500 kHz

The radio frequency of 500 kilohertz (500 kHz) has been an international calling and distress frequency for Morse code maritime communication since early in the 20th century. The unit kilohertz was not introduced until the 1960s. 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 December 1999. 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. Proposals to allocate frequencies at or near 500 kHz to amateur radio use resulted in the creation of the 630-meter band.

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).[1][2]

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 seagoing 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 transmitters. 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 codes" specified by the 1912 Service Regulations.

SS Jeremiah O'Brien LF radio.agr
500 kHz transmitter and receiver position on SS Jeremiah O'Brien, a World War II Liberty ship

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" to exchange messages once contact was established. 425, 454, 468, 480, and 512 kHz were used by ships while the coast stations had their own individual working frequencies. 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.

Ship's radio room clock with silence periods marked

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 the 2182 kHz voice communications distress signals. In addition, during this silent period all coastal and ship stations were required to monitor the frequency, listening for any distress signals.[3] All large ships at sea had to monitor 500 kHz at all times, either with a licensed radio operator or with equipment (called an auto-alarm) that automatically detected an SOS alarm signal.

Simulated auto-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

Regions with a 500 kHz amateur radio allocation. Blue indicates official allocations based on WRC-12. Light blue indicates official allocations that are outside the WRC-12 frequencies. Green indicates experimental allocations. Operation is prohibited in red regions.

With maritime traffic largely displaced from 500 kHz band, some countries have taken steps to allocate frequencies at or near 500 kHz to amateur radio use. In Belgium, amateurs are allocated a 501 to 504 kHz segment on a secondary basis on January 15, 2008. Only CW may be used with a maximum ERP of 5 W.[4] In Norway, the band segment 493–510 kHz was allocated to radio amateurs on November 6, 2009. Only radiotelegraphy is permitted.[5] In New Zealand, the band segment of 505 to 515 kHz was allocated temporarily, pending an international frequency allocation.[6] In the Netherlands Amateur radio operators have allocated the band segment from 501–505 kHz with a maximum of 100 watts PEP on January 1, 2012.[7]

See also


  1. ^ Ken Beauchamp; Institution of Electrical Engineers (January 2001). History of Telegraphy. IET. pp. 256–. ISBN 978-0-85296-792-8.
  2. ^ Anton A. Huurdeman (31 July 2003). The Worldwide History of Telecommunications. John Wiley & Sons. pp. 358–. ISBN 978-0-471-20505-0.
  3. ^ Ships and the Sea. Kalmbach Publishing Co. 1954.
  4. ^ Colin Thomas, G3PSM; Hans Timmerman, PB2T (2010-11-19). "500 kHz". IARU Region 1. Retrieved 2011-02-25.
  5. ^ "Forskrift om radioamatørlisens (Amateur Radio Regulations)". www.lovdata.no (in Norwegian). Lovdata. Retrieved 2009-11-08.
  6. ^ Roy Symon, ZL2KH (2010-02-24). "2010 NZ Amateurs Granted Access to 600 metre Band". NZART. Retrieved 2011-02-25.
  7. ^ "Regeling van de Minister van Economische Zaken, Landbouw en Innovatie van 20 december 2011, nr. AT-EL&I/6621235, tot wijziging van de Regeling gebruik van frequentieruimte zonder vergunning 2008 in verband met de implementatie van twee besluiten van de Commissie van de Europese Gemeenschappen en het vergunningvrij maken van het gebruik van grond- en muur penetrerende radar" (in Dutch). overheid.nl. 2012-12-30. Retrieved 2012-01-03.

External links

2182 kHz

The radio frequency 2182 kHz is one of the international calling and distress frequencies for maritime radiocommunication in a frequency band allocated to the mobile service on primary basis, exclusively for distress and calling operations.

630-meter band

The 630 meter (or 600 meter) amateur radio band is a frequency band allocated by the International Telecommunication Union (ITU) to amateur radio operators, and it ranges from 472 to 479 kHz, or equivalently 625.9 to 635.1 meters wavelength. It was formally allocated to amateurs at the 2012 World Radiocommunication Conference (WRC-12). The band is available on a secondary basis in all ITU regions with the limitation that amateur stations have maximum radiated power of 1 Watt effective isotropic radiated power (EIRP); however, stations more than 800 km from certain countries may be permitted to use 5 Watts EIRP.The new WRC-12 allocation did not take formal effect until 1 January 2013. However, several countries previously allocated the WRC-12 band to amateurs domestically. Previously, several other countries have authorized temporary allocations or experimental operations on nearby frequencies.

The band is in the Medium Frequency (MF) region, within the greater 415–526.5 kHz maritime band.

Auroral kilometric radiation

Auroral kilometric radiation (AKR) is the intense radio radiation emitted in the acceleration zone (at a height of three times the radius of the Earth) of the polar lights. The radiation mainly comes from cyclotron radiation from electrons orbiting around the magnetic field lines of the Earth. The radiation has a frequency of between 50 and 500 kHz and a total power of between about 1 million and 10 million watts. The radiation is absorbed by the ionosphere and therefore can only be measured by satellites positioned at vast heights, such as the Fast Auroral Snapshot Explorer (FAST). According to the data of the Cluster mission, it is beamed out in the cosmos in a narrow plane tangent to the magnetic field at the source. The sound produced by playing AKR over an audio device has been described as "whistles", "chirps", and even "screams".

As some other planets emit cyclotron radiation too, AKR could be used to learn more about Jupiter, Saturn, Uranus and Neptune, and to detect extrasolar planets.

Automated Maritime Telecommunications System

Automated Maritime Telecommunications System (AMTS) is a commercial mobile radio service used within the United States. It operates within the VHF frequency range, just above the North American Band III television range, and offers both voice and data communications to maritime customers. The system is operated by a network of private carriers across the country, with coverage primarily including coastal and inland waterways.

Bucket-brigade device

A bucket brigade or bucket-brigade device (BBD) is a discrete-time analogue delay line, developed in 1969 by F. Sangster and K. Teer of the Philips Research Labs. It consists of a series of capacitance sections C0 to Cn. The stored analogue signal is moved along the line of capacitors, one step at each clock cycle. The name comes from analogy with the term bucket brigade, used for a line of people passing buckets of water.

In most signal processing applications, bucket brigades have been replaced by devices that use digital signal processing, manipulating samples in digital form. Bucket brigades still see use in specialty applications, such as guitar effects.

A well-known integrated circuit device around 1980, the Reticon SAD-1024 implemented two 512-stage analog delay lines in a 16-pin DIP. It allowed clock frequencies ranging from 1.5 kHz to more than 1.5 MHz. The SAD-512 was a single delay line version. The Philips Semiconductors TDA1022 similarly offered a 512-stage delay line but with a clock rate range of 5–500 kHz. Other common BBD chips include the Panasonic MN3005, MN3007 and MN3205, with the primary differences being the available delay time.

In 2009, the guitar effects pedal manufacturer Visual Sound recommissioned production of the Panasonic-designed MN3102 and MN3207 BBD chip that it offers for sale.Despite being analog in their representation of individual signal voltage samples, these devices are discrete in the time domain and thus are limited by the Nyquist–Shannon sampling theorem; both the input and output signals are generally low-pass filtered. The input must be low-pass filtered to avoid aliasing effects, while the output is low-pass filtered for reconstruction. (A low-pass is used as an approximation to the Whittaker–Shannon interpolation formula.)

The concept of the bucket-brigade device led to the charge-coupled device (CCD) developed by Bell Labs.

CCIR System B

CCIR System B was the 625-line analog broadcast television system which at its peak was the system used in most countries. It is being replaced across Western Europe, part of Asia and Africa by digital broadcasting.

CCIR System G

CCIR System G is an analog broadcast television system used in many countries. There are several systems in use and letter G is assigned for the European UHF system which is also used in the majority of Asian and African countries. (However some countries in Europe use different systems.)

CCIR System H

CCIR System H is an analog broadcast television system primarily used in Belgium, the Balkans and Malta on the UHF bands.


The EDUC-8, pronounced "educate", was an early microcomputer kit published by Electronics Australia in a series of articles starting in August 1974 and continuing to August 1975. Electronics Australia initially believed that it was the first such kit, but later discovered that Radio-Electronics had just beaten it with their Mark-8 by one month. However, Electronics Australia staff believed that their TTL design was superior to the Mark-8, as it did not require the purchase of an expensive microprocessor chip.

The EDUC-8 was an 8 bit bit-serial design with 256 bytes of RAM. The internal clock speed was 500 kHz, with an instruction speed of approximately 10 kHz, due to the bit-serial implementation. The instruction set was based on the DEC PDP-8.

Unlike the MITS Altair 8800, the EDUC-8 included two serial input and two serial output ports at the back of the computer. The EDUC-8 also had front panel lights and switches to program the computer. The later articles included a variety of peripherals, allowing the computer to interface to a keypad, octal display, paper tape loader, paper tape puncher, printer, keyboard, music player, teleprinter, magnetic tape recorder and alphanumeric display. The articles were collected into a book, where additional information was published detailing how to expand the number of I/O ports to 256, adding up to 32KB of additional memory, and using the computer to control various switches.

Medium frequency

Medium frequency (MF) is the ITU designation for radio frequencies (RF) in the range of 300 kilohertz (kHz) to 3 megahertz (MHz). Part of this band is the medium wave (MW) AM broadcast band. The MF band is also known as the hectometer band as the wavelengths range from ten to one hectometer (1,000 to 100 m). Frequencies immediately below MF are denoted low frequency (LF), while the first band of higher frequencies is known as high frequency (HF). MF is mostly used for AM radio broadcasting, navigational radio beacons, maritime ship-to-shore communication, and transoceanic air traffic control.

Power-line communication

Power-line communication (PLC) carries data on a conductor that is also used simultaneously for AC electric power transmission or electric power distribution to consumers. It is also known as power-line carrier, power-line digital subscriber line (PDSL), mains communication, power-line telecommunications, or power-line networking (PLN).

A wide range of power-line communication technologies are needed for different applications, ranging from home automation to Internet access which is often called broadband over power lines (BPL). Most PLC technologies limit themselves to one type of wires (such as premises wiring within a single building), but some can cross between two levels (for example, both the distribution network and premises wiring). Typically transformers prevent propagating the signal, which requires multiple technologies to form very large networks. Various data rates and frequencies are used in different situations.

A number of difficult technical problems are common between wireless and power-line communication, notably those of spread spectrum radio signals operating in a crowded environment. Radio interference, for example, has long been a concern of amateur radio groups.


The R1155 was a British communications receiver, commonly used in aircraft along with its associated T1154 transmitter. It was used extensively by the Royal Air Force during World War II, mainly in larger aircraft such as the Avro Lancaster, Handley Page Halifax, Vickers Wellington and Short Sunderland. Some were also used in vehicles and air-sea rescue launches.

The R1155 and T1154 sets were manufactured by several British radio manufacturers, including EKCO, Marconi, Plessey, and EMI. Ekco, who manufactured the R1155 and T1154 at its Aylesbury shadow factory, carried out extensive development work on both units before putting them into production, significantly improving on the original Marconi design.

Large numbers of war surplus R1155 radios were modified for private use postwar.

Radio silence

In telecommunications, radio silence or Emissions Control (EMCON) is a status in which all fixed or mobile radio stations in an area are asked to stop transmitting for safety or security reasons.

The term "radio station" may include anything capable of transmitting a radio signal. A single ship, aircraft, spacecraft, or group of them may also maintain radio silence.

Radiofrequency ablation

Radiofrequency ablation (RFA) is a medical procedure in which part of the electrical conduction system of the heart, tumor or other dysfunctional tissue is ablated using the heat generated from medium frequency alternating current (in the range of 350–500 kHz). RFA is generally conducted in the outpatient setting, using either local anesthetics or conscious sedation anesthesia. When it is delivered via catheter, it is called radiofrequency catheter ablation.

Two important advantages of radio frequency current (over previously used low frequency AC or pulses of DC) are that it does not directly stimulate nerves or heart muscle and therefore can often be used without the need for general anesthetic, and that it is very specific for treating the desired tissue without significant collateral damage.Documented benefits have led to RFA becoming widely used during the 21st century. RFA procedures are performed under image guidance (such as X-ray screening, CT scan or ultrasound) by an interventional pain specialist (such as an anesthesiologist), interventional radiologist, otolaryngologists, a gastrointestinal or surgical endoscopist, or a cardiac electrophysiologist, a subspecialty of cardiologists.


SOS is the International Morse code distress signal (▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄); the overscore indicates that the normal gaps between the letters should be omitted. It is used as a start-of-message mark for transmissions requesting help when loss of life or catastrophic loss of property is imminent. Other prefixes are assigned for mechanical breakdowns, requests for medical assistance, and a relayed distress signal originally sent by another station.

This distress signal was first adopted by the German government radio regulations effective 1 April 1905, and became the worldwide standard under the second International Radiotelegraphic Convention, which was signed on 3 November 1906, and became effective on 1 July 1908. SOS remained the maritime radio distress signal until 1999, when it was replaced by the Global Maritime Distress and Safety System. SOS is still recognized as a standard distress signal that may be used with any signaling method.The SOS distress signal is a continuous sequence of three dots, three dashes, and three dots, with no spaces between the letters (notated by the overscore). In International Morse Code, three dots form the letter S, and three dashes make the letter O, so "S O S" became a way to remember the order of the dots and dashes. In modern terminology, SOS is a Morse "procedural signal" or "prosign", and the formal way to write it is with a bar above the letters or enclosed in angle brackets: SOS or .

Even though SOS does not stand for anything, in popular usage it became associated with such phrases as "Save Our Souls" and "Save Our Ship". SOS is only one of several ways that the combination could have been written; for example, IWB, VZE, 3B, or V7 all produce exactly the same sound; SOS is just the easiest to remember.

Side-scan sonar

Side-scan sonar (also sometimes called side scan sonar, sidescan sonar, side imaging sonar, side-imaging sonar and bottom classification sonar) is a category of sonar system that is used to efficiently create an image of large areas of the sea floor.

System Module

System Modules (originally known as System Building Blocks; the name was changed around 1961) are a DEC modular digital logic family which preceded the later FLIP CHIPs. They connect to the units they are plugged into via a set of 22 gold-plated discrete pins along one edge.They use transistor inverter circuits, with the transistors operating saturated, to avoid dependence on tight tolerances; they use -3V and 0V as logic levels. Intended for prototyping as well as production, they include design features intended to avoid damage. They are provided with design advice which includes loading rules and wiring instructions.They were available in three compatible speed lines:

4000-Series: the basic series, speeds range from 500 KHz to 1 MHz

1000-Series: for use where extra standard output loads, or -3V sources, are needed

6000-Series: higher speeds, 5 MHz to 10 MhzIn addition, special modules were available for purposes such as I/O converters (to standard internal voltages), bus drivers, lamp and solenoid drivers, A/D conversion, relays, core memory drivers, etc.Larger assemblies which are part of the same family provide core memory testing devices, and there are also power supplies, mounting panels with slots for the modules, cabinets to hold groups of mounting panels,indicator light panels, etc, etc.

Texas Instruments SN76489

The SN76489 Digital Complex Sound Generator (DCSG) is a TTL-compatible programmable sound generator chip from Texas Instruments. It contains:

3 square wave tone generators.

A wide range of frequencies.

16 different volume levels.

1 noise generator.

2 types (white noise and periodic).

3 different frequencies.

16 different volume levels.Its main application was the generation of music and sound effects in game consoles, arcade games and home computers (such as the Texas Instruments TI-99/4A, BBC Micro, ColecoVision, and IBM PCjr), competing with the similar General Instrument AY-3-8910.

Yaesu FT-7(B)


Yaesu FT-7 is a rugged, solid state and modular built HF amateur-band radio transceiver, suitable for fixed and for mobile operation. The set was built by the Yaesu Corporation in Japan in the late 1970s and early 1980s. Its first Japanese release was in 1976. This transceiver was very small for its time; by current modern standards however it is a large mobile set. It is a low-power (QRP) SSB and CW transceiver of which transmitting power is adjustable up from 10 to about 20 W. The set is built up with pre-dated synthesisers and microprocessors, has an excellent receiver and a perfect dynamic range with good close-in noise performance which makes tuning across the noisy 80 or 40 m bands at night very easy. All features, coupled to a price of $260- (in 1976) made sure that the "Fox Tango 7" as it was known became very popular in the HAM world.

In 1979 its somewhat upgraded successor – the Yaesu FT-7B – was released and as of 1980 this rig was also sold on the European market. FT-7B has fully extended 10 m band coverage in four 500 kHz segments (this was limited to a single 500 kHz segment in the original FT-7 version). The FT-7B also offers Amplitude Modulation (AM) mode. Its transmitting output is adjustable from 5 to 50 W maximum by an integrated 50 W power amplifier using two 2SC2099 final transistors. It is also equipped with a noise blanker and an RF attenuator. It is a compliment to its manufacturers that even nowadays more than 30 years later FT-7(B)’s are still popular and are often used as a secondary or as a back-up transceiver.

In Europe the sets were imported by the Swiss firm Sommerkamp and sold as Sommerkamp FT-7(B).

Amateur and hobbyist
(aeronautical mobile)
Land-based commercial
and government mobile
Marine (shipboard)
Signaling /
Selective calling
System elements
and principles
Network topology
and switching

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