I use the HomeMatic system from elv for home automation. A Raspberry Pi 2 with the official transceiver module from HomeMatic as well as the software YAHM ensures trouble-free operation.

The transceiver module is delivered with a small λ/4-wire antenna, which is unfortunately unsuitable to work in my rack.

A SMA socket was built into the case and connected to the module. These SMA pigtails incl. 868 MHz antennas are now available from China for less than 5€.

The result is a significantly improved reception and the possibility to place the antenna outside the rack using an SMA extension cable.