Mystery component on Yun board?

Official Hardware Classic Yún
10

The reason external antenna is needed is:

  • On board chip antenna has average Gain -0.5 dBi
  • Yun's transmit power is only 17 dBm.
  • Yun is siting at metal case.
  • The distance between Yun and WIFI router is far

Friis Transmission Formula with Propagation Law

  • R = Maximum range for communication link
  • N = Propagation Law (N=2 for line-of-sight, N=4 for urban environments)
  • PT= Transmit power
  • GT= Total antenna gain
  • λ = Wavelength
  • PR= Receiver sensitivity
  • FM= Fading margin

if in urban environments;-

  • Every 12 dBm receiver sensitivity gain will be double the distance.
  • Every 12 dBi antenna gain will be double the distance.
  • Every 12 dBm Transmitter power gain will be double the distance.

in line of sight environments;-

  • Every 6 dBm receiver sensitivity gain will be double the distance.
  • Every 6 dBi antenna gain will be double the distance
  • Every 6 dBm Transmitter power gain will be double the distance.

http://forum.arduino.cc/index.php?topic=175577.msg1304059#msg1304059