1-11
1-1 shows the radio-frequency spectrum broken down into nine bands used by the military. Propagation
of radio waves varies widely at different frequencies. Frequencies and equipment are chosen to meet the
communications application desired. We will discuss the radio-frequency spectrum in the following
paragraphs.
Table 1-1.—Radio-Frequency Spectrum
FREQUENCY
DESCRIPTION
30 GHZ - 300 GHZ
extremely high frequency
3 GHZ - 30 GHZ
superhigh frequency
300 MHZ - 3 GHZ
ultrahigh frequency
30 MHZ - 300 MHZ
very high frequency
3 MHZ - 30 MHZ
high frequency
300 KHZ - 3 MHZ
medium frequency
30 KHZ - 300 KHZ
low frequency
3 KHZ - 30 KHZ
very low frequency
300 HZ - 3 KHZ
voice frequency
Up to 300 HZ
extremely low frequency
Extremely Low-Frequency Communications
The purpose of the EXTREMELY LOW-FREQUENCY (elf) communications system is to send
short "phonetic letter spelled out" (PLSO) messages from operating authorities in the continental United
States (CONUS) to submarines operating at normal mission speeds and depths. Elf has the ability to
penetrate ocean depths to several hundred feet with little signal loss. This ability allows submarines to be
operated well below the immediate surface and enhances submarine survivability by making detection
more difficult.
This is a one-way communications system from the operating authority to submarines at sea. The
large size of elf transmitters and antennas makes elf transmission from submarines impractical.
Very-Low-Frequency Communications
The communications commitments of the Navy now cover the face of the earth. New sea frontiers to
the north have opened a four-million-square-mile, ice-covered ocean of strategic importance. Our Navy
must maintain control of the operating forces in an ever expanding coverage area. This additional area
requires changes in communications capacity, range, and reliability. Additional needs have been
particularly great in the North Atlantic and the newly opened Arctic Ocean. High-frequency circuits are
too unreliable in these areas because of local atmospheric disturbances.
