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Airport Surveillance Radar (ASR-11)
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According to the FAA:
Airport Surveillance Radar (ASR-11) is an integrated primary and secondary radar system that has been deployed at terminal air traffic control sites. It interfaces with both legacy and digital automation systems and provides six-level national weather service calibrated weather capability that provides enhanced situational awareness for both controllers and pilots.
The primary surveillance radar uses a continually rotating antenna mounted on a tower to transmit electromagnetic waves that reflect, or backscatter, from the surface of aircraft up to 60 nautical miles from the radar. The radar system measures the time required for radar to echo to return and the direction of the signal. From this, the system can then measure the distance of the aircraft from the radar antenna and the azimuth, or direction, of the aircraft in relation to the antenna. The primary radar also provides data on six levels of rainfall intensity and operates in the range of 2700 to 2900 MHz. The transmitter generates a peak effective power of 25 kW and an average power of 2.1 kW. The average power density of the ASR-11 signal decreases with distance from the antenna. At distances of more than 43 feet from the antenna, the power density of the ASR-11 signal falls below the maximum permissible exposure levels established by the Federal Communications Commission (FCC).
The secondary surveillance radar uses a second radar beacon antenna attached to the top of the primary radar antenna to transmit and receive area aircraft data for barometric altitude, identification code, and emergency conditions. Military, commercial, and some general aviation aircraft have transponders that automatically respond to a signal from the secondary radar by reporting an identification code and altitude. The air traffic control centers uses this system data to verify the location of aircraft within a 60-mile radius of the radar site. The secondary radar also provides rapid identification of aircraft in distress. The secondary radar operates in the range of 1030 to 1090 MHz. Transmitting power ranges from 160 to 1500 watts.
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Frequency Bands |
Band | Use | Service | Table |
1030 - 1090 MHz | Airport Surveillance Radar (ASR-11) secondary radar band | Aeronautical Radionavigation | F |
2700 - 2900 MHz | Airport Surveillance Radar (ASR-11) primary radar band | Aeronautical Radionavigation | F |
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Solar Flux Index (SFI)
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The flux density of radio emissions from the Sun has been measured at a frequency of 2800 MHz since approximatey 1950. This solar flux measurement is referred to as F10.7, because 2800 MHz corresponds to a wavelength of 10.7 cm. F10.7 is strongly correlated with the amount of UV radiation coming from the Sun, but can be measured on the ground, as opposed to UV measurements which must be measured from space, above the absorption of the Earth's atmosphere. Making accurate long-term ground-based radio measurements is more reliable and less costly than producing long-term space-based UV measurements.
The amount of solar UV energy, as traced by F10.7, is an important assessment of ionization in the Earth's ionosphere, which in turn has a major impact on radio communications on Earth. F10.7 can also be used to study solar storms, which can produce major disruptions to satellite systems and terrestrial power grids.
F10.7 has always been measured by Canadian radio astronomy stations. It is presently produced by the Dominion Radio Astrophysical Observatory (DRAO) near Penticton, British Columbia.
F10.7, also called the Solar Flux Index (SFI), is measured in a 100 MHz bandwidth from 2750-2850 MHz. It is in units of 10^-22 W/m^2/Hz.
A good article on measurement of the Solar Flux Index appeared in the February 2013 issue of QST magazine.
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Frequency Bands |
Band | Use | Service | Table |
2750 - 2850 MHz | Solar Flux Index (SFI) | Radio Astronomy | - |
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