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Emergency Position Indicating Radiobeacon (EPIRB); Emergency Locator Transmitter (ELT); Personal Locating Beacon (PLB)
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EPIRBs, ELTs, and PLBs are various forms of radiobeacons that are used to locate people in distress. Generally, the term EPIRB is used for maritime distress beacons, ELT refers to an aviation beacon; and PLB refers to beacons worn on individuals (for example, hikers).
The beacons normally remain silent, and are activated either manually or automatically (for example, when they detect water) in case of an emergency. Their beacon signal can then be picked up by a receiver, and used to locate the device.
The beacons operate on one or more of three worldwide frequencies: 121.5, 243, and 406 MHz. However, since Feb 1st, 2009, 121.5 and 243 MHz signals are no longer received by satellites, and can therefore be much harder (and take much longer) to locate. Newer 406 MHz beacons can be located by a variety of satellites, including the COSPAS-SARSAT system established by the U.S., Russia, Canada, and France. Some 406 MHz beacons have built-in GPS receivers, and can encode their latitude and longitude in their beacon transmission. With these types, even geostationary satellites, such as the GOES weather satellites, can relay an accurate location of the beacon to authorities.
The satellite receivers in the 406 MHz band have a bandwidth of 24 kHz. The 406 MHz beacons transmit their signals at a bit rate of 400 bps.
EPIRBs are a component of the International Maritime Organization's (IMO's) Global Maritime Distress and Safety System (GMDSS).
Galileo, the European radionavigation-satellite system, will incorporate receivers for the 406 MHz beacons, and may even be able to talk back. According to the European Space Agency, "Galileo is to play an important part of the Medium Earth Orbit Search and Rescue system (MEOSAR). Galileo satellites will be able to pick up signals from emergency beacons carried on ships, planes or persons and ultimately send these back to national rescue centres. From this, a rescue centre can know the precise location of an accident. At least one Galileo satellite will be in view of any point on Earth so near real-time distress alert is possible. In some cases, feedback could be sent back to a beacon, something which is only made possible by Galileo."
EPIRBs transmit a 0.5s burst every 50 seconds, according to the ITU. More information on the Cospas-Sarsat system is available in ITU-R Report SM.2258 (link below).
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Frequencies |
| Frequency | Bandwidth | Use | Service | Table |
| 121.5 MHz | 3 kHz | EPIRB/ELT/PLB (analog, older style, no longer tracked by satellites) | - | - |
| 243 MHz | 3 kHz | EPIRB/ELT/PLB (analog, older style, no longer tracked by satellites) | - | - |
Frequency Bands |
| Band | Use | Service | Table |
| 406 - 406.1 MHz | EPIRB/ELT/PLB (digital) | Mobile-satellite | - |
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Military Mobile-Satellite Communications (NTIA)
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Satellites operating in the mobile-satellite service in this band are used by the military services and the Coast Guard. The military mobile-satellite communications networks in the band serve ships at sea, aircraft, land-based forces, and a variety of other U.S. military fixed and mobile terminals used by mobile users. The bands 225-322 MHz and 335.4- 399.9 MHz are the only bands below 7250 MHz available for Federal Government mobile-satellite communications, and the narrowband satellite links are frequently the only reliable means of communications.
The military makes extensive use of the mobile-satellite service operating in this band because the electromagnetic waves can penetrate foliage, inclement weather, and urban terrain including concrete-reinforced buildings. Small antennas can be used at the earth terminals making it easy to transport the stations. There are numerous satellite earth terminals currently in use by the military, many of which are small and portable enough to be carried deep into theaters of operation.
The Federal use of the band for mobile satellites was initiated in 1978 with the Navy's Fleet Satellite Communications System (FLTSATCOM), a constellation of five geostationary satellites operating in the band 235-322 MHz, channelized into the downlinks at 243.855-269.95 MHz and corresponding uplinks in the band 292.85- 317.325 MHz. The Navy began upgrading the FLTSATCOM in the 1990s with the UHF Follow-On (UFO) satellites. The UFO satellites offer increased communications channel capacity over the same frequency spectrum used by the previous FLTSATCOM systems. Each UFO satellite has 39 channels with a total 555 kHz bandwidth. The satellite payload comprises 21 narrowband channels at 5 kHz each and 17 relay channels at 25 kHz.3 These channels are used by the military agencies for tactical communications on land, ships, submarines, and aircraft. The Coast Guard also uses channels on the military satellites on some of their ships.
The Department of Defense (DOD) Defense Satellite Communications System (DSCS-III) series of geostationary satellites operating in the 7- and 8- GHz bands also carry a transponder in this band called the single channel transponder (SCT) that provides communications for emergency action messages to the forces. The Military, Strategic, and Tactical Relay Satellite (MILSTAR) geostationary satellite also has mobile-satellite capability in this band, with a transponder that provides four Air Force Satellite Communications (AFSATCOM IIR) channels and a fleet broadcast channel.
The Navy has launched the next generation mobile satellites, termed the Multiple User Objective System (MUOS) that use the bands 243.525-270.05 MHz and 280-320 MHz. The MUOS is undergoing testing and is not fully operational as of September, 2014. The Navy has awarded contracts for the MUOS, and overall, the MUOS will be $6.4 billion system. The MUOS enables communications to various terminal devices such as handhelds, laptops, and personal communications units. To support legacy systems, the MUOS will use a narrowband system of 64 kbps/channel and below. The MUOS will use wideband-code-division-multiple-access (WCDMA) technology, the same technology as some forms of the third generation (3G) commercial cellphone technology. The capacity is 4 Mbps per antenna beam.
In general, the band 225-328.6 MHz is reserved for military uses by North Atlantic Treaty Organization (NATO), its member nations, and other U.S. allies. The band is harmonized among NATO-member nations for secure communications.
(Information extracted from the NTIA Federal Government Spectrum Use Reports, dated December 1, 2015)
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Frequency Bands |
| Band | Use | Service | Table |
| 225 - 322 MHz | Military mobile-satellite communications | Mobile-satellite | F |
| 335.4 - 399.9 MHz | Military mobile-satellite communications | Mobile-satellite | F |
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Military Aeronautical/ATC Communications and Telemetry (NTIA)
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The military agencies, National Guard units, the Coast Guard, and the FAA are the heaviest users of the band 225-328.6 MHz, using the band for critical air-to-ground-to-air communications systems. The military agencies and National Guard units use the band 225-328.6 MHz for various types of aeronautical communications, e.g., for training flights and air-traffic-control functions such as ground control, approach control, enroute aircraft separation, and in-flight refueling services. The Air Force, Army, Navy, and the FAA have thousands of frequency assignments for air-to-ground-to-air communications in the band 225-328.6 MHz. Most of these assignments are to ground stations.
The Coast Guard uses the band on its maritime search-and-rescue aircraft and other aircraft for air-to-ground-to-air communications. The military agencies, National Guard units, and the FAA make extensive use of the band 225-328.6 MHz which alleviates possible impact of the national airspace civilian air-to-ground-to-air communications operating in the bands within 117.975-137 MHz. Thus, the Federal use of the band 225-328.6 MHz for aeronautical communications plays an important part in national defense and security, and to control the nation's airspace.
The band 225-328.6 MHz is also used for essential communications by a number of other agencies such as NASA, DOE, and DOC. NASA uses the band for aircraft communications, and for International Space Station (ISS) communications during Extravehicular Activity (EVA); and DOC uses the band on National Oceanographic and Atmospheric Administration (NOAA) hurricane-hunter aircraft, and on ground stations to communicate with other hurricane-hunter aircraft.
The military agencies use the band 225-328.6 MHz for a major tactical communications system to provide anti-jam, secure, frequency-hopping radio communications for tactical air-to-air and air-to-ground-to-air communications. The uses include coordination and vectoring of aircraft to targets, and large scale training exercises.
For example, the major radio communications systems are deployed on all rotary wing aircraft, and are used by all operational aviation units, air traffic services, and units. The radio communications system enables interoperability communications among Air Force, Navy, Army, and NATO units.
The Navy makes extensive use of the band for aeronautical telemetry, and DOE also uses the band for this purpose. The Navy uses the band for flight testing of military aircraft. The military agencies also use this band for telemetry systems for rocket testing.
In generall, the band 225-328.6 MHz is reserved for military uses by North Atlantic Treaty Organization (NATO), its member nations, and other U.S. allies. The band is harmonized among NATO-member nations for secure communications.
(Information extracted from the NTIA Federal Government Spectrum Use Reports, dated December 1, 2015)
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Frequency Bands |
| Band | Use | Service | Table |
| 225 - 328.6 MHz | Military aeronautical communications and telemetry | Mobile | F |
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Federal Search and Rescue Communications on 243 MHz (NTIA)
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The footnotes 5.111, 5.199, and 5.256 were adopted by the International Telecommunication Union and are incorporated into the U.S. Table of Frequency Allocations. Among other things, these footnotes provide for the use of the 243 MHz frequency for search and rescue purposes.
The frequency 243 MHz is used on the radios onboard most Federal aircraft as a special channel, called a "guard" channel that is used for distress and safety purposes, including search and rescue. The 243 MHz channel is always activated on aircraft and ground systems even though another channel may be in use on a transceiver operating in the band. For example, a military aircraft in distress could make an emergency distress call for assistance on 243 MHz, and all other aircraft or ground stations in the area would hear it immediately and take action.
In general, the band 225-328.6 MHz is reserved for military uses by North Atlantic Treaty Organization (NATO), its member nations, and other U.S. allies. The band is harmonized among NATO-member nations for secure communications.
(Information extracted from the NTIA Federal Government Spectrum Use Reports, dated December 1, 2015)
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Frequencies |
| Frequency | Bandwidth | Use | Service | Table |
| 243 MHz | 25 kHz | Federal Search and Rescue | Mobile | F |
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Military Battle Simulation Systems (NTIA)
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The military agencies use the band for research, development, testing, and evaluation of various types of communications and sensing systems. The military agencies operate training center instrumentation systems in this band for data links connecting battle simulation systems on participants' platforms (airborne, shipborne, or surface) to central processing facilities.
In general, the band 225-328.6 MHz is reserved for military uses by North Atlantic Treaty Organization (NATO), its member nations, and other U.S. allies. The band is harmonized among NATO-member nations for secure communications.
(Information extracted from the NTIA Federal Government Spectrum Use Reports, dated December 1, 2015)
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Frequency Bands |
| Band | Use | Service | Table |
| 225 - 328.6 MHz | Military battle simulation systems | Mobile | F |
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