CSI Wireless SBX-3, Справочное руководство

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SBX-3 Reference Manual
5
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
to fade. Fading occurs when the ground and sky waves interfere with
each other constructively and destructively, potentially causing
reception to come and go. This problem usually occurs in the evening
when the ionosphere becomes more reflective and typically is only
significant on the edge of coverage areas. Fading is not usually an
issue in regions with overlapping coverage from multiple beacons and
is considered during the design phase of the beacon network.
Atmospheric attenuation plays a minor part in signal transmission
range, as it absorbs and scatters the signal. This type of loss is the
least significant of those described.
1.4.2 Radiobeacon Reception
Various sources of noise affect beacon reception, including:
•
Engine noise
•
Alternator noise
•
Noise from Power lines
•
DC to AC inverting equipment
•
Electric devices such as CRT’s, electric motors, and solenoids
Noise generated by this type of equipment can mask the beacon signal,
reducing or impairing reception. Section 4.1 presents an effective
antenna installation procedure to minimize the impact of local noise on
beacon reception.