563489578934

Sec. 1–7 Frequency Allocations 11
The Telecommunications Standardization Section (ITU-T) examines technical, operating, and
tariff questions. It recommends worldwide standards for the public telecommunications
network (PTN) and related radio systems. The Telecommunication Development Sector
(ITU-D) provides technical assistance, especially for developing countries. This assistance
encourages a full array of telecommunication services to be economically provided and
integrated into the worldwide telecommunication system. Before 1992, the ITU was organized
into two main sectors: the International Telegraph and Telephone Consultative Committee
(CCITT) and the International Radio Consultative Committee (CCIR).
Each member nation of the ITU retains sovereignty over the spectral usage and standards
adopted in its territory. However, each nation is expected to abide by the overall frequency plan
and standards that are adopted by the ITU. Usually, each nation establishes an agency that is
responsible for the administration of the radio frequency assignments within its borders. In the
United States, the Federal Communications Commission (FCC) regulates and licenses radio
systems for the general public and state and local government (see http://www.fcc.gov). In addition,
the National Telecommunication and Information Administration (NTIA) is responsible
for U.S. government and U.S. military frequency assignments. The international frequency
assignments are divided into subbands by the FCC to accommodate 70 categories of services
and 9 million transmitters. Table 1–2 gives a general listing of frequency bands, their common
designations, typical propagation conditions, and typical services assigned to these bands.
TABLE 1–2
FREQUENCY BANDS
Frequency
Band a
Designation
Propagation
Characteristics
Typical Uses
3–30 kHz Very low
frequency (VLF)
30–300 kHz Low frequency
(LF)
300–3000 kHz Medium frequency
(MF)
3–30 MHz High frequency
(HF)
30–300 MHz Very high
frequency (VHF)
Ground wave; low
attenuation day and
night; high atmospheric
noise level
Similar to VLF, slightly
less reliable; absorption
in daytime
Ground wave and night
sky wave; attenuation
low at night and high in
day; atmospheric noise
Ionospheric reflection
varies with time of day,
season, and frequency;
low atmospheric noise
at 30 MHz
Nearly line-of-sight (LOS)
propagation, with
scattering because of
temperature inversions,
cosmic noise
Long-range navigation;
submarine
communication
Long-range navigation and
marine communication
radio beacons
Maritime radio, direction
finding, and AM
broadcasting
Amateur radio; international
broadcasting, military
communication, longdistance
aircraft and ship
communication, telephone,
telegraph, facsimile
VHF television, FM
two-way radio, AM
aircraft communication,
aircraft navigational aids
a kHz = 10 3 Hz; MHz = 10 6 Hz; GHz = 10 9 Hz.