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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 | - |
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Auditory Assistance Devices
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The FCC allows auditory assistance devices on an unlicensed basis in the bands 72-73, 74.6-74.8, and 75.2-76 MHz, under Part 15. These allow hard-of-hearing people to participate in events together with people with normal hearing in settings like classrooms, theaters, and houses of worship. A low-power radio transmitter sends sound to the user’s receiver, which amplifies the sound and delivers it to headphones without disturbing non-users in the room. The FCC has expanded eligibility beyond assistance to handicapped persons to include simultaneous language translation.
The following background information is from the FCC Report & Order (FCC 13-59):
Part 15 of the Commission's rules provides for the operation of low power radio frequency (RF) devices without an individual license from the Commission. A party seeking to market a Part 15 unlicensed device to the public must first comply with the Commission's equipment authorization procedures, which, inter alia, require a demonstration that the device complies with the Commission's rules. As a general condition of operation, Part 15 devices may not cause harmful interference to any authorized services and must accept any interference that may be received from them or other Part 15 devices. Common Part 15 devices include cordless telephones, Wi-Fi devices, automated utility meter reading equipment, and auditory assistance devices.
Part 15 auditory assistance devices transmit audio via RF signals to specialized receivers used by listeners to enhance the reception of speech. By minimizing the disproportionate effects of background noise and reverberation on speech perception by people with disabilities, these devices improve the quality of sound over that which would be received via a loudspeaker system. Under the Part 15 rules, an auditory assistance device is defined as "[a]n intentional radiator used to provide auditory assistance to a handicapped person or persons. Such a device may be used for auricular training in an educational institution, for auditory assistance at places of public gatherings, such as a church, theater, or auditorium, and to handicapped individuals, only, in other locations."
The 72-76 MHz bands (72-73 MHz, 74.6-74.8 MHz, and 75.2-76 MHz) in which Part 15 auditory assistance devices are permitted to operate are allocated on a primary basis to licensed stations in the Public Mobile Service (Part 22), the Maritime Service (Part 80), the Aviation Service (Part 87), the Private Land Mobile Radio Service (Part 90), and the Radio Control (R/C) Radio Service (Part 95). In the bands adjacent to those bands in which Part 15 auditory assistance devices operate, the 73-74.6 MHz band is allocated on a primary basis to the Radio Astronomy Service for Federal and non-Federal use; the 74.8-75.2 MHz band is allocated on a primary basis to the Aeronautical Radionavigation Service for Federal and non-Federal use and is available for licensed use in the Radiodetermination Service (Part 87); and the 54-72 MHz (VHF TV channels 2-4) and 76-88 MHz bands (VHF TV channels 5 and 6) are allocated to the Broadcasting Service on a primary basis and are available for licensed TV broadcasting stations (Part 73).
On September 9, 2011, the Commission adopted an Order and Notice of Proposed Rulemaking (Auditory Assistance Device NPRM) in this proceeding that proposed to modify the Part 15 definition of "auditory assistance device" to expand the permissible uses of these devices to include simultaneous language interpretation. The expanded definition would allow Part 15 auditory assistance devices to be used by any person requiring simultaneous language interpretation at any location, in the same manner as permitted under Part 95 for Low Power Radio Service stations that operate in the 216-217 MHz band. The Commission took this action in response to a petition for declaratory ruling filed by Williams Sound Corporation (Williams Sound), a provider of wireless auditory assistance devices.
In the Auditory Assistance Device NPRM, the Commission sought comment on the advantages and disadvantages and potential benefits of expanding the permissible uses of Part 15 auditory assistance devices and any qualitative or quantitative costs associated with this proposal. It also sought comment on whether increased use of Part 15 auditory assistance devices for simultaneous language interpretation would increase the potential for harmful interference to authorized services in the 72-76 MHz and adjacent bands and whether additional safeguards or changes to the technical requirements for these devices would be necessary to prevent harmful interference to those services. In addition, the Commission sought comment on whether a more restrictive limit for Part 15 auditory assistance devices' out-of-band emissions is needed to prevent harmful interference to authorized services in the 72-76 MHz and adjacent bands and improve the reception of VHF TV channels 2-6.
Part 15 auditory assistance devices may operate in a full duplex mode of operation using necessary bandwidths up to 200 kilohertz wide. All fundamental emissions must be contained wholly within the 72-73 MHz, 74.6-74.8 MHz, and 75.2-76 MHz bands with a maximum field strength of 80 millivolts per meter (mV/m) measured at a distance of 3 meters, which is equivalent to a maximum effective radiated power (ERP) of 1.2 milliwatts (mW). The field strength of any unwanted emissions must not exceed 1,500 microvolts per meter (µV/m) measured at a distance of 3 meters, which is equivalent to an ERP of 0.4 microwatts (µW). The Commission asked what out-of-band emissions limit would be appropriate-the Section 15.209 limit, the unlicensed TV bands device limit, or some other limit – what would be an appropriate transition period for compliance, and whether currently approved Part 15 auditory assistance devices should be grandfathered for a limited time or permanently.
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Frequency Bands |
| Band | Use | Service | Table |
| 72 - 73 MHz | Auditory Assistance Devices (Part 15) | - | - |
| 74.6 - 74.8 MHz | Auditory Assistance Devices (Part 15) | - | - |
| 75.2 - 76 MHz | Auditory Assistance Devices (Part 15) | - | - |
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Access Broadband over Power Line (Access BPL)
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According to the FCC's definition, Access BPL is "a carrier current system installed and operated on an electric utility service as an unintentional radiator that sends radio frequency energy on frequencies between 1.705 MHz and 80 MHz over medium voltage lines or over low voltage lines to provide broadband communications and is located on the supply side of the utility service’s points of interconnection with customer premises. Access BPL does not include power line carrier systems as defined in § 15.3(t) or In-House BPL as defined in § 15.3(gg)."
Low voltage lines are defined as lines carrying, for example, 240/120 volts from a distribution transformer to a customer's premises. Medium voltage lines carry between 1,000 and 40,000 volts from a power substation to neighborhoods, and may be overhead or underground.
Access BPL is an unlicensed service operated under Subpart G of Part 15 of the FCC's rules. Radiated emission limits from medium voltage lines in the 1.705-30 MHz range must not exceed the limits in 47 CFR 15.209, and those from 30-80 MHz must not exceed the limits in 15.109(b). Systems that operate on low voltage lines must comply with 15.109(a) limits across the entire 1.705-80 MHz range.
When Access BPL systems must use notch filters to protect licensed services, the notch must be at least 25 dB below applicable Part 15 limits in the 1.705-30 MHz band, and at least 10 dB below the limits in the 30-80 MHz band.
There are 12 sub-bands in which Access BPL systems are not allowed to operate anywhere to protect aeronautical (land) stations and aircraft receivers. Those excluded bands are listed in 15.615(f), and are excluded in the list of Access BPL bands in this entry.
Access BPL systems are not allowed to operate within the sub-band 2173.5-2190.5 kHz within 1 km of coast station facilities listed in 47 CFR 15.615(f)(2)(i), to protect the internationally-recognized standard maritime calling frequency of 2182 kHz.
No Access BPL emissions are allowed in the 73.0-74.6 MHz radio astronomy band on overhead medium voltage lines within 65 km of the Very Large Array radio telescope in New Mexico (34 04 43.5N, 107 37 03.82W), or within 47 km of the VLA on underground power lines or overhead low voltage lines.
Access BPL operators must consult at least 30 days in advance when deploying systems near various FCC field offices, aeronautical and maritime stations, radar systems, radio astronomy stations, and research areas. Details are in 47 CFR 15.615(f)(3).
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