Frequency Spectrum Impedance / Interference
(FSI)
Frequency spectrum is the entire range of electromagnetic frequencies used
for communications and other transmissions, which includes communication
channels for radio, cellular phones, and television. In the performance of
typical operations, the military relies on a range of frequencies for
communications and support systems. Similarly, public and private users
rely on a range of frequencies in the use of cellular telephones and other
wireless devices on a daily basis.
Key Terms
Impedance. Impedance is the interruption of electronic signals due to the
existence of a structure or object between the source of the signal and its
destination (receptor). Certain structures have the potential to block, or
impede, the transmission of signals from antennas, satellite dishes, or other
transmission / reception devices affected by line‐of‐sight requirements.
Interference. Interference is the inability to effectively distribute or receive
a particular frequency because of similar frequency competition. As the use
of the frequency spectrum increases (such as the rapid increase in cellular
phone technology over the last decade) and as development expands near
military installations and operational areas, the potential for frequency
spectrum interference increases.
Technical Background
The Department of Defense’s (DoD) use of frequency spectrum allows for
safe operations and the effective delivery of weapons on target without
interference. The need for the DoD’s frequency spectrum testing and
evaluation is constantly increasing, while the spectrum available for DoD use
is decreasing. The National Telecommunications Industry Association (NTIA)
Office of Spectrum Management (OSM) explains that:
Background Report
‘…almost every agency of the Federal Government uses the
spectrum in performing mandated missions. The DoD uses the
spectrum extensively for tactical uses and non‐tactical uses. In the
United States tactical uses are generally limited to a number of
specific testing sites and training facilities, but DoD's non‐tactical
applications are extensive and include aircraft command and
control, mobile communication in and around military bases, and
air fields and long distance communications using satellites.’
Frequency interference is related to other transmission sources and can
result from a number of factors, including:
Using a new transmission frequency that is near an existing frequency;
Reducing the distance between two antennas transmitting on a
similar frequency;
Increasing the power of a similar transmission signal;
Using poorly adjusted transmission devices that transmit outside their
assigned frequency or produce an electromagnetic signal that
interferes with a signal transmission; and
Existing electronic sources and uses created by portable systems
affecting entire communities utilizing Wi‐Fi broadband systems and
industrial sources that produce electronic noise by‐product.
The military relies on a range of frequencies for communications and
support systems. Since 1993, Congress has been selling federal spectrum
bands for reallocation to the private sector, promoting the development of
new telecommunications technologies, products and services. The
expanding public and commercial use of the frequency spectrum from
wireless transmitters to consumer electronics can encroach on the military’s
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