CSI Wireless SBX-3, Справочное руководство

Страница: 22 / 110

SBX-3 Reference Manual
4
Various broadcast standards exist for the beacon networks installed
internationally, controlled by their respective operating authority. The
United States Coast Guard maintains a broadcast standard that is
referenced in the Further Reading section of this manual.
1.4 Radiobeacon DGPS Service
The SBX-3 demodulates differential corrections broadcast by DGPS
beacon networks throughout the world. As these stations are installed
and operated with common requirements, when operating the SBX-3, it
will transition between different networks seamlessly.
1.4.1 Radiobeacon Range
The broadcasting range of a 300 kHz beacon is dependent upon a
number of factors including transmission power, free space loss,
ionospheric state, surface conductivity, ambient noise, and
atmospheric losses.
The strength of a signal decreases with distance from the transmitting
station, due in large part to spreading loss. This loss is a result of the
signal’s power being distributed over an increasing surface area as the
signal radiates away from the transmitting antenna. This is analogous
to the walls of a balloon becoming thinner (weaker) as more air is
blown into it.
The expected broadcast range also depends upon the conductivity of
the surface over which the signal travels. A signal will propagate further
over a surface with high conductivity than over a surface with low
conductivity. Lower conductivity surfaces such as dry, infertile soil,
absorb the power of the transmission more than higher conductivity
surfaces, such as seawater or arable land.
A radiobeacon transmission has three components: a direct line of
sight wave, a ground wave, and a sky wave. The line of sight wave is
not significant beyond visual range of the transmitting tower, and does
not have a substantial impact upon signal reception.