Page 31 - NAVAL FORCES 03/2017

C5I

Features

the earth in a process called ‘refraction’. It is ionosphere on an irregular basis. They can be with little restriction, however bigger files
this process of refraction that allows HF bands caused by a variety of solar activities, such as such as images, which ships in recognition op-
to travel great distances, well over the horizon. solar winds and solar flares, or by ionospheric erations must be able to share with other ships
A number of drawbacks, however, con- events, such as ionospheric storms. These and between navies, do not.
tributed to HF bands losing momentum for a disturbances can cause the refraction of HF
while to the advantage of SATCOM. During radiation to vary significantly, from very high HF reloaded: Europe
nighttime, in the absence of sun radiation, to very low, and therefore can cause HF oper-
free electrons and ions join back together ators to quickly go from a large number of HF Despite these shortcomings, HF radios
into one molecule, thus significantly reduc- frequencies to choose from to a very limited have been making a come back in the industry
ing the number of free electrons present in number. Although they are unpredictable, a over the past few years. This is primarily due
the ionosphere. This reduces the ability of the number of websites now provide information to the fact that, in addition to the long-range
ionosphere to refract HF radiation back toward on the status of the ionosphere at a given time communications they provide, they are also
the earth and therefore limits the number of of the day. interoperable amongst each other. Compared
frequencies available across the HF spectrum. Last but not least, HF is limited in its band- to SATCOM, once the initial investment in HF
The number of frequencies available on the width (19.2 kbit/s) thus restricting the amount equipment has been made there are no addi-
HF wavelength can also be limited by space of data that can be shared between operators. tional call costs or ongoing monthly line or
weather, that is, disturbances that affect the Typically, voice data can travel through HF equipment rental.

NAVAL FORCES III/2017 29