35-year cycle in solar activity in 1000−1900

We performed a Fourier and wavelet analysis of solar activity in the range between the period of the Hoyle magnetic cycle (~22 years) and the Gleisberg cycle (50-120 years) in 1000-1900. Two reconstructions of the number of sunspots from indirect data were used based on: a) the number of low-latitude auroras and b) the concentration of 14C in tree rings. Our analysis showed that in the spectra of both reconstructions, there is a pronounced stable variation with a period of ~30-40 years, which is present even during grand minimums/maxima. The source of this variation is the frequency modulation by the Suess cycle with a period of ~200 years, resulting in a three-frequency structure with carrier oscillation with a period of ~35 years and sideband periods of ~30 and ~40 years. Some difference in the obtained spectra of the two reconstructions may be due to the different contribution of closed and open magnetic fields in the restoration of solar activity from different indirect data.