International distress frequency
Encyclopedia
Since early in the 20th century, the radio frequency of 500 kilohertz (500 kHz) has been an international calling and distress frequency
for Morse code
maritime communication. The unit kilohertz was not introduced until 1960. For most of its history, the international distress frequency was referred to by its equivalent wavelength
, 600 meters, or, using the earlier frequency unit name, 500 kilocycles [per second] or 500 kc.
The United States Coast Guard
and comparable agencies of other nations used to maintain 24-hour watches on this frequency, staffed by highly skilled radio operators. Many SOS
calls and medical emergencies at sea were handled here until the late 1980s. However, because of the near disappearance of the commercial use of Morse code, the frequency is now rarely used. Emergency traffic on 500 kHz has been almost completely replaced by the Global Maritime Distress Safety System
(GMDSS). Beginning in the late 1990s, most nations ended monitoring of transmissions on 500 kHz. The nearby frequencies of 518 kHz and 490 kHz are used for the Navtex
component of GMDSS. There have been proposals to allocate frequencies at or near 500 kHz to amateur radio
use.
The Service Regulations, affixed to the 1912 Convention, established 500 kHz as the primary frequency for sea-going communication, and the standard ship frequency was changed from 1,000 kHz to 500 kHz, to match the coastal station standard. Communication was generally conducted in Morse code
, initially using spark-gap transmitter
s. Most two-way radio contacts were to be initiated on this frequency, although once established the participating stations could shift to another frequency to avoid the congestion on 500 kHz. To facilitate communication between operators speaking different languages, standardized abbreviations were used including a set of "Q code
s" specified by the 1912 Service Regulations.
Article XXI of the Service Regulations required that whenever an SOS distress call was heard, all transmissions unrelated to the emergency had to immediately cease until the emergency was declared over. There was a potential problem if a ship transmitted a distress call: The use of 500 kHz as a common frequency often led to heavy congestion, especially around major ports and shipping lanes, and it was possible the distress message would be drowned out by the bedlam of ongoing commercial traffic. To help address this problem, the Service Regulation's Article XXXII specified that: "Coastal stations engaged in the transmission of long radiograms shall suspend the transmission at the end of each period of 15 minutes, and remain silent for a period of three minutes before resuming the transmission. Coastal and shipboard stations working under the conditions specified in Article XXXV, par. 2, shall suspend work at the end of each period of 15 minutes and listen in with a wave length of 600 meters during a period of three minutes before resuming the transmission." During distress working all non-distress traffic was banned from 500 kHz and adjacent coast stations then monitored 512 kHz as an additional calling frequency for ordinary traffic.
International refinements for the use of 500 kHz were specified in later agreements, including the 1932 Madrid Radio Conference. In later years, except for distress traffic, stations shifted to nearby "working frequencies" (425, 454, 468, 480, and 512 kHz) to exchange messages once contact was established. Twice each hour, all stations operating on 500 kHz were required to maintain a strictly enforced three-minute silent period, starting at 15 and 45 minutes past the hour.
As a visual memory aid, a typical clock in a ship's radio room would have the silence periods marked by shading the sectors
between h+15 to h+18 and h+45 to h+48 in RED. Similar sectors between h+00 to H+03 and h+30 to h+33 are marked in GREEN which is the corresponding silence period for 2182 kHz
. In addition, during this silent period all coastal and ship stations were required to monitor the frequency, listening for any distress signals. All large ships at sea had to monitor 500 kHz at all times, either with a licensed radio operator or with equipment that detected an automatic alarm signal. Shore stations throughout the world operated on this frequency to exchange messages with ships and to issue warning about weather and other navigational warnings. At night, transmission ranges of 3,000–4,000 miles (4,500–6,500 kilometers) were typical. Daytime ranges were much shorter, on the order of 300–1500 miles (500–2,500 kilometers). Terman's Radio Engineering Handbook (1948) shows the maximum distance for 1 kW over salt water to be 1,500 miles, and this distance was routinely covered by ships at sea, where signals from ships and nearby coastal stations would cause congestion, covering up distant and weaker signals. During the silence, a distress signal could more easily be heard at great distances.
use. In Belgium
, amateurs are allocated a 501 to 504 kHz on a secondary basis on January 15, 2008. Only CW may be used with a maximum ERP of 5W. In Norway
, the band 493–510 kHz was allocated to radio amateurs on November 6, 2009. Only radiotelegraphy is permitted. In New Zealand
, the band of 505 to 515 kHz was allocated temporarily, pending an international frequency allocation.
Other regions have granted experimental uses for selected licensees in advance of any international frequency allocation. The U.S.
Federal Communications Commission
(FCC) granted the American Radio Relay League
an experimental license to explore such uses in September 2006. Subsequently, the UK
started to issue Special Research Permits for amateurs to use 501–504 kHz. Ireland
has allowed individuals to apply for Test Licenses in the 501 to 504 kHz frequency range. Canada
has allowed individuals to apply for use in the 504 to 509 kHz frequency range. Other regions with experimental allocations include Croatia
, Czech Republic
, Denmark
, Iceland
, Netherlands
, Sweden
, and Spain
.
Germany
has allowed experimental propagation beacons on 505.1 kHz, but does not have an amateur allocation that would allow two-way contacts.
During the 2012 World Radiocommunication Conference
(WRC-12) of the International Telecommunication Union
, a 15 kHz allocation to the amateur radio service will be considered on a secondary use basis. The specific frequencies are yet to be determined, but are expected to be between 415 kHz and 526.5 kHz.
International distress frequency
Since early in the 20th century, the radio frequency of 500 kilohertz has been an international calling and distress frequency for Morse code maritime communication. The unit kilohertz was not introduced until 1960...
for Morse code
Morse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...
maritime communication. The unit kilohertz was not introduced until 1960. For most of its history, the international distress frequency was referred to by its equivalent wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
, 600 meters, or, using the earlier frequency unit name, 500 kilocycles [per second] or 500 kc.
The United States Coast Guard
United States Coast Guard
The United States Coast Guard is a branch of the United States Armed Forces and one of the seven U.S. uniformed services. The Coast Guard is a maritime, military, multi-mission service unique among the military branches for having a maritime law enforcement mission and a federal regulatory agency...
and comparable agencies of other nations used to maintain 24-hour watches on this frequency, staffed by highly skilled radio operators. Many SOS
SOS
SOS is the commonly used description for the international Morse code distress signal...
calls and medical emergencies at sea were handled here until the late 1980s. However, because of the near disappearance of the commercial use of Morse code, the frequency is now rarely used. Emergency traffic on 500 kHz has been almost completely replaced by the Global Maritime Distress Safety System
Global Maritime Distress Safety System
The Global Maritime Distress and Safety System is an internationally agreed-upon set of safety procedures, types of equipment, and communication protocols used to increase safety and make it easier to rescue distressed ships, boats and aircraft....
(GMDSS). Beginning in the late 1990s, most nations ended monitoring of transmissions on 500 kHz. The nearby frequencies of 518 kHz and 490 kHz are used for the Navtex
Navtex
NAVTEX is an international automated medium frequency direct-printing service for delivery of navigational and meteorological warnings and forecasts, as well as urgent marine safety information to ships...
component of GMDSS. There have been proposals to allocate frequencies at or near 500 kHz 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...
use.
Initial adoption
International standards for the use of 500 kHz first appeared in the second Berlin International Radiotelegraphic Convention, which was signed November 3, 1906 and became effective July 1, 1908. The second Service Regulation affixed to this Convention designated 500 kHz as one of the standard frequencies to be employed by shore stations, specifying that "Two wave lengths, one of 300 meters [1 Mc/s] and the other of 600 meters, are authorized for general public service. Every coastal station opened to such service shall use one or the other of these two wave lengths." (These regulations also specified that ship stations normally used 1 MHz).Expanded policies
International standards for the use of 500 kHz were expanded by the Third International Radiotelegraphic Convention, which was held after the sinking of the RMS Titanic. This Convention, meeting in London, produced an agreement which was signed on July 5, 1912, and became effective July 1, 1913.The Service Regulations, affixed to the 1912 Convention, established 500 kHz as the primary frequency for sea-going communication, and the standard ship frequency was changed from 1,000 kHz to 500 kHz, to match the coastal station standard. Communication was generally conducted in Morse code
Morse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...
, initially using spark-gap transmitter
Spark-gap transmitter
A spark-gap transmitter is a device for generating radio frequency electromagnetic waves using a spark gap.These devices served as the transmitters for most wireless telegraphy systems for the first three decades of radio and the first demonstrations of practical radio were carried out using them...
s. Most two-way radio contacts were to be initiated on this frequency, although once established the participating stations could shift to another frequency to avoid the congestion on 500 kHz. To facilitate communication between operators speaking different languages, standardized abbreviations were used including a set of "Q code
Q code
The Q code is a standardized collection of three-letter message encodings, also known as a brevity code, all of which start with the letter "Q", initially developed for commercial radiotelegraph communication, and later adopted by other radio services, especially amateur radio...
s" specified by the 1912 Service Regulations.
Article XXI of the Service Regulations required that whenever an SOS distress call was heard, all transmissions unrelated to the emergency had to immediately cease until the emergency was declared over. There was a potential problem if a ship transmitted a distress call: The use of 500 kHz as a common frequency often led to heavy congestion, especially around major ports and shipping lanes, and it was possible the distress message would be drowned out by the bedlam of ongoing commercial traffic. To help address this problem, the Service Regulation's Article XXXII specified that: "Coastal stations engaged in the transmission of long radiograms shall suspend the transmission at the end of each period of 15 minutes, and remain silent for a period of three minutes before resuming the transmission. Coastal and shipboard stations working under the conditions specified in Article XXXV, par. 2, shall suspend work at the end of each period of 15 minutes and listen in with a wave length of 600 meters during a period of three minutes before resuming the transmission." During distress working all non-distress traffic was banned from 500 kHz and adjacent coast stations then monitored 512 kHz as an additional calling frequency for ordinary traffic.
Later policies
The silent and monitoring periods were soon expanded and standardized. For example, Regulation 44, from the July 27, 1914 edition of "Radio Communication Laws of the United States", stated: "The international standard wave length is 600 meters, and the operators of all coast stations are required, during the hours the station is in operation, to 'listen in' at intervals of not more than 15 minutes and for a period not less than 2 minutes, with the receiving apparatus tuned to receive this wave length, for the purpose of determining if any distress signals or messages are being sent and to determine if the transmitting operations of the 'listening station' are causing interference with other radio communication."International refinements for the use of 500 kHz were specified in later agreements, including the 1932 Madrid Radio Conference. In later years, except for distress traffic, stations shifted to nearby "working frequencies" (425, 454, 468, 480, and 512 kHz) to exchange messages once contact was established. Twice each hour, all stations operating on 500 kHz were required to maintain a strictly enforced three-minute silent period, starting at 15 and 45 minutes past the hour.
Circular sector
A circular sector or circle sector, is the portion of a disk enclosed by two radii and an arc, where the smaller area is known as the minor sector and the larger being the major sector. In the diagram, θ is the central angle in radians, r the radius of the circle, and L is the arc length of the...
between h+15 to h+18 and h+45 to h+48 in RED. Similar sectors between h+00 to H+03 and h+30 to h+33 are marked in GREEN which is the corresponding silence period for 2182 kHz
2182 kHz
The radio frequency of 2182 kHz is the international calling and distress frequency for maritime radiotelephone communications on the marine MF bands.- Transmission modes :...
. In addition, during this silent period all coastal and ship stations were required to monitor the frequency, listening for any distress signals. All large ships at sea had to monitor 500 kHz at all times, either with a licensed radio operator or with equipment that detected an automatic alarm signal. Shore stations throughout the world operated on this frequency to exchange messages with ships and to issue warning about weather and other navigational warnings. At night, transmission ranges of 3,000–4,000 miles (4,500–6,500 kilometers) were typical. Daytime ranges were much shorter, on the order of 300–1500 miles (500–2,500 kilometers). Terman's Radio Engineering Handbook (1948) shows the maximum distance for 1 kW over salt water to be 1,500 miles, and this distance was routinely covered by ships at sea, where signals from ships and nearby coastal stations would cause congestion, covering up distant and weaker signals. During the silence, a distress signal could more easily be heard at great distances.
Amateur radio
With maritime traffic largely displaced from 500 kHz band, some countries have taken steps to allocate frequencies at or near 500 kHz to amateur radioAmateur 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...
use. In Belgium
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...
, amateurs are allocated a 501 to 504 kHz on a secondary basis on January 15, 2008. Only CW may be used with a maximum ERP of 5W. In Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
, the band 493–510 kHz was allocated to radio amateurs on November 6, 2009. Only radiotelegraphy is permitted. In New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, the band of 505 to 515 kHz was allocated temporarily, pending an international frequency allocation.
Other regions have granted experimental uses for selected licensees in advance of any international frequency allocation. The U.S.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
Federal Communications Commission
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...
(FCC) granted the American Radio Relay League
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...
an experimental license to explore such uses in September 2006. Subsequently, the UK
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
started to issue Special Research Permits for amateurs to use 501–504 kHz. Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
has allowed individuals to apply for Test Licenses in the 501 to 504 kHz frequency range. 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...
has allowed individuals to apply for use in the 504 to 509 kHz frequency range. Other regions with experimental allocations include Croatia
Croatia
Croatia , officially the Republic of Croatia , is a unitary democratic parliamentary republic in Europe at the crossroads of the Mitteleuropa, the Balkans, and the Mediterranean. Its capital and largest city is Zagreb. The country is divided into 20 counties and the city of Zagreb. Croatia covers ...
, Czech Republic
Czech Republic
The Czech Republic is a landlocked country in Central Europe. The country is bordered by Poland to the northeast, Slovakia to the east, Austria to the south, and Germany to the west and northwest....
, Denmark
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
, Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
, Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
, Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
, and Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
.
Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
has allowed experimental propagation beacons on 505.1 kHz, but does not have an amateur allocation that would allow two-way contacts.
During the 2012 World Radiocommunication Conference
World Radiocommunication Conference
World Radiocommunication Conference is organized by ITU to review, and, as necessary, revise the Radio Regulations, the international treaty governing the use of the radio-frequency spectrum and the geostationary-satellite and non-geostationary-satellite orbits. It is held every three to four years...
(WRC-12) of the International Telecommunication Union
International Telecommunication Union
The International Telecommunication Union is the specialized agency of the United Nations which is responsible for information and communication technologies...
, a 15 kHz allocation to the amateur radio service will be considered on a secondary use basis. The specific frequencies are yet to be determined, but are expected to be between 415 kHz and 526.5 kHz.
See also
- 2182 kHz2182 kHzThe radio frequency of 2182 kHz is the international calling and distress frequency for maritime radiotelephone communications on the marine MF bands.- Transmission modes :...
— the international distress frequency for voice maritime communication, and still in use as such - Aircraft emergency frequencyAircraft emergency frequencyThe aircraft emergency frequency is a frequency used on the aircraft radio band reserved for emergency communications for aircraft in distress. The frequencies are 121.5 MHz for civilian, also known as International Air Distress and 243.0 MHz for military use, also known as Military Air...
- Call for helpCall for HelpCall for Help, also known as CFH, was a computer-themed television program that first aired exclusively on TechTV , a cable and satellite television network focused on technology, and then aired on G4techTV Canada and the HOW TO Channel in Australia...
for emergency frequencies in current use. - GMDSS
- Maritime mobile amateur radioMaritime mobile amateur radioMost countries' amateur radio licences allow licensed operators to install and use radio transmission equipment while at sea. Such operation is known as maritime mobile amateur radio...
- Medium frequency radio propagation
- Radio Act of 1912Radio Act of 1912The Radio Act of 1912 is a United States federal law that mandated that all radio stations in the US be licensed by the federal government, as well as mandating that seagoing vessels continuously monitor distress frequencies....
- Radio propagationRadio propagationRadio propagation is the behavior of radio waves when they are transmitted, or propagated from one point on the Earth to another, or into various parts of the atmosphere...
External links
- Berlin International Radiotelegraphic Convention of 1906
- Radio Laws and Regulations of the United States: Edition July 27, 1914. (Includes the 1912 London Radiotelegraphic Convention)
- Excellent first hand account of distress frequency communications
- Proposal for experimental amateur radio access to 500 kHz by the Radio Society of Great BritainRadio Society of Great BritainFirst founded in 1913 as the London Wireless Club, the Radio Society of Great Britain is the United Kingdom's recognised national society for amateur radio operators. The society's patron is Prince Philip, Duke of Edinburgh and it represents the interests of the UK’s 60,000 licensed radio amateurs...
- The 500 KC Experimental Group for Amateur Radio
- International Telecommunication Union
- Marine and Coastguard Agency
- Merchant Shipping Regulations