Amateur radio direction finding (ARDF, also known as radio orienteering, radio fox hunting and radiosport) is an amateur racing sport that combines radio direction finding with the map and compass skills of orienteering. It is a timed race in which individual competitors use a topographic map, a magnetic compass and radio direction finding apparatus to navigate through diverse wooded terrain while searching for radio transmitters. The rules of the sport and international competitions are organized by the International Amateur Radio Union. The sport has been most popular in Eastern Europe, Russia, and China, where it was often used in the physical education programs in schools.
ARDF events use radio frequencies on either the two-meter or eighty-meter amateur radio bands. These two bands were chosen because of their universal availability to amateur radio licensees in all countries. The radio equipment carried by competitors on a course must be capable of receiving the signal being transmitted by the five transmitters and useful for radio direction finding, including a radio receiver, attenuator, and directional antenna. Most equipment designs integrate all three components into one handheld device.
History
Nations that have participated in major international competitions since the first European Championship in 1961
The sport originated in Northern Europe and Eastern Europe in the late 1950s. Amateur radio was widely promoted in the schools of Northern and Eastern Europe as a modern scientific and technical activity. Most medium to large cities hosted one or more amateur radio clubs at which members could congregate and learn about the technology and operation of radio equipment. One of the activities that schools and radio clubs promoted was radio direction finding, an activity that had important civil defense applications during the Cold War. As few individuals in Europe had personal automobiles at the time, most of this radio direction finding activity took place on foot, in parks, natural areas, or school campuses. The sport of orienteering, popular in its native Scandinavia, had begun to spread to more and more countries throughout Europe, including the nations of the Eastern Bloc. As orienteering became more popular and orienteering maps became more widely available, it was only natural to combine the two activities and hold radio direction finding events on orienteering maps.
Interest in this kind of on-foot radio direction finding activity using detailed topographic maps for navigation spread throughout Scandinavia, Eastern and Central Europe, the Soviet Union, and the People's Republic of China. Formal rules for the sport were first proposed in England and Denmark in the 1950s.[3][unreliable source?] The first European Championship in the sport was held in 1961 in Stockholm, Sweden. Four additional international championships were held in Europe in the 1960s, and three more were held in the 1970s. The first World Championship was held in 1980 in Cetniewo, Poland, where competitors from eleven European and Asian countries participated. World Championships have been generally held in even-numbered years since 1984, although there was no World Championship in 1996, and there was a World Championship in 1997. Asian nations began sending national teams to international events in 1980, and teams from nations in Oceania and North America began competing in the 1990s. Athletes from twenty-six nations attended the 2000 World Championship in Nanjing, China, the first to be held outside of Europe.[dead link][4]
As the sport grew in the 1960s and 1970s, each nation devised its own set of rules and regulations. The need for more clearly defined and consistent rules for international competitions led to the formation of an ARDF working group by the International Amateur Radio Union (IARU) in the late 1970s. The first ARDF event to use the new standardized rules was the 1980 World Championship. These rules have been revised and updated over the years, increasing the number of gender and age categories into which competitors are classified, as well as formalizing the start and finish line procedures.[5][unreliable source?] While some variations exist, these standardized rules have since been used worldwide for ARDF competitions, and the IARU has become the principal international organization promoting the sport. The IARU divides the world into three regions for administrative purposes. These regions correspond with the three regions used by the International Telecommunication Union for its regulatory purposes, but the IARU has also used these regions for sports administration. The first IARU RegionI (Europe, Africa, the Middle East, and ex-USSR) Championship was held in 1993 in Chtelnica, Slovakia,[dead link][4] the first IARU RegionIII (Asia and Oceania) Championship was held in 1993 in Beijing, China,[dead link][6] and the first IARU RegionII (North and South America) Championship was held in 1999 in Portland, Oregon, USA.[5] In addition to participation in international events, most nations with active ARDF organizations hold annual national championships using the IARU rules.
ARDF is a sport that spans much of the globe. In 2012 over 570 athletes from thirty-three countries, representing four continents, entered the 16th World Championships held in Kopaonik, Serbia [7] Organized ARDF competitions can be found in almost every European country and in all the nations of northern and eastern Asia. ARDF activity is also found in Thailand, Australia, New Zealand, Canada, and the United States. Although they represent a broad range of amateur radio interests in their nations today, several member societies of the International Amateur Radio Union were originally formed for the promotion and organization of the sport and continue to use the term radiosport in their society name. These include the Federation of Radiosport of the Republic of Armenia (FRRA),[8] the Belarusian Federation of Radioamateurs and Radiosportsmen (BFRR),[9] the Chinese Radio Sports Association (CRSA),[10] and the Mongolian Radio Sport Federation (MRSF).[11] To promote the sport, the IARU has delegated individuals as ARDF Coordinators for each IARU region to help educate and organize national radio societies and other ARDF groups, especially in nations without prior activity in the sport.
Description of competition and rules
The rules used throughout the world, with minor variations, are maintained by the IARU RegionI ARDF Working Group.[12] Although these rules were developed specifically for international competitions, they have become the de facto standard used as the basis for all international competitions worldwide.
An ARDF competition normally takes place in diverse wooded terrain, such as in a public park or natural area but competitions have also been held in suitable suburban areas. Each competitor receives a detailed topographic map of the competition area. The map will indicate the location of the start with a triangle and the location of the finish with two concentric circles. Somewhere within the competition area designated on the map, the meet organizer will have placed five low power radio transmitters. The locations of the transmitters are kept a secret from the competitors and are not marked on the map. Each transmitter emits a signal in Morse code by which it is easily identifiable to the competitors. The transmitters automatically transmit one after another in a repeating cycle. Depending on entry classification, a competitor will attempt to locate as many as three, four, or all five of the transmitters in the woods, and then travel to the finish line in the shortest possible time. Competitors start at staggered intervals, are individually timed, and are expected to perform all radio direction finding and navigation skills on their own. Standings are determined first by the number of transmitters found, then by shortest time on course. Competitors who take longer than the specified time limit to finish may be disqualified.
ARDF events use radio frequencies on either the 2-meter or 80-meter amateur radio bands. These two bands were chosen because of their universal availability to amateur radio licensees in all countries. Each band requires different radio equipment for transmission and reception, and requires the use of different radio direction finding skills. Radio direction finding equipment for eighty meters, an HF band, is relatively easy to design and inexpensive to build. Bearings taken on eighty meters can be very accurate. Competitors on an eighty-meter course must use bearings to determine the locations of the transmitters and choose the fastest route through the terrain to visit them. Two meters, a VHF band, requires equipment that is relatively more complicated to design and more expensive to build. Radio signals on two meters are more affected by features of the terrain. Competitors on a two-meter course must learn to differentiate between accurate, direct bearings to the source of the radio signal and false bearings resulting from reflections of the signal off hillsides, ravines, buildings, or fences. Large national or international events will have one day of competition using a 2-meter frequency and one day of competition using an 80-meter frequency.[3]
In addition to the rules of the sport, ARDF competitions must also comply with radio regulations. Because the transmitters operate on frequencies assigned to the Amateur Radio Service, a radio amateur with a license that is valid for the country in which the competition is taking place must be present and responsible for their operation. Individual competitors, however, are generally not required to have amateur radio licences, as the use of simple handheld radio receivers does not typically require a license. Regulatory prohibitions on the use of amateur radio frequencies for commercial use generally preclude the awarding of monetary prizes to competitors. Typical awards for ARDF events are medals, trophies, plaques, or certificates.
Entry categories
Although all competitors at an ARDF event use the same competition area and listen to the same set of five transmitters, they do not all compete in the same category. Current IARU rules divide entrants into different categories based on their age and gender. Only the M21 category must locate all five transmitters, while the other categories may skip only a specified transmitter or transmitters.
M19—Men ages 19 and younger, 4 or 5 transmitters
M21—Men of any age, 5 transmitters
M40—Men ages 40 and older, 4 or 5 transmitters
M50—Men ages 50 and older, 4 or 5 transmitters
M60—Men ages 60 and older, 3 or 4 transmitters
M70—Men ages 70 and older, 3 or 4 transmitters
W19—Women ages 19 and younger, 4 or 5 transmitters
W21—Women of any age, 4 or 5 transmitters
W35—Women ages 35 and older, 4 or 5 transmitters
W45—Women ages 45 and older, 3 or 4 transmitters
W55—Women ages 55 and older, 3 or 4 transmitters
W65—Women ages 65 and older, 3 or 4 transmitters
Youth competitions
The International Amateur Radio Union rules for ARDF competitions include provisions for youth competitions. These competitions are restricted to competitors aged sixteen years or younger. The course lengths are shorter (up to six kilometers), the transmitters may be located closer to the start (500meters), and a course setter may require that fewer transmitters be located.[13]
Since 2017, there is World Youth ARDF Championship (WYAC) every year. Participating categories in these championships are W14, W16, M14 and M16.
The IARU rules go into great detail about certain procedures that are unique to international championships events. Not every ARDF competition follows all of these rules. Common variations to the generally accepted rules exist at local events. Most smaller events do not have large juries or on-course referees. Some events will use simpler start procedures, such as using only one starting corridor instead of two. ARDF events on the two meter band in North America sometimes use frequency modulation instead of amplitude modulation for the transmission of the Morse code identifications.[16]
Map and course details
A portion of an orienteering map marked for an ARDF competition. Here, labeled circles indicate the locations of two of the five transmitters, but these do not appear on the maps given to competitors.
Ideally, the topographic maps used in ARDF competitions are created using the International Specification for Orienteering Maps 2000 (ISOM) [17] set by the International Orienteering Federation and used for orienteering competitions. In fact, many ARDF competitions use existing orienteering maps, in collaboration with the orienteering clubs that created those maps.
Course design is an important element of a successful competition. The international rules adopted by the IARU include both requirements and recommendations for basic course design. Important requirements are that no transmitter may be within 750meters of the start, no transmitter may be within 400meters of the finish or any other transmitter on course, and that there is no more than 200meters elevation change between the start, finish, and all transmitters. The IARU rules for international competitions recommend that courses be designed for six to ten kilometers of total travel distance through the terrain.[13] A well-designed course will present the competitors with an athletic challenge in addition to the challenges of land navigation and radio direction finding. Depending on the course design and competition, winning times at World Championship events are often less than 90minutes for two meter courses, and can be under 60minutes for eighty meter courses.[18]
Equipment and clothing
ARDF equipment is a specialty market, and much of what is available for purchase comes from small commercial vendors or small-batch production by individuals. Building equipment, such as handheld antennas, from published designs or kits is also a popular activity.[19] Clothing and other equipment is sold through specialty orienteering equipment suppliers or general outdoor sports retailers.
Transmitter equipment
A transmitter, orienteering control flag, paper punch and electronic punch device at an ARDF control.
ARDF transmitters have a low power output and operate in either the two meter or eighty meter amateur radio band. The transmissions are in Morse code. Each transmitter sends a unique identification that can be easily interpreted even by those unfamiliar with the Morse code by counting the number of dits that follow a series of dashes. The transmitters on course all transmit on the same frequency and each transmit in sequence for one minute at a time in a repeating cycle. Within a few meters of each transmitter, an orienteering control flag and punch device will be present. For many events and all major events, the punch device is an electronic system, such as SPORTident, used in orienteering competitions. This records the time competitors visit each control on a small device that they carry. An alternative is to use pin punches which the competitor uses to make a distinct pattern on a control card they carry. Competitors need to locate the control flag at the transmitter site and use the punch device to record their visit. Good course design will attempt to preclude, as much as possible, runners interfering with the transmitter equipment as they approach the control. At large international or national events, jurors might be present at transmitter controls to ensure fair play.
The IARU rules include detailed technical specifications for transmitter equipment.[13] Transmitters for two meters are typically 0.25 to 1watts power output, and use keyed amplitude modulation. The transmitter antennas used on two meters must be horizontally polarized and omnidirectional. Transmitters for eighty meters are typically one to five watts power output keyed CW modulation. The transmitter antennas used on eighty meters must be vertically polarized and omnidirectional. It is common for the transmitter, a battery, and any controlling hardware to be placed inside a weatherproof container such as an old ammunition case or large plastic food storage container for protection from the elements and wildlife.
Receiver equipment
The radio equipment carried on course must be capable of receiving the signal being transmitted by the five transmitters and useful for radio direction finding. This includes a radio receiver that can tune in the specific frequency of transmission being used for the event, an attenuator or variable gain control, and a directional antenna. Directional antennas are more sensitive to radio signals arriving from some directions than others. Most equipment designs integrate all three components into one handheld device. On the two meter band, the most common directional antennas used by competitors are two or three element Yagi antennas made from flexible steel tape. This kind of antenna has a cardioidreceiving pattern, which means that it has one peak direction where the received signal will be the strongest, and a null direction, 180° from the peak, in which the received signal will be the weakest. Flexible steel tape enables the antenna elements to flex and not break when encountering vegetation in the forest. On the eighty meter band, two common receiver design approaches are to use either a small loop antenna or an even smaller loop antenna wound around a ferrite rod. These antennas have a bidirectional receiving pattern, with two peak directions 180° apart from one another and two null directions 180° apart from one another. The peak directions are 90° offset from the null directions. A small vertical antenna element can be combined with the loop or ferrite rod antenna to change the receiving pattern to a cardioid shape, but the resulting null in the cardioid is not as sensitive as the nulls in the bidirectional receiving pattern. A switch is often used to allow the competitor to select the bidirectional or cardioid patterns at any moment. ARDF receiver equipment is designed to be lightweight and easy to operate while the competitor is in motion as well as rugged enough to withstand use in areas of thick vegetation.
Clothing
The IARU rules specify that the choice of clothing is an individual decision of the competitor, unless the meet director specifies otherwise.[13] Although comfortable outdoor clothing is all that is required for participation, specialty clothing developed for the sport of orienteering is also worn by ARDF competitors. Nylon pants, shirts, or suits, gaiters or padded socks for lower leg protection, and specialty shoes for cross-country running through wooded terrain are popular choices. Some competitors may choose to carry food or water on course, and wear a small waist pack or hydration pack for this purpose. At large international or national events, competitors may be required by the meet director to wear identifying numbers pinned to their clothing, and many wear team uniforms in their national colors.
Other equipment
In addition to the radio equipment and topographic map, an ARDF competitor uses a magnetic compass for navigation. The most popular compass types are those that are also popular for use in orienteering. Some events may require or suggest that competitors carry a whistle for emergency use. In at least one World Championship event, competitors were provided with cards written in the native language of the host country, intended to aid in communications with local citizens in the event that a competitor needed emergency aid or directions. In general, the use of cellular phone, or two-way radio equipment on course is prohibited.[13] All competitors are encouraged to wear a watch to keep track of their time on course and not finish over the time limit set for the competition.
Variations
Sprint events have shorter courses with an expected winning time of 15 minutes and use either a 1:5000 or 1:4000 map. They use lower powered transmitters on the eighty meter band which transmit in sequence for only 12seconds with the cycle repeating every minute. The IARU Region 1 Rules [20] require 2 sets of 5 transmitters where each set operates on a different frequency. The Morse code transmitted by the second set of transmitters is slightly faster (PARIS 70) than the first set (PARIS 50) to differentiate the two sets. There is also a "spectator" control and a "beacon" control which both operate on different frequencies to the other ten, so four frequencies are used in total. It is possible to combine the spectator control with the beacon control. Competitors start at 2 min intervals and have to visit between 3 and 5 controls out of the first set (according to their age class) before visiting the compulsory spectator control. They then visit the requisite controls from the second set before punching the compulsory beacon control, prior to finishing.
Fox Oring is a variation of the sport that requires more orienteering skills. In a Fox Oring course, the radio transmitters put out very little power, and can be received over only very short distances, often no more than 100meters. The location of each transmitter will be indicated on the map with a circle. The transmitter does not need to be exactly at the circle's center or even located inside the circle, but one should be able to receive its transmissions everywhere within the area indicated by the circle. A competitor must use orienteering skills to navigate to the area of the circle on the map and only then use radio direction finding skills to locate the very low power transmitter.[21]
Another variation of the sport, Radio Orienteering in a Compact Area, requires less athletic skill and more technical radio direction finding skills. In a ROCA course, the transmitters put out very little power, typically 10 to 200mW, and can be received over only very short distances. The transmitters are physically small, and marked with a control card that is no larger than a typical postcard with a unique number identification. Because of the low power and short distances involved, most ROCA competitors walk the entire course, and focus their attention on the radio direction finding tasks rather than navigation.[22][unreliable source?]
Another form of recreational radio direction finding activity in North America that includes the use of automobiles for transportation is most often referred to as foxhunting or transmitter hunting, but is sometimes confused with the organized international sport of amateur radio direction finding.
Orienteering is a group of sports that involve using a map and compass to navigate from point to point in diverse and usually unfamiliar terrain whilst moving at speed. Participants are given a topographical map, usually a specially prepared orienteering map, which they use to find control points. Originally a training exercise in land navigation for military officers, orienteering has developed many variations. Among these, the oldest and the most popular is foot orienteering. For the purposes of this article, foot orienteering serves as a point of departure for discussion of all other variations, but almost any sport that involves racing against a clock and requires navigation with a map is a type of orienteering.
The International Amateur Radio Union (IARU) is an international confederation of national organisations that allows a forum for common matters of concern to amateur radio operators worldwide, and collectively represents matters to the International Telecommunication Union (ITU). The International Amateur Radio Union was founded in 1925 and, as of July 2021, it is composed of 172 national member societies.
160-meter band refers to the band of radio frequencies between 1.8 and 2 MHz, just above the medium wave broadcast band. For many decades the lowest radio frequency band allocated for use by amateur radio, before the adoption, at the beginning of the 21st century in most countries, of the 630- and 2200-meter bands. Amateur operators often refer to 160 meters as the Top Band It is also sometimes nicknamed the "Gentleman's Band" in contrast to the often-freewheeling activity in the 80-, 40- and 20-meter bands.
The 80 meter or 3.5 MHz band is a span of radio frequencies allocated for amateur use, from 3.5–4.0 MHz in North and South America ; generally 3.5–3.8 MHz in Europe, Africa, and northern Asia (Region 1); and 3.5–3.9 MHz in south and east Asia and the eastern Pacific (Region 3). The upper portion of the band, which is usually used for phone (voice), is sometimes referred to as 75 meters; however, in Europe, "75 m" is used to name an overlapping shortwave broadcast band between 3.9–4.0 MHz used by a number of national radio services.
The 20-meter or 14-MHz amateur radio band is a portion of the shortwave radio spectrum, comprising frequencies stretching from 14.000 MHz to 14.350 MHz. The 20-meter band is widely considered among the best for long-distance communication (DXing), and is one of the most popular—and crowded—during contests. Several factors contribute to this, including the band's large size, the relatively small size of antennas tuned to it and its good potential for daytime DX operation even in unfavorable propagation conditions.
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. Rules for each competition define the amateur radio bands, the mode of communication that may be used, and the kind of information that must be exchanged. The contacts made during the contest contribute to a score by which stations are ranked. Contest sponsors publish the results in magazines and on web sites.
Radiosport is formal competition among amateur radio operators in any of three amateur radio activities: ARDF, DXing, and Contesting. The Friendship Radiosport Games is an international multi-sport event that includes all three types of radiosport. Since 1977, the International Amateur Radio Union has sponsored the IARU HF World Championship. The World Radiosport Team Championship is another international competition.
The World Radiosport Team Championship is an amateur radio competition. Participation is by invitation only. Entry to each quadrennial WRTC requires qualification through high positions in major world radio contests. The main principle of the WRTC is to provide a level playing field for the qualified contestants from around the world to compete against one another using amateur radio stations located in areas with the same propagation terrain and equipped with identical antennas, operating under the keen eyes of qualified referees. Each WRTC event is organised by a volunteer group of Radio Amateurs in the locality where the competition will be held with the help of a standing committee of internationally recognized contesters. The WRTC is the closest thing to a world championship in the sport of radio contesting. In 2018 over 1000 people are involved with a cost of over half a million Euros. WRTC2018 web page
Transmitter hunting, is an activity wherein participants use radio direction finding techniques to locate one or more radio transmitters hidden within a designated search area. This activity is most popular among amateur radio enthusiasts, and one organized sport variation is known as amateur radio direction finding.
The Friendship Radiosport Games (FRG) is an international multi-sport event that includes competitions in the various sports collectively referred to as radiosport. The Friendship Radiosport Games began in 1989 as a result of a sister city agreement between Khabarovsk, Russia and Portland, Oregon, United States. Since then, participation has been extended to other sister cities in the Pacific Rim. The Friendship Radiosport Games are generally held in the month of August.
Fox Oring is a variation of the sport of Amateur Radio Direction Finding. Fox Oring is a timed race in which individual competitors use a topographic map and a magnetic compass to navigate through diverse, wooded terrain while searching for radio transmitters. The term is derived from the use of the term fox hunting to describe recreational radio direction finding activity and an abbreviation of the word orienteering.
Radio Orienteering in a Compact Area is a variation of Amateur Radio Direction Finding. ROCA is a timed race in which individual competitors use a topographic map and a magnetic compass to navigate through diverse, wooded terrain while searching for radio transmitters.
An amateur radio station is a radio station designed to provide radiocommunications in the amateur radio service for an amateur radio operator. Radio amateurs build and operate several types of amateur radio stations, including fixed ground stations, mobile stations, space stations, and temporary field stations. A slang term often used for an amateur station's location is the shack, named after the small enclosures added to the upperworks of naval ships to hold early radio equipment and batteries.
An amateur radio propagation beacon is a radio beacon, whose purpose is the investigation of the propagation of radio signals. Most radio propagation beacons use amateur radio frequencies. They can be found on LF, MF, HF, VHF, UHF, and microwave frequencies. Microwave beacons are also used as signal sources to test and calibrate antennas and receivers.
The Chinese Radio Sports And Orienteering Association (CRSAOA) is a national non-profit organization for amateur radio enthusiasts in the People's Republic of China. The CRSA's primary mission is to popularize and promote amateur radio in China. Early activities of the organization focused on radiosport, and the CRSA was active in promoting Amateur Radio Direction Finding and High Speed Telegraphy competitions throughout the country. Although the CRSA has broadened its scope and now supports many kinds of radio activities, the organization's name continues to reflect this early heritage. Key membership benefits of the organization include QSL bureau services, a quarterly membership magazine called Ham's CQ. CRSA was also responsible for the administration of the amateur radio license certification program in the People's Republic of China until 2010.Former Chinese Radio Sports Association.
A control point is a marked waypoint used in orienteering and related sports such as rogaining and adventure racing. It is located in the competition area; marked both on an orienteering map and in the terrain, and described on a control description sheet. The control point must be identifiable on the map and on the ground. A control point has three components: a high visibility item, known as a flag or kite; an identifier, known as a control code; and a recording mechanism for contestants to record proof that they visited the control point. The control point is usually temporary, except on a permanent orienteering course.
Mountain bike orienteering is an orienteering endurance racing sport on a mountain bike where navigation is done along trails and tracks. Compared with foot orienteering, competitors usually are not permitted to leave the trail and track network. Navigation tactics are similar to ski-orienteering, where the major focus is route choice while navigating. The main difference compared to ski-orienteering is that navigation is done at a higher pace, because the bike can reach higher speeds. As the biker reaches higher speeds, map reading becomes more challenging.
The Kazakhstan Federation of Radiosport and Radio Amateur is a national non-profit organization for amateur radio enthusiasts in Kazakhstan. KFRR promotes amateur radio in Kazakhstan by sponsoring amateur radio operating awards and radio contests. The KFRR organizes and supports Amateur Radio Direction Finding competitions and the Kazakhstan national ARDF team. The KFRR also represents the interests of Kazakhstan amateur radio operators before Kazakhstan and international telecommunications regulatory authorities. KFRR is the national member society representing Kazakhstan in the International Amateur Radio Union, which it joined on February 10, 2009.
In amateur radio, high-speed telegraphy (HST) is a form of radiosport that challenges amateur radio operators to accurately receive and copy, and in some competitions to send, Morse code transmissions sent at very high speeds. This event is most popular in Eastern Europe. The International Amateur Radio Union (IARU) sponsors most of the international competitions.
Underwater orienteering, also known as scuba orienteering is an underwater sport that uses recreational open circuit scuba diving equipment and consists of a set of individual and team events conducted in both sheltered and open water testing the competitors' competency in underwater navigation. The competition is principally concerned with the effectiveness of navigation technique used by competitors to swim an underwater course following a route marked on a map prepared by the competition organisers, a compass and a counter meter to measure the distance covered. The sport was developed in the Soviet Union during the late 1950s and is played mainly in Europe. It is known as Orientation Sub in French and as La Orientación Subacuática in Spanish. Historically, the sport has also been known as Technical Disciplines.
References
Cited references
↑ "Tracking a concealed transmitter"(PDF). The Wireless World and Radio Review. Vol.XIX. July 7 – December 29, 1926. pp.83–84. Retrieved 2 February 2023.
↑ "To the day of Radio - "Fox Hunting", 1957". Retro. Weekly Geekly. Archived from the original on 2019-07-10. ...It all started with an article in the popular magazine Wireless World, dated July 21, 1926. This article was called "Tracking a concealed transmitter (Shefield Society's exciting field day)...
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