  Tunka-Rex, the Tunka Radio extension at the TAIGA facility (Tunka Advanced
Instrument for cosmic ray physics and Gamma Astronomy) in Siberia, has recently
been expanded to a total number 63 SALLA antennas, most of them distributed on
an area of one square kilometer. In the first years of operation, Tunka-Rex was
solely triggered by the co-located air-Cherenkov array Tunka-133. The
correlation of the measurements by both detectors has provided direct
experimental proof that radio arrays can measure the position of the shower
maximum. The precision achieved so far is 40 g/cm^2, and several methodical
improvements are under study. Moreover, the cross-comparison of Tunka-Rex and
Tunka-133 shows that the energy reconstruction of Tunka-Rex is precise to 15 %,
with a total accuracy of 20 % including the absolute energy scale. By using
exactly the same calibration source for Tunka-Rex and LOPES, the energy scale
of their host experiments, Tunka-133 and KASCADE-Grande, respectively, can be
compared even more accurately with a remaining uncertainty of about 10 %. The
main goal of Tunka-Rex for the next years is a study of the cosmic-ray mass
composition in the energy range above 100 PeV: For this purpose, Tunka-Rex now
is triggered also during daytime by the particle detector array Tunka-Grande
featuring surface and underground scintillators for electron and muon
detection.
