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Radio Astronomy (25.55 - 25.67 MHz)
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The band 25.55 - 25.67 MHz is allocated to the radio astronomy service. It is allocated on a primary exclusive basis in the U.S. and in all three ITU regions.
One radio astronomy facility that is being designed to make use of frequencies in this range is the Long Wavelength Array (LWA), which is co-located with the Very Large Array near Socorro, NM. The LWA design range is 10-88 MHz, with the main science goals and observing targets being relativistic particles in space (including supernova remnants, radio galaxies, and cosmic rays); cosmic evolution and the high-redshift universe; plasma astrophysics and space science; and transient cosmic radio sources.
Two major factors make radio astronomy at this low frequency very difficult. First, under normal conditions, the ionosphere heavily absorbs radio signals in this frequency range. Radio signals that are not absorbed will suffer strong and time-variable distortions due to density fluctations and motion of ionized material in the ionosphere.
Second, due to long-distance propagation of terrestrial radio signals in this range, radio frequency interference is a substantial problem, even for radio telescopes that are located at very remote sites. Within all three ITU regions, the band is allocated on an exclusive basis to radio astronomy, but individual countries can and do make allocations that do not conform with the ITU allocations.
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Frequency Bands |
| Band | Use | Service | Table |
| 25550 - 25670 kHz | Radio Astronomy (25.55 - 25.67 MHz) | Radio Astronomy | - |
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Shortwave Broadcasting
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Various bands throughout the HF (and, technically, the MF) spectrum are used for what is commonly referred to as shortwave broadcasting. Most broadcasts use AM modulation, which can be received on inexpensive shortwave receivers. Within these bands, shortwave broadcasters use channels spaced every 5 kHz. Different broadcasters may use the same channel at different times, and schedules of shortwave broadcasts (which are coordinated through the International Telecommunication Union) change on a regular basis. Most shortwave broadcasts also use very high power, as much as 500,000 W, using very large antenna arrays.
Because many broadcasts are sent through relay stations, the identity of the broadcaster does not necessarily tell you where the signal is coming from. For example, Radio Moscow is retransmitted from a relay station in Cuba, to provide a strong signal into North, Central, and South America.
Most shortwave bands are referred to by their approximate wavelength. For example, the 9400-9900 kHz band is referred to as the "31 meter band," because the wavelength is approximately 31 m.
The Website Short-Wave.info (linked below) can be used to identify shortwave stations broadcasting on specific frequencies at specific times, in a specified language.
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Frequency Bands |
| Band | Use | Service | Table |
| 2300 - 2495 kHz | 120 m tropical (regional) band | Broadcasting | - |
| 3200 - 3400 kHz | 90 m tropical band | Broadcasting | - |
| 3900 - 4000 kHz | 75 m band (shared with North American 80 m amateur radio band) | Broadcasting | - |
| 4750 - 5060 kHz | 60 m band | Broadcasting | - |
| 5900 - 6200 kHz | 49 m band | Broadcasting | - |
| 7200 - 7450 kHz | 41 m band (shared with amateur radio 40 m band) | Broadcasting | - |
| 9400 - 9900 kHz | 31 m band (most heavily used shortwave broadcasting band) | Broadcasting | - |
| 11600 - 12100 kHz | 25 m band | Broadcasting | - |
| 13570 - 13870 kHz | 22 m band (heavily used in Europe/Asia) | Broadcasting | - |
| 15100 - 15800 kHz | 19 m band | Broadcasting | - |
| 17480 - 17900 kHz | 16 m band | Broadcasting | - |
| 18900 - 19020 kHz | 15 m band (lightly used) | Broadcasting | - |
| 21450 - 21850 kHz | 13 m band | Broadcasting | - |
| 25600 - 26100 kHz | 11 m band (may be used for local digital shortwave broadcasting) | Broadcasting | - |
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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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