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AIRcable Range Calculation

Wave propagation of AIRcable 2.4GHz products

Path Loss

As waves propagate out from the transmitter, some attenuation of the signal takes place due to properties of the medium (air in this cases). Path loss describes this attenuation as a function of the wavelength of the operating frequency and the distance between the transmitter and receiver. The path loss is derived from the Friis transmission equation and is defined as:

Path Loss = 20 log(4*π*r/λ) dB

where r is the distance between the transmitter and receiver, and at 2.4 GHz, λ=0.125 meters is the wavelength.

Range of AIRcable Products

A link budget analysis can mathematically predict the system range based on the power output, receiver sensitivity, antenna gains, path loss, and fading margin. The path loss equation represents path loss (signal attenuation) as a function of distance between the receiver and transmitter and the wavelength of the operating frequency. This equation is derived from the Friis transmission equation and is given by:

(1) Path Loss = 20* log(4*π*r/λ) dB, where

r = distance between transmitter and receiver λ = wavelength

The Friis transmission equation can be used to represent the path loss as the sum of the other system factors leading to the following equation:

(2) Link Budget = P(t) + G(t) + G(r) - R(s) - F(s) dB,

where P(t) = transmitted power, G(t) = gain of transmit antenna G(r) = gain of receive antenna R(s) = sensitivity of receiver, F(s) = fading margin, (experimentally determined to be 22 dBm)

Now consider the AIRcable SMD module, with an output power of 6dBm, and input sensitivity of -83dBm:

λ = 0.125 meters (for f=2.4 GHz)

(Eq. 1) Path Loss = 105 dB = 20 * log(4*π*r/λ)

(Eq. 2) Link Budget = 6dBm + 3dB + 3dB - (-83dBm) - 22dBm = 73 dB

Setting these equations equal leads to r = 45 meters with the small 4 inch 3 dBi antenna.

Other results with different antennas and the same radio performance.

  • 5.5 dBi = 80m (rubber duck)
  • 8 dBi = 140m (outdoor omni)
  • 15 dBi = 700m (prof omni)
  • 18 dBi = 1.4 km (patch)
  • 24 dBi = 5.6 km (8 degree parabol)
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