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What's Up With "10-4" And Other Radio Lingo?

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Reader and frequent question-asker Nate J. wrote in wondering why we say things like "10-4" and "Roger" on walkie-talkies and other two-way radios.

The Ten-Codes

The ten-codes or ten-signals are code words used as stand-ins for common phrases in radio communication. Charles Hopper, a communications director with the Illinois State Police, developed them in 1937 to combat the problem of the first syllables or words of a transmission being cut off or misunderstood. Preceding every code with "ten" gave the sometimes slow equipment time to warm up and improved the likelihood that a listener would understand the important part of a message. The codes also allowed for brevity and standardization in radio message traffic.

The codes were expanded by the Association of Public-Safety Communications Officials-International (APCO) in 1974 and were used by both law enforcement agencies and civilian CB radio users. Over time, differing meanings for the codes came about in different agencies and jurisdictions, undoing the codes' usefulness as a concise and standardized system. The problem came to a head in 2005 during rescue operations after Hurricane Katrina. After several instances of inter-agency communication problems, the United States Federal Emergency Management Agency (FEMA) discouraged the use of ten-codes and today the federal government recommends they be replaced with plain, everyday language. Here's the official APCO list.

Roger That

In the days of the telegraph, the Morse code letter R (dot-dash-dot) was sometimes used to indicate "received" or "message received/understood." When radio voice communication began to replace telegraphs, Roger, the code word assigned to the letter R in the Joint Army/Navy Phonetic Alphabet (the radio alphabet used by all branches of the United States military from 1941 to 1956), took on the same role.

Contrary to what Hollywood would have you think, Roger only means "last transmission received/understood" and does not also mean or imply "I will comply." Wilco (Will Comply) is the code used if the speaker intends to convey "message received and will comply." Given that, the phrase Roger Wilco, which you so often hear in the movies, is redundant and not really used since Wilco alone covers all the bases and acknowledges receipt of message and states intent to comply.


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Mayday is an international code word used to signal life-threatening emergencies. It was originated in 1923 by Frederick Stanley Mockford, a senior radio officer at London's Croydon Airport. He was given the task of coming up with a unique and easily understandable emergency code word. Most of the air traffic at Croydon was either coming from or going to Le Bourget Airport in Paris, so Mockford chose mayday because of its similarity to the French m'aider ("come help me").

Because it is an emergency signal, there are plenty of rules governing the use and format of a mayday call. A mayday call can only be made when life or craft is in imminent danger of death or destruction (and, as with fake 9-1-1 calls, fake mayday calls are considered serious crimes. In the U.S., making a fake distress call is a federal crime that can carry large fines and jail time), and once one is made, no other messages can be transmitted except to assist in the emergency.

Correct format for a Mayday call is:

- "Mayday, Mayday, Mayday." The call is always given three times in a row to keep it from being mistaken for a similar-sounding phrase, or to distinguish an actual distress signal from a message about a mayday call.

- "This is ____." The vessel name is repeated three times, followed by call sign if available.

- "Mayday. [vessel name]."

- "My position is ____." Position is given in latitude-longitude coordinates, or bearing and distance from a fixed point.

- "I am _____." The type of emergency, e.g. fire or sinking.

- "I require immediate assistance."

- "I have _____." The number of people on board and their condition, as well as any other pertinent information, e.g. abandoning to life rafts.

- "Over."

Some radio instructors suggest the mnemonic MIPDANIO for learning mayday signal format: Mayday, Identify, Position, Distress, Assistance, Number of crew, Information, Over.

Phonetic or Spelling Alphabets

The problem: a lot of letters sound alike. If two people are talking to each other on the telephone or a two-way radio, an "N" might be misheard as an "M," or a "B" might be heard as a "D," "T," or "C." If one person tells the other that the secret code that must be entered to save the world from imminent disaster is "M-A-T-T", there's a chance that we might all die because a little bit of static could cause the code to be heard as "N-8-B-D."

The solution: a phonetic alphabet or spelling alphabet, where code words are assigned to the letters of the alphabet acrophonically (that is, the code word assigned to a given letter starts with that letter, like Alpha for "A"). Using the Joint Army/Navy Phonetic Alphabet mentioned earlier, the above code becomes "Mike-Able-Tare-Tare" which is a little harder to mishear.

Today, the most commonly used spelling alphabet is the International Radiotelephony Spelling Alphabet. The alphabet was developed by the International Air Transport Association (IATA) and International Civil Aviation Organization (ICAO) after World War II and later adopted by organizations like International Maritime Organization (IMO), the Federal Aviation Administration (FAA), the American Radio Relay League (ARRL), and the North Atlantic Treaty Organization (NATO) (whose use of the alphabet led to its global spread and use of the common name, NATO phonetic alphabet).

In addition to these (and other) organizations, the alphabet is used by the military and in civilian industries (retail, IT and airlines for instance). The alphabet in its current form is:

Big Questions
What Is Fair Trade?

What is fair trade?

Shannon Fisher:

Fair trade is a system of manufacturing and purchasing intended to:

1) level the economic playing field for underdeveloped nations; and

2) protect against human rights abuses in the Global South.

Fair trade farmers are guaranteed fair market prices for their crops, and farm workers are guaranteed a living wage, which means workers who farm fair trade products and ingredients are guaranteed to earn enough to support their families and comfortably live in their communities. There are rules against inhumane work practices. Fair trade farming organizations are monitored for a safe work environment, lack of discrimination, the freedom to organize, and strict adherence to child labor laws. Agrochemicals and GMOs are also forbidden. If these rules are not followed, a product will not receive fair trade certification.

The quality of life in many communities producing fair trade-certified goods is greatly improved. Sometimes, farming communities are given profit sharing from the companies that source their ingredients, and those profits go to improving the community as a whole—be it with a library, medical facilities, town infrastructure, or opening small businesses to support the residents. A major goal of fair trade is to help foster sustainable development around the globe. By helping farming communities in third-world countries, the economy of the entire region gets a boost.

This post originally appeared on Quora. Click here to view.

Big Questions
Why Are There No Snakes in Ireland?

Legend tells of St. Patrick using the power of his faith to drive all of Ireland’s snakes into the sea. It’s an impressive image, but there’s no way it could have happened.

There never were any snakes in Ireland, partly for the same reason that there are no snakes in Hawaii, Iceland, New Zealand, Greenland, or Antarctica: the Emerald Isle is, well, an island.

Eightofnine via Wikimedia Commons // Public Domain

Once upon a time, Ireland was connected to a larger landmass. But that time was an ice age that kept the land far too chilly for cold-blooded reptiles. As the ice age ended around 10,000 years ago, glaciers melted, pouring even more cold water into the now-impassable expanse between Ireland and its neighbors.

Other animals, like wild boars, lynx, and brown bears, managed to make it across—as did a single reptile: the common lizard. Snakes, however, missed their chance.

The country’s serpent-free reputation has, somewhat perversely, turned snake ownership into a status symbol. There have been numerous reports of large pet snakes escaping or being released. As of yet, no species has managed to take hold in the wild—a small miracle in itself.

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