Radio Frequency Reference for Emergency Use

Emergency radio frequencies are allocated internationally across VLF (Very Low Frequency: 3–30 kHz), HF (High Frequency: 3–30 MHz), VHF (Very High Frequency: 30–300 MHz), and UHF (Ultra High Frequency: 300 MHz–3 GHz) bands. Different frequencies serve different purposes: maritime VHF for ships, HF for long-distance communication, UHF for terrestrial mobile networks. Licensing varies by country—amateur radio requires certification, marine/aviation frequencies are restricted, and some civilian bands (CB, GMRS, MURS) operate on license-free or licensed channels. Know your region's regulations before transmitting; unauthorized use can result in fines or equipment confiscation, and interference with distress frequencies endangers lives.

Transmitting on distress frequencies without genuine emergency is illegal in all countries. Do not test or practice on active emergency frequencies.

121.5 MHz (AM modulation) is the international aeronautical distress frequency monitored by all aircraft and emergency services worldwide. 156.8 MHz (Channel 16 VHF-FM) is the international maritime distress frequency monitored by coast guards and ships 24/7. Transmit MAYDAY (voice emergency) or SOS (Morse code: three dots, three dashes, three dots) followed by your location, nature of emergency, and number of people affected. Keep transmissions brief and clear: "MAYDAY MAYDAY MAYDAY, this is [vessel/aircraft name], position [latitude/longitude], [emergency description], requesting immediate assistance." Use these frequencies only for life-threatening emergencies; after establishing contact, responders will direct you to a working frequency to free these critical channels.

After distress contact is established, you will be directed to another frequency. Do not monopolize 121.5 or 156.8 MHz unless actively in distress.

Channel 16 (156.8 MHz) is monitored continuously; use Channels 68, 69, 70, 72, and 78A as secondary frequencies once contact is made. Single Sideband (SSB) frequencies for long-distance marine communication are 2.182 MHz (distress), 4.125 MHz, 6.215 MHz, 8.291 MHz, 12.290 MHz, and 16.420 MHz. Digital Selective Calling (DSC) on 2.187.5 MHz (HF) and 156.525 MHz (VHF) automates distress alerts. Know your vessel's primary radio system: HF/SSB for ocean-going vessels (range: 1,000+ nautical miles), VHF for coastal/near-shore (range: 20–60 nautical miles depending on antenna height). Activate DSC manually with vessel call sign and position before transmitting voice distress.

VHF range decreases dramatically below 30 feet above water; expect reduced range in valleys, canyons, or dense forests.

121.5 MHz is monitored by civilian and military aircraft, air traffic control, and emergency services worldwide. Use it for in-flight emergencies: engine failure, cabin depressurization, medical emergency, or aircraft damage. Transmit squawk code 7700 on your transponder simultaneously (alerts air traffic radar). If 121.5 MHz is congested, alternate frequencies include 123.45 MHz (U.S. search and rescue), 118.0–118.1 MHz (U.S. guard frequencies), and 243.0 MHz (military). Announce MAYDAY three times, aircraft type, tail number, position (latitude/longitude or landmarks), altitude, nature of emergency, number of people on board, and fuel time remaining: "MAYDAY MAYDAY MAYDAY, Cessna N12345, 40 miles east of Denver, 5,000 feet, engine failure, three persons on board, 20 minutes fuel."

Do not transmit false squawk codes or distress calls. Misuse diverts rescue resources and risks others' lives.

NOAA broadcasts continuous weather and hazard information on seven VHF frequencies: 162.550 MHz (most common), 162.400, 162.475, 162.425, 162.450, 162.500, and 162.525 MHz. These frequencies operate in the 162–164 MHz band with FM modulation and 100% digital, 24/7 transmission. Coverage varies by location and antenna height; obtain a NOAA Weather Radio receiver (portable or home-based) to access warnings before cell networks fail. Enable Specific Area Message Encoding (SAME) alerts to receive warnings for your county or region—receiver will sound alarm for tornado, flood, extreme wind, winter storm, or emergency alert system (EAS) announcements. Receiver cost ranges from $25–$100 USD; no license required to receive.

NOAA frequencies are receive-only; do not transmit on these frequencies.

Amateur (ham) radio provides decentralized communication independent of infrastructure. 80-meter band (3.5–4.0 MHz HF) reaches across continents; 40-meter band (7.0–7.3 MHz) is reliable day and night; 20-meter band (14.0–14.35 MHz) bridges intercontinental distances. VHF 2-meter band (144–148 MHz) and UHF 70-centimeter band (420–450 MHz) use local repeaters with coverage radius of 5–50 miles. International emergency calling frequency: 14.300 MHz (HF), 146.52 MHz (2-meter simplex, U.S.). Repeater offsets: 2-meter uplink frequency + 0.6 MHz = downlink (example: transmit 146.64 MHz, receive 147.24 MHz). Requires FCC license (Technician, General, or Extra class); study guides available free online. In prolonged grid-down scenarios, ham radio operators self-organize into emergency networks.

Ham radio requires FCC licensing in the U.S. Unlicensed transmission on ham frequencies is illegal and subject to fines.

Citizens Band (CB) Radio operates on 27 MHz with 40 channels; Channel 9 is the emergency channel monitored by truckers and emergency volunteers (no license required, 4-watt limit). General Mobile Radio Service (GMRS) uses 462–467 MHz with 16 channels; Channel 1 (462.5625 MHz) is designated for emergencies (FCC license required: $85 USD for 10 years). Multi-Use Radio Service (MURS) offers five license-free VHF channels (151.820, 151.880, 151.940, 154.280, 154.330 MHz) with 2-watt limit for personal emergencies. CB radios are cheapest ($30–$150 USD, no license), GMRS mid-range ($100–$400 USD, licensed), MURS affordable and portable ($50–$200 USD). CB reach: 5–20 miles depending on terrain and antenna; GMRS/MURS: 10–30 miles with elevation advantage.

Exceeding power limits, antenna height, or transmitting outside assigned frequencies violates FCC regulations.

Activate your radio and listen first—never interrupt active distress communications. Speak slowly and clearly at normal volume; shouting distorts audio. Keep transmissions under 30 seconds to allow responses. Use simple language: avoid jargon unless speaking to ham operators or mariners. Phonetic alphabet aids clarity—spell your name: Alfa, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel. Always announce your position using latitude/longitude (degrees/minutes format), named landmarks, or distance from known location. Repeat critical information twice: "My position is 40 degrees 43 minutes North, 104 degrees 59 minutes West, repeat, 40–43 North, 104–59 West." Turn off non-critical radios to preserve batteries; many survival radios support solar charging and hand-crank generators. Monitor your assigned frequency continuously—do not rely on radios to alert you of incoming transmissions if batteries are depleted.

Battery failure is common in emergencies. Carry spare batteries, hand-crank backup radio, or solar-powered receiver.