CSI Wireless ABX-3, Reference Manual

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ABX-3 / MBX-3 Reference Manual 4
1.4 Radiobeacon DGPS Service
The ABX-3 and MBX-3 receivers are able to use differential corrections
received through the internal beacon receiver, operating seamlessly
with DGPS beacon networks throughout the world.
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.
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 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.
The ground wave portion of the signal propagates along the surface of
the earth, losing strength due to spreading loss, atmospheric refraction
and diffraction, and attenuation by the surface over which it travels
(dependent upon conductivity).
The portion of the beacon signal broadcast skywards is known as the
sky wave. Depending on its reflectance, the sky wave may bounce off
the ionosphere and back to Earth causing reception of the ground wave