Before starting to configure FHEM, one must first configure the machine whoch should wake up. For Ubuntu, there is a great documentation here. No not forget to activate WOL in BIOS; most times, the configuration can be found beyond the menu entries “Wake on LAN” or “Power on PCI/PCIE Devices”.
If everything is set up, copy & paste the IP and MAC adress of the machine to wake up and create a new entry in FHEM:
define MythTV WOL 72:11:AC:4D:37:13 192.168.0.24
Now you have to install etherwake on the FHEM server:
sudo apt-get install etherwake
If WOL works independently from FHEM can be tested using command line:
sudo etherwake 72:11:AC:4D:37:13