Dependence of the power spectrum of Pc 3-4 magnetic pulsations observed at the ATS 6 geosynchronous satellite on the interplanetary magnetic field (MF) has been studied. Pulsation events that were observed near noon and exhibited harmonic structure are chosen for analysis. We further select pulsation events with identical fundamental frequency to study dependence of the power of pulsations at different harmonic bands on the IMF. A weak negative correlation is observed between the IMF cone angle &THgr;XB and the power of pulsations in the frequency range 20--70 mHz. Also, a positive correlation between the intensity of the IMF (BIMF) and the power of pulsations at 50--79 mHz is found. This BIMF control is present at all ranges of the cone angle. We compare this observation with the frequency of bow shock associated upstream waves predicted from a model of wave generation by a cyclotron resonance of ions reflected at the bow shock. The predicted frequency depends on the IMF cos2 &thgr;XB. Although this relation gives a proportionality between the frequency and BIMF qualitatively consistent with the observation, it does not explain the most obvious IMF control of the spectrum of the pulsations.