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"EFFORTS AND FACILITIES AT ELECTRONIC ENVIRONMENTAL TEST FACILITY, FT. HUACHUCA, TO SOLVE RADIO INTERFERENCE PROBLEM OF THE FIELD ARMY."
US Army film MF11-9416
Public domain film from the US National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).
Electromagnetic interference (EMI, also called radio-frequency interference or RFI when in radio frequency) is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit. These effects can range from a simple degradation of data to a total loss of data. The source may be any object, artificial or natural, that carries rapidly changing electrical currents, such as an electrical circuit, the Sun or the Northern Lights.
EMI can be intentionally used for radio jamming, as in some forms of electronic warfare, or can occur unintentionally, as a result of spurious emissions for example through intermodulation products, and the like. It frequently affects the reception of AM radio in urban areas. It can also affect cell phone, FM radio and television reception, although to a lesser extent...
Narrowband EMI or RFI interference typically emanates from intended transmissions, such as radio and TV stations or cell phones.
Broadband EMI or RFI interference is unintentional radiation from sources such as electric power transmission lines.
Conducted electromagnetic interference is caused by the physical contact of the conductors as opposed to radiated EMI, which is caused by induction (without physical contact of the conductors). Electromagnetic disturbances in the EM field of a conductor will no longer be confined to the surface of the conductor and will radiate away from it. This persists in all conductors and mutual inductance between two radiated electromagnetic fields will result in EMI.
Susceptibilities of different radio technologies
Interference tends to be more troublesome with older radio technologies such as analogue amplitude modulation, which have no way of distinguishing unwanted in-band signals from the intended signal, and the omnidirectional antennas used with broadcast systems. Newer radio systems incorporate several improvements that enhance the selectivity. In digital radio systems, such as Wi-Fi, error-correction techniques can be used. Spread-spectrum and frequency-hopping techniques can be used with both analogue and digital signalling to improve resistance to interference. A highly directional receiver, such as a parabolic antenna or a diversity receiver, can be used to select one signal in space to the exclusion of others.
The most extreme example of digital spread-spectrum signalling to date is ultra-wideband (UWB), which proposes the use of large sections of the radio spectrum at low amplitudes to transmit high-bandwidth digital data. UWB, if used exclusively, would enable very efficient use of the spectrum, but users of non-UWB technology are not yet prepared to share the spectrum with the new system because of the interference it would cause to their receivers. The regulatory implications of UWB are discussed in the ultra-wideband article...
Fort Huachuca is a United States Army installation whose garrison is under the command of the United States Army Installation Management Command. It is located in Sierra Vista in Cochise County, in southeast Arizona, about 15 miles (24 km) north of the border with Mexico. Beginning in 1913, for its first 20 years the fort was the base for the "Buffalo Soldiers" of the 10th Cavalry Regiment. During the buildup of World War II, the fort had quarters for more than 25,000 male soldiers and hundreds of WACs. In the 2010 census, Fort Huachuca had a population of about 6,500 active duty soldiers, 7,400 military family members and 5,000 civilian employees. Fort Huachuca has over 18,000 people on post during the peak working hours of 0700 and 1600 on week days, making it one of the busiest Army installations...