Signal Loss by Diffraction Calculator

Signal Loss By Diffraction: It is common for radio and Wifi signals to be diffracted by objects in their path. This happens to all EM radiation like visible light for example. The effect is to bend some of the signal round an obstacle and pass some signal energy in other directions.

Sky is blue by Diffraction

Signal Loss By Diffraction – The effect of wave length

The effect is accentuated by the shorter the wavelength of the radiation, the more bending effect takes place the shorter the wavelength. This corresponds to higher frequencies. So for high frequency links the effect is more pronounced and there is more signal loss by diffraction.

Diffraction – Why the Sky is Blue

As a interesting observation the diffraction of light has an every day effect on all of us. Sun light passing through our atmosphere is diffracted by the moisture and the air it passes through. Light is composed of all the visible wave lengths from deep red to the blues and indigos of the rainbow. The blue light has a shorter wave length than than the red wave length so is diffracted more than the red. So in effect we see a blue sky. The sky has acted like a blue filter during the day.

Diffraction – Why We Get Red Sunsets

As the sun passes to the horizon at the end of the day. The blue light in it has been almost filtered away due to the length of the path through the atmosphere the light has taken to reach you. The red light has a much longer wave length and consequently is not diffracted as much. In this case we get red sun sets and the sky is acting like a red filter.

Signal Loss By Diffraction Calculator

We want to take account of the obstacles in planning point to point link budgets so here is a handy calculator to account for signal loss by diffraction. Use the image diagram and enter the corresponding values for D1, D2 and h.

Wifi Diffraction Calculator

Frequency Band:
Height “h” between antenna top and obstacle top [meters]
Distance “D1” between transmitter and obstacle [meters]
Distance “D2” between receiver and obstacle [meters]

Useful Tools for Signal Link Budget Calculation

There are many other factors affecting our plans to create wifi links and some of these are covered in other tools on this blog.Here is a page covering Link Budget Calculation