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How to estimate the distance in wireless transmission

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I believe there are many people that would like to know how to estimate the distance in wireless transmission.

Sharing what I got from my FAE to you, but it's based on the transmission theory, so just for reference.

The distance is related to Tx Power, Rx Sensitivity and Operating Frequency

  [Loss](dB)= 32.44 + 20*log D(km)+ 20*log F(MHz)

  Loss = transmission loss (dB)

        D = Distance (Km)

        F = Frequency (MHz)

From the above formula, we could know the loss would increase 6dB when frequency or distance is double.  

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Nice formula!
It seems to be based on the inverse square law (1 / x^2).
http://hyperphysics.phy-astr.gsu.edu/hbase/forces/isq.html

However one thing to note is that it is for free space loss, meaning direct line of sight and in outer-space.
So if you were calculating for a transmission from Earth to Mars, then this formula can work well.

However on Earth ground level, you have things like gases in the atmosphere (air), how much water vapor (humidity) is in the gas can impact signal propagation.
This will change with altitude.

Also for outdoors long distance reflections from the ground, and diffractions from surrounding objects also impact the signal retention.
http://www.wirelesscommunication.nl/reference/chaptr03/pathloss.htm

For indoors, need to consider building materials......
http://ftp1.digi.com/support/images/XST-AN005a-IndoorPathLoss.pdf

There are many things to consider, hence answering "how far can I transmit" is not so easy to answer.


 


 

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1 hour ago, Emplus_Charlie said:

Nice formula!
It seems to be based on the inverse square law (1 / x^2).
http://hyperphysics.phy-astr.gsu.edu/hbase/forces/isq.html

However one thing to note is that it is for free space loss, meaning direct line of sight and in outer-space.
So if you were calculating for a transmission from Earth to Mars, then this formula can work well.

However on Earth ground level, you have things like gases in the atmosphere (air), how much water vapor (humidity) is in the gas can impact signal propagation.
This will change with altitude.

Also for outdoors long distance reflections from the ground, and diffractions from surrounding objects also impact the signal retention.
http://www.wirelesscommunication.nl/reference/chaptr03/pathloss.htm

For indoors, need to consider building materials......
http://ftp1.digi.com/support/images/XST-AN005a-IndoorPathLoss.pdf

There are many things to consider, hence answering "how far can I transmit" is not so easy to answer.

 

I agree with you completely. It's difficult to get a exact number since there are really many things to consider.

 

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I am struggling to get answers on what to expect for range of the engenius radios and they are really no help at all.  Could someone put the above formula to use in an example so I can get some sort of idea of what to expect.  Let's say I have an ENH210EXT as an access point and two ENH202 client bridges.  How does the formula above apply?

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