication channels with different characteristics. Diversity plays an important role in combatting fading and co-channel interference and avoiding error bursts...
reception and facilitates easy "A to B" comparison of different antennas and receivers for a given signal. For more details on "PC Radios" or computer controlled shortwave receivers see the discussion in Shortwave listening
Shortwave listening
Shortwave listening is the hobby of listening to shortwave radio broadcasts located on frequencies between 1700 kHz and 30 MHz. Listeners range from casual users seeking international news and entertainment programming to hobbyists immersed in the technical aspects of radio reception and DXing...
.
Having a minimum of two Dipole antenna
Dipole antenna
A dipole antenna is a radio antenna that can be made of a simple wire, with a center-fed driven element. It consists of two metal conductors of rod or wire, oriented parallel and collinear with each other , with a small space between them. The radio frequency voltage is applied to the antenna at...
at right angles to each other, for example, one running North-South and one running East-West can produce dramatically different reception patterns. These simple antennas can be made for a few dollars worth of wire and a couple of insulators.
External links
- ARRL - American Radio Relay league.
- DX Info for radioamateurs