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The board has a PCB antenna for the 2.5 GHz ISM Band, for stand alone operation on the Camp Area. For other frequencies an external antenna may be needed.
To improve radio reception a little bit you can just press a thumb against the upper right corner and be a human antenna. The most simple real external antenna is a single-wire copper cable (others may also work). This can be pressed against an edge of the little black resistor on the top right corner.
(then the 0 Ohm resistor will be sitting on the R314 pads; R314 and R315 share the upper left pad).
The SMA connector should be an edge-launch SMA connector for a PCB thickness of 1.6mm
Alternative: Add bridge, remove resistor
Using a soldered copper cable as antenna:
Adding an SMA connector so that you can connect an external antenna for your specific needs.
There will be an antenna building workshop at the camp: https://events.ccc.de/camp/2015/wiki/Session:Build_your_own_Antenna_Workshop