A large sample of pulsars has been observed to study their subpulse modulation at an observing wavelength (when achievable) of both 21 and 92 cm using the Westerbork Synthesis Radio Telescope. In this paper we present the 92-cm data and a comparison is made with the already published 21-cm results. The main goals are to determine what fraction of the pulsars have drifting subpulses, whether those pulsars share some physical properties and to find out if subpulse modulation properties are frequency dependent. We analysed 191 pulsars at 92-cm searching for subpulse modulation using fluctuation spectra. The sample of pulsars is as unbiased as possible towards any particular pulsar characteristics.