science

International distress frequency

International distress frequency is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand International distress frequency rather than just read about it. In short: An international distress frequency is a radio frequency that is designated for emergency communication by international agreement. History For much of the 20th century, 500 kHz was the primary international distress frequency.

Key takeaways

International distress frequency belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect International distress frequency to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of International distress frequency from memory before moving on to harder problems.

Reference excerpt

An international distress frequency is a radio frequency that is designated for emergency communication by international agreement.

History For much of the 20th century, 500 kHz was the primary international distress frequency. Its use has been phased out in favor of the Global Maritime Distress and Safety System (GMDSS). Use of some distress frequencies is permitted for calling other stations to establish contact, whereupon the stations move to another frequency. Such channels are known as distress, safety and calling frequencies. Satellite processing from all 121.5 or 243 MHz locators has been discontinued. Since February 1, 2009, the U.S. Coast Guard only monitors distress signals from emergency position indicating radio beacons (EPIRBs) that broadcast using digital 406 MHz signals. Digital 406 MHz models became the only ones approved for use in both commercial and recreational watercraft worldwide on January 1, 2007.

Maritime Mobile Service frequencies International distress frequencies, currently in use are:

2182 kHz for medium range maritime voice use. The United States Coast Guard stated "beginning August 1, 2013 the Coast Guard would no longer monitor 2182 kHz". Many other MRCCs, for example most in northern Europe, now only have MF capabilities and no HF. Several HF maritime voice frequencies exist for long-distance distress calls: 4125 kHz 6215 kHz 8291 kHz 12290 kHz 16420 kHz Marine VHF radio Channel 16 (156.8 MHz) for short range maritime use 406 MHz to 406.1 MHz is used by the Cospas-Sarsat international satellite-based search and rescue (SAR) distress alert detection and information distribution system

Digital selective calling frequencies Several maritime frequencies are used for digital selective calling (DSC), and they are also monitored for DSC distress signals:

2.1875 MHz 4.2075 MHz 6.312 MHz 8.4145 MHz 12.577 MHz 16.8045 MHz 156.525 MHz, Marine VHF radio Channel 70

Aeronautical frequencies 121.5 MHz is the civilian aircraft emergency frequency or International Air Distress frequency. It is used by some civilian emergency locator beacons; however, the Cospas-Sarsat system no longer monitors the frequency. 243 MHz for NATO military aircraft emergency frequencies 406 MHz to 406.1 MHz is used by the Cospas-Sarsat international satellite-based search and rescue (SAR) distress alert detection and information distribution system

Search And Rescue frequencies 123.1 MHz – Aeronautical Auxiliary Frequency (International voice for coordinated SAR operations). 138.78 MHz – U.S. military voice SAR on-the-scene use. This frequency is also used for direction finding (DF). 155.160 MHz 172.5 MHz – U.S. Navy emergency sonobuoy communications and homing use. This frequency is monitored by all U.S. Navy ASW aircraft assigned to a SAR mission. 282.8 MHz – Joint/combined on-the-scene voice and DF frequency used throughout NATO 406 MHz / 406.1 MHz – Cospas-Sarsat international satellite-based search and rescue (SAR) distress alert detection and information distribution system Emergency position-indicating radiobeacon station (EPIRB) Search and rescue transponder (SART) Survival radio

Amateur radio frequencies

VHF, UHF calling frequencies can also be used to make emergency calls

MF and HF frequencies Emergency Centre of Activity (ECOA) frequencies informally established by the International Amateur Radio Union regional organizations:

Emergency/Disaster Relief Interoperation Voice Channels of the amateur radio Global ALE High Frequency Network: 3791.0 kHz USB 7185.5 kHz USB 10145.5 kHz USB 14346.0 kHz USB 18117.5 kHz USB 21432.5 kHz USB 24932.0 kHz USB 28312.5 kHz USB

Other frequencies Citizens band (CB) radio (not available in all countries) Emergency channels 9 (27.065 MHz AM) and 19 (27.185 MHz AM) GMRS: 462.675 MHz is a UHF mobile distress and road information calling frequency allocated to the General Mobile Radio Service and used throughout Alaska and Canada for emergency communications; sometimes referred to as "Orange Dot" by some transceiver manufacturers who associated a frequency with a color-code for ease of channel coordination, until the creation of the Family Radio Service, in 1996, "GMRS 675" or Channel 6/20 on mobile radios today. Its bandwidth can vary between 12.5, 25 and 50 kHz, and is also allocated to Ch. 20 on 22-channel FRS/GMRS "blister pack" radios. It can have a repeater input frequency of 467.675 MHz, and a tone squelch of 141.3 Hz. After FCC deregulation of simplex FRS/GMRS radios, FRS users may transmit up to 2 watts on the GMRS emergency channel 20 (462.675 MHz) with 141.3 Hz CTCSS, or channel 20-22. MURS: 151.940 MHz (only available in the United States) FRS: FRS channel 1: 462.5625 MHz (carrier squelch, no tone or sub-channel), channel 3: 462.6125 MHz and channel 20: 462.6750 MHz (141.3 Hz CTCSS - channel 20, code 22 or channel 20-22). UHF CB (Australia): Emergency channels 5/35 (476.525/477.275 MHz). Channel 5 is the designated simplex and repeater output emergency channel, while channel 35 is used as the repeater input frequency for duplex operation. UHF CB is only available in Australia and New Zealand. PMR446 (Europe): Channel 1 analog (446.00625 MHz, CTCSS 100.0 Hz, channel 1/12), Channel 8 analog (446.09375 MHz, CTCSS 123.0 Hz, channel 8/18). PMR446 (Europe): Mountain Rescue Channel 7 analog (446.08125 MHz), CTCSS 85.4 Hz (Channel 7/7 in most radios, not all) CB245 (Thailand): VHF Citizen Band Channel 1 (245.0000 MHz) and Channel 41 (245.5000 MHz) CB78 (Thailand): VHF-LOW Citizen Band Channel 41 (78.5000 MHz)

See also Aircraft emergency frequency Distress signal Global Maritime Distress Safety System Mayday SOS

References

Worked examples

Example 1 — a first encounter with International distress frequency

Start with the simplest possible case. Write down what International distress frequency claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to International distress frequency before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about International distress frequency ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of International distress frequency

In research: International distress frequency appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses International distress frequency in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: International distress frequency is common in secondary-school and first-year university syllabi. It links to neighbouring topics Distress signals, Emergency communication, International telecommunications, so understanding it makes those chapters shorter.
In everyday life: Look for International distress frequency outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study International distress frequency in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what International distress frequency means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain International distress frequency out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is International distress frequency in simple terms?

An international distress frequency is a radio frequency that is designated for emergency communication by international agreement. History For much of the 20th century, 500 kHz was the primary international distress frequency.

Why does International distress frequency matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study International distress frequency?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on International distress frequency.