Calculate the Clearance of an Obstruction

VSAT LoS Issue

If you think you may have a line of sight blockage to the satellite and want to check the distance away from the obstruction (trees, buildings, mast, etc.) you need to be then some simple maths should see you out of a pickle.
We can use some simple trigonometry mathematics to calculate the distance we need to be away from the obstruction to get a clear line of sight to the satellite. We can use Tangent for this.

Calculating the Clearance Needed

 

  • Firstly, measure the distance from the VSAT antenna to the base of the obstruction (Distance)
  • Measure (estimate if you cannot measure) the height of the obstruction (Height). If you have an inclometer with a % scale then walk away until you measure 45% elevation to the obstruction. This will mean that the height of the obstruction is equal to the distance you are away from it. Confused yet?
  • Calculate the elevation to the satellite (Elevation).

 

Calculating Clearance Distance for VSAT

The Formulas

Tangent  = Opposite / Adjacent

 

Tan Elevation° = Height / Distance

∴ Distance = Height / (Tan Elevation°)

 


Example

You’ve been sent to a remote site to install a 1.8m antenna. Unfortunately, no one asked about the location of the antenna and if any buildings might be in the line of sight to the satellite. After not being able to find the sat for a few hours you measure the distance to the building roof as 15m and estimate it’s 6m tall and your elevation is 32°.

Distance = 6m / (Tan 32° ) = 9.6m

As you can see you must be at least 9.6m away from the building to get a clear line of sight to the satellite, but you would want to be further away as this to allow for any errors and to clear the building roof with a buffer zone.
So being 15m away you will clear the building roof so I’d go back to basics if you still cannot find the satellite.

satoms Author

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