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.


Example at 500-meter range


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


Acceptable – but exact alignment of antennas necessary


Wrong - Antennas not 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

9 dBi = 25°
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.