The Toolbox — Frequencies

Emergency & SAR

COSPAS-SARSAT, EPIRB, ELT, PLB, AIS, GPS/GNSS, INMARSAT, rescue helicopter, and SAR coordination frequencies.

COSPAS-SARSAT System

International satellite system for detection of emergency distress signals. EPIRB, ELT, and PLB devices all transmit on 406 MHz to COSPAS-SARSAT satellites.

Frequency	System	Notes
406.028 MHz	COSPAS-SARSAT uplink	Primary distress frequency — EPIRB, ELT, and PLB transmit here
121.500 MHz	Homing / legacy alert	All EPIRB/ELT/PLB also transmit on 121.5 for final homing by SAR aircraft
243.000 MHz	Military homing	Military aircraft home on 243.0 MHz — dual-frequency beacons include this
1544.5 MHz	LEOSAR downlink (L-band)	Satellites relay distress signals to ground stations on this frequency
1544.1 MHz	MEOSAR downlink (L-band)	Medium-orbit GNSS satellites relay 406 MHz alerts — near-real-time detection and independent position
406 MHz (via GEO)	GEOSAR	Geostationary satellites relay 406 MHz alerts almost instantly, but can't fix position without encoded GPS

EPIRB (Marine)

Type	Frequency	Power	Notes
406 MHz EPIRB	406.028 MHz + 121.5 MHz	5W minimum (406 MHz)	Category I — automatically releases and activates in water. Category II — manual activation.
SART (Search and Rescue Transponder)	9 GHz (X-band radar)	400 mW minimum	Responds to X-band radar interrogation — creates line of 12 dots on radar screen
AIS-SART	161.975 / 162.025 MHz (AIS)	1W	Broadcasts AIS signal visible on AIS-equipped vessels — shows position, not radar dots
EPIRB registration	N/A	N/A	All 406 MHz EPIRBs must be registered with NOAA — includes vessel MMSI and owner contact

ELT (Aviation)

Type	Frequency	Activation	Notes
406 MHz ELT	406.028 MHz + 121.5 MHz	Impact (G-switch) or manual	Most US civil aircraft must carry an ELT (14 CFR 91.207); a 121.5 MHz ELT still meets the rule, but 406 MHz is strongly recommended. Register with NOAA.
ELT homing	121.500 MHz	Continuous after activation	SAR aircraft and Civil Air Patrol use 121.5 for final homing to crash site
ELT test procedure	121.500 MHz (briefly)	First 5 min of each hour only	Self-test only — maximum 3 audio sweeps. Notify ATC if accidental activation.
ELT battery replacement	N/A	N/A	Replace battery after any activation and per manufacturer's time-based schedule

PLB (Personal Locator Beacon)

PLBs are for personal use on land. Unlike EPIRBs they are not designed for automatic water activation. Must be manually activated in an emergency.

Type	Frequency	Power	Notes
Personal Locator Beacon (PLB)	406.028 MHz + 121.5 MHz	5W (406 MHz)	Land-based personal distress beacon. Not designed for water immersion (unlike EPIRB).
PLB registration	N/A	N/A	Must be registered with NOAA at beaconregistration.noaa.gov — free registration
PLB battery life	N/A	N/A	Minimum 24 hours continuous operation at −20°C per COSPAS-SARSAT specifications
GPS-equipped PLB	406 MHz + GPS L1 (1575.42 MHz)	5W	Position included in distress signal — dramatically reduces SAR response time

AIS Frequencies

Channel	Frequency	Notes
AIS Channel 1 (87B)	161.975 MHz	AIS Class A and B transponders transmit and receive
AIS Channel 2 (88B)	162.025 MHz	AIS Class A and B transponders transmit and receive
AIS safety messages	161.975 / 162.025 MHz	Safety-related text messages broadcast on AIS channels
Long-range AIS (Ch 75/76)	156.775 / 156.825 MHz	Low-rate AIS messages intended for reception by satellite

GPS & GNSS Frequencies

System	Frequency	Notes
GPS L1	1575.42 MHz	Primary civilian GPS signal — C/A code
GPS L2	1227.60 MHz	Secondary GPS — precision (P) code, dual-frequency receivers
GPS L5	1176.45 MHz	Third GPS signal — safety-of-life applications, aviation
GLONASS L1	1598.0625–1609.3125 MHz	Russian GNSS — FDMA system, slightly different from GPS
Galileo E1	1575.420 MHz	European GNSS — shares frequency with GPS L1
BeiDou B1	1561.098 MHz	Chinese GNSS — B1I signal
SBAS (WAAS/EGNOS)	1575.42 MHz	Satellite-based augmentation — WAAS in US, EGNOS in Europe
DGPS (MF beacon)	285–325 kHz	MF differential corrections — the US Coast Guard network was shut down in 2020

INMARSAT & Satellite Communications

System	Frequency	Notes
INMARSAT-C	1.5–1.6 GHz (L-band)	Store-and-forward messaging — most widely used maritime GMDSS system
INMARSAT Fleet 77	L-band (1.5–1.6 GHz)	Voice, data, and fax for maritime — now retired
INMARSAT Fleet Broadband	L-band	High-speed data — up to 432 kbps
INMARSAT BGAN	L-band	Broadband Global Area Network — portable satellite internet
INMARSAT coverage	N/A	Geostationary — covers approximately 76°N to 76°S latitude
Iridium	1616–1626.5 MHz (L-band)	LEO constellation — true polar coverage including Arctic and Antarctic
Globalstar	2483.5–2500 MHz (S-band downlink)	LEO constellation — voice and data

SAR On-Scene Coordination Frequencies

Frequency	Use	Notes
121.500 MHz	Aeronautical emergency (VHF)	Monitored by ATC, FSS and many aircraft
243.000 MHz	Military SAR coordination (UHF)	Military aircraft and some USCG helicopters
123.100 MHz	SAR auxiliary (aviation)	Secondary SAR coordination frequency for aviation
156.800 MHz (Ch 16)	Maritime SAR coordination (VHF)	Primary maritime distress and SAR coordination channel
2.182 MHz	MF maritime distress (voice)	International MF distress — the USCG ended its 2182 kHz watch in 2013
3.023 MHz	Maritime/aviation SAR coordination (HF)	International aeronautical SAR frequency
5.680 MHz	Maritime/aviation SAR coordination (HF)	International SAR on-scene coordination
8.364 MHz	Aeronautical HF distress	International aeronautical distress frequency (HF)

Rescue Helicopter & Civil Air Patrol Frequencies

Frequency	Use	Notes
121.500 MHz	Primary SAR homing and on-scene	Guard frequency — monitored by all SAR helicopters
123.100 MHz	SAR auxiliary	Secondary coordination with SAR aircraft
156.800 MHz	Maritime SAR coordination	VHF Channel 16 — used by USCG helicopters working with vessels
282.800 MHz	Military SAR (UHF)	Common US military helicopter frequency
148–150 MHz (VHF-FM)	Civil Air Patrol	CAP uses assigned federal VHF-FM channels in this band