Antenna height and objects in the signal path
Antennas should be installed where they can “see” each other as much as possible. Make sure the antennas are high enough above any obstructions in the radio signal path. You need to check the height of the trees, hills, buildings or other objects on the Radio Path between the antennas with reference to the Radio Path (Fresnel Zone) table below.
Although 2,4 GHz signal pass rather well through walls, they have a difficult time passing through trees. The main difference is the water content in the trees which absorbs 2,4 GHz signal quite well.
|
Object |
Attenuation* of different objects @ 2,4GHz |
| Glass/Window (not tinted) |
10%-15% |
| Interior Drywall |
15%-20% |
| Wood Door |
15%-20% |
| Brick/Concrete wall |
30%-90% |
| Double-pane glass |
60%-70% |
| Steel door |
65%-100% |
*Attenuation = Gradual signal loss
Radio Path
The Radio Path (Fresnel Zone) is the area around the visual line-of-sight that radio waves spread out into after they leave the antenna. You want to keep the Radio Path free of objects to maintain signal strength.
Typically, 20% Radio Path blockage introduces little signal loss to the link. Beyond 40% blockage, signal loss will become significant.
Radio Path (Fresnel Zone) table - Suggested height clear of obstructions:
|
Range |
Optimal height over obstacle (No blockage @ 2,4 GHz) |
Acceptable height without significant performance loss (20% blockage @ 2,4 GHz) |
100m |
1,8m |
1,4m |
250m |
2,8m |
2,2m |
500m |
4,0m |
3,2m |
1000m |
5,6m |
4,5m |
1500m |
6,9m |
5,5m |
Antenna mounting
Make sure your mounting location is as far away as possible from other antennas and upright objects such as flagpoles. Make sure there are no other objects such as a roof gutter or a drainpipe close to the antenna, as they may cause interference and decrease the signal quality.
It is important to mount the antenna vertically; mounting horizontally or at an angle will significantly degrade performance.
Make sure the antennas are aligned to center of the signal path and angle, and on the same level plane.
Correct - Antennas aligned
Wrong - Antennas not vertical/aligned
Suggested mounting
Using L-shaped bracket on a wall
Using L-shaped bracket on an antenna pole
Antenna gain and aiming
7 dBi = 30°
5 dBi = 40°
2 dBi = 360°
Higher gain antennas reach further but require more precise installation/aiming.
Lower gain antennas are more tolerant for installation/aiming mistakes. In some circumstances a lower gain antenna will perform better than a higher gain antenna.
Antenna cable installation
Be careful not to twist or crush the antenna cable or bend it tightly during installation. This can lead to poor performance and signal loss.
Use the minimum cable length required. Do not run more cable than needed.
Do not wrap or coil the cables around anything.