The complex demodulation as a spectral technique has been used for the
quasi-continuous determination of the actual frequencies of Schumann
resonances. Applying this method, the first three modes of the vertica
l electric component have been measured regularly in the Nagycenk Obse
rvatory (47.6 degrees N, 16.7 degrees E) since May 1993. (C) 1996 Else
vier Science Ltd