Calibration of the absolute amplitude scale of the Tunka Radio Extension (ICRC 2015)

The Tunka Radio Extension (Tunka-Rex) is an array of 44 radio antenna stations, distributed over 3 km$^{2}$, constituting a radio detector for air showers with an energy threshold around 10$^{17}$ eV. It is an extension to Tunka-133, an air-Cherenkov detector in Siberia, which is used as an external trigger for Tunka-Rex and provides a reliable reconstruction of energy and shower maximum. Each antenna station consists of two perpendicularly aligned active antennas, called SALLAs. An antenna calibration of the SALLA with a commercial reference source enables us to reconstruct the detected radio signal on an absolute scale. Since the same reference source was used for the calibration of LOPES and, in a calibration campaign in 2014, also for LOFAR, these three experiments now have a consistent calibration and, therefore, absolute scale. This was a key ingredient to resolve a longer standing contradiction between measurements of two calibrated experiments. We will present how the calibration was performed and compare radio measurements of air showers from Tunka-Rex to model calculations with the radio simulation code CoREAS, confirming it within the scale uncertainty of the calibration of 18%.