In the U.S.,
the Federal Communications Commission (FCC) administers regulations that
divide the RF spectrum into bands and specify uses for each band. The regulations
are in the Code of Federal Regulations, Title 47 (http://wireless.
fcc.gov/rules.html). Part 15 of the regulations covers unlicensed
transmissions.
Many small-scale applications can use bands that allow unlicensed transmissions,
which don??™t require a licensed operator. Transmitters that use these bands
must comply with regulations that apply to the bands, however. The FCC specifies
the allowed radiated power for the fundamental frequency and for radiation
outside the necessary bandwidth. Radiated power is specified as field
strength, which is a measure of the voltage of the radiated signal at a defined
distance from the transmitting antenna. For some bands, the regulations also
specify the allowed type of content and purpose of the transmissions.
Commercial products that intentionally radiate RF energy must obtain certification
by passing FCC compliance tests. The FCC authorizes private test labs
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to perform the tests. On passing compliance tests, the FCC issues an ID number
to the product.
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Designs that don??™t require licensed operators can use any of several RF bands. In
general, to transmit a particular distance, a lower frequency requires less power
but a longer antenna.
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