SmartSight Networks Inc MF24 ユーザーズマニュアル
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Microflex AV/ADV/AVr/ADVr North-American user’s manual / Rev 1.4
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At 2.4 GHz, radio waves are highly attenuated by dense foliage. A link established in the
fall or winter season may be affected adversely in the spring and summertime, if it is
established below tree level.
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At 2.4 GHz, radio waves are highly attenuated by dense foliage. A link established in the
fall or winter season may be affected adversely in the spring and summertime, if it is
established below tree level.
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Once the network RF gain plan has been empirically calculated, the minimum
antenna elevation at each site to minimize path loss should be established. The
Fresnel zone clearance, the earth’s curvature (can be ignored for links shorter
than 12 kilometers) and any physical obstructions along the path have to be
considered.
antenna elevation at each site to minimize path loss should be established. The
Fresnel zone clearance, the earth’s curvature (can be ignored for links shorter
than 12 kilometers) and any physical obstructions along the path have to be
considered.
3.1.3 Verifying Line of Sight and Fresnel Zone Clearance
Unless it is a very short link distance (typically less than 1-2 kilometers) the path
between the two antennas must be free of obstacles that could disturb
propagation. Such path is called a line of sight path. If there are obstacles, radio
waves will be in part absorbed and in part diffracted by the obstacles (multi-path
fading). Even if operating in such circumstances, links could be established.
However, results are highly unpredictable.
between the two antennas must be free of obstacles that could disturb
propagation. Such path is called a line of sight path. If there are obstacles, radio
waves will be in part absorbed and in part diffracted by the obstacles (multi-path
fading). Even if operating in such circumstances, links could be established.
However, results are highly unpredictable.
The first requirement of a successful link is therefore a clear line of sight path.
There is a second requirement related to the beam-width of a radio signal. The
beam-width of a radio signal transmitted between two antennas is an elliptical
area immediately surrounding the visual path (see Figure 9). It varies in
thickness depending on the length of the signal path and the frequency of the
signal. The region outlined by this beam-width is known as the first Fresnel zone.
There is a second requirement related to the beam-width of a radio signal. The
beam-width of a radio signal transmitted between two antennas is an elliptical
area immediately surrounding the visual path (see Figure 9). It varies in
thickness depending on the length of the signal path and the frequency of the
signal. The region outlined by this beam-width is known as the first Fresnel zone.
VISUAL LINE OF SIGHT
FIRST FRESNEL
ZONE (F1)
Figure 9 - Difference Between Fresnel Zone and Visual Line of Sight