We present a method newly developed at the Astrophysikalisches Institut Potsdam (AIP) for determining the structure and the strength of coronal magnetic fields during the late phase of solar flares. Fiber bursts Fiber bursts are a spectral fine structure occuring in some type IV radio burst continua. Here we assume that the fiber bursts are excited by whistler waves and their interaction with nonthermal electrons trapped in a magnetic loop. […]