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Instrument Landing System
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Pilots use various radio aids to help guide them to the runway for landing, particularly in poor weather or other low-visibility conditions. Collectively, these aids are referred to as the Instrument Landing System (ILS). ILS utilizes 75 MHz, 108.1-111.95 MHz, and 329.15-335.0 MHz. According to NTIA, "there is international agreement within the International Civil Aviation Organization (ICAO) establishing the ILS as a standard landing system, and the ILS is used extensively worldwide."
Localizer
The localizer helps establish the proper horizontal path for an approach to the runway. The localizer transmission consists of two signals, one modulated with a 90 Hz tone and transmitted with a beam pointed along the left side of the approach, and another modulated with a 150 Hz tone and transmitted with a beam pointed along the right side of the approach. The plane's ILS receiver compares the strength of the two modulated tones and can determine whether the plane is aligned too far left (too much 90 Hz tone), too far right (too much 150 Hz tone), or along the center of the runway (equal strengths for both tones).
The localizer signal is useful for a distance of approximately 18 nm from the runway.
The localizer and glide slope frequencies are paired, so that the pilot need only select one, and the other is set automatically. The localizer channels are in the 108.1-111.95 MHz band. Note that the localizer channels are interspersed with channels for VHF Omnidirectional Range (VOR) signals in this band. VORs are used for enroute navigation, as opposed to precision navigation to the runway. See the related links for a full list of the ILS channel plan.
Glide Slope
The glide slope indicator works similarly to the localizer signal, but instead of indicating proper horizontal position, it indicates the proper vertical path to the runway (typically a 3 deg slope down to the runway). The 90 Hz tone is transmitted pointed above the proper path, while the 150 Hz modulated signal is pointed below the proper path. Comparison of the strength of the two tones informs the ILS receiver (and pilot) whether the plane is on the correct vertical path.
The glide slope signal is useful out to a distance of about 10 nm from the runway.
The glide slope and localizer frequencies are paired, so that the pilot need only select one, and the other is set automatically. The glide slope channels are in the 329.15-335.0 MHz band.
See the related links for a full list of the ILS channel plan.
Marker Beacons
The Instrument Landing System (ILS) marker beacons are located at varying distances along the approach to a runway to indicate the approximate distance to the runway. Marker beacons are typically used when an airport does not have Distance Measurement Equipment (DME) capabilities.
Outer markers are located between about 4-7 miles from the end of the runway. The antenna system, typically two yagis in a V configuration with the open part of the V pointing upwards, creates a narrow vertical beam that the pilots receive when they fly over. The outer marker transmits an AM signal at 75 MHz with a 400 Hz modulated tone.
The middle marker is typically about 2000 ft from the end of the runway, and transmits a 1 kHz modulated tone. The middle marker beacon is often a simple three-element yagi pointed straight up.
The inner marker is typically 700-800 ft from the end of the runway and transmits a 3 kHz modulated tone.
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Frequencies |
| Frequency | Bandwidth | Use | Service | Table |
| 75 MHz | 400 kHz | Instrument Landing System outer, middle, and inner markers | Aeronautical Radionavigation | - |
Frequency Bands |
| Band | Use | Service | Table |
| 108.1 - 111.95 MHz | Instrument Landing Systemn localizer signal | Aeronautical Radionavigation | - |
| 329.15 - 335 MHz | Instrument Landing System glide slope signal | Aeronautical Radionavigation | - |
External Links:
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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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IEEE 802.15.4 HRP UWB
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High pulse repetition frequency ultra-wideband (HPR UWB) is one of the physical layers defined for low data rate personal area network (LR-WPAN) communications in the IEEE 802.15.4 standard.
According to the FiRa Consortium:
"In challenging environments, such as parking structures, hospitals, airports and high density venues, ultra-wideband (UWB) technology outperforms other technologies in terms of accuracy, power consumption, robustness in wireless connectivity, and security, by a wide margin.
"UWB securely determines the relative position of peer devices with a very high degree of accuracy and can operate with line of sight at up to 200 meters. In contrast to narrow band wireless technologies, the use of wide bandwidth means UWB provides very stable connectivity, with little to no interference and offers highly precise positioning, even in congested multi-path signal environments.
"By calculating precise location, fine ranging based on UWB is a more secure approach to closing and opening locks, whether those locks are installed on a car door, a warehouse entryway, a conference room, or your front door."
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Frequencies |
| Frequency | Bandwidth | Use | Service | Table |
| 499.2 MHz | 499.2 MHz | 802.15.4 HRP UWB Channel 0 | - | - |
| 3494.4 MHz | 499.2 MHz | 802.15.4 HRP UWB Channel 1 | - | - |
| 3993.6 MHz | 499.2 MHz | 802.15.4 HRP UWB Channel 2 | - | - |
| 3993.6 MHz | 1.3312 GHz | 802.15.4 HRP UWB Channel 4 | - | - |
| 4492.8 MHz | 499.2 MHz | 802.15.4 HRP UWB Channel 3 | - | - |
| 6489.6 MHz | 1.0816 GHz | 802.15.4 HRP UWB Channel 7 | - | - |
| 6489.6 MHz | 499.2 MHz | 802.15.4 HRP UWB Channel 5 | - | - |
| 6988.8 MHz | 499.2 MHz | 802.15.4 HRP UWB Channel 6 | - | - |
| 7488 MHz | 499.2 MHz | 802.15.4 HRP UWB Channel 8 | - | - |
| 7987.2 MHz | 1.3312 GHz | 802.15.4 HRP UWB Channel 11 | - | - |
| 7987.2 MHz | 499.2 MHz | 802.15.4 HRP UWB Channel 9 | - | - |
| 8486.4 MHz | 499.2 MHz | 802.15.4 HRP UWB Channel 10 | - | - |
| 8985.6 MHz | 499.2 MHz | 802.15.4 HRP UWB Channel 12 | - | - |
| 9484.8 MHz | 1.35497 GHz | 802.15.4 HRP UWB Channel 15 | - | - |
| 9484.8 MHz | 499.2 MHz | 802.15.4 HRP UWB Channel 13 | - | - |
| 9984 MHz | 499.2 MHz | 802.15.4 HRP UWB Channel 14 | - | - |
External Links:
Associated Files:
802.15.4 HRP UWB PHY band allocation
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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 |
External Links:
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