Thales MobileMapper Beacon, User Manual

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23
Coast Guard DGPS Service
The MobileMapper Beacon receives differential correction
data transmitted by coast guard stations located in many re-
gions throughout the world.
This chapter aims to provide you with practical knowledge
of this coast guard service, to empower your use of this prod-
uct.
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.
The expected range of a broadcast also depends upon the
conductivity of the surface over which it travels. A signal
will propagate further over a surface with high conductivity
than over a surface with low conductivity. Lower conductiv-
ity surfaces such as dry, infertile soil, absorb the power of the
transmission more than higher conductivity surfaces, such as
sea water 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.
The ground wave portion of the signal propagates along the
surface of the earth, losing strength due to spreading loss, at-
mospheric refraction and diffraction, and attenuation by the
surface over which it travels (dependent upon conductivity).