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12
Axis
3™
Chapter 2
Introduction
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 skyward 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. The effect of
fading is that reception may fade in and out. However, this
problem usually occurs in the evening when the ionosphere
becomes more reflective and usually on the edge of coverage
areas. Fading is not usually an issue with overlapping coverage
areas of beacons and their large overall range.
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.
2.4.2
Radiobeacon Messages
Various sources of noise affect beacon reception, and include:
•
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.
Summary of Contents for Axis 3
Page 1: ... Axis 3 TM Operations Manual Part Number 750 1 0060 Rev 2 GPS Receiver System ...
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Page 51: ...43 Axis 3 Appendix C Frequently Asked Questions ...
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