Arduino Yun external antenna
There's a discussion on the Arduino Forum about this:

Mystery component on Yun board?

From what I read it's only for testing purposes.


  the connector is a MM8430-2610 (see this). You can plug in a
  MXGS83RK3000/MM126036: once plugged in, the switch connector will turn
  the internal antenna off and use the probe as an external antenna