  Using a recently developed two-scale formalism to determine the magnetic
helicity spectrum (Brandenburg et al. 2017), we analyze synoptic vector
magnetograms built with data from the Vector Spectromagnetograph (VSM)
instrument on the \emph{Synoptic Optical Long-term Investigations of the Sun}
(SOLIS) telescope during January 2010-July 2016. In contrast to an earlier
study using only three Carrington rotations, our analysis includes 74 synoptic
Carrington rotation maps. We recover here bihelical spectra at different phases
of solar cycle~24, where the net magnetic helicity in the majority of the data
is consistent with a large-scale dynamo with helical turbulence operating in
the Sun. More than $20\%$ of the analyzed maps, however, show violations of the
expected sign rule.
