<p>U radu je predložena modifikovana vatmetarska metoda za merenje snage gubitaka u toroidnim feritnim jezgrima koja je prilagođena osciloskopima male ulazne impedanse. Metoda je verifikovana na komercijalnim uzorcima od Mn-Zn i Ni-Zn feritnih materijala. Metoda je upotrebljena za merenje kompleksne permeabilnosti i gustine snage gubitaka dodatno obrađenih komercijalnih Mn-Zn feritnih prahova. Utvrđeno je da se dodatnim tehnološkim procesima (mlevenjem i prosejavanjem) početnog komercijanog praha mogu napraviti feritna jezgra manje gustine snage gubitaka i veće permeabilnosti.</p> / <p>The thesis proposes a modified Watt-meter method for measuring core loss of ferrite cores, which is adjusted to oscilloscopes with the small input impedance. The method is verified on comercial Mn-Zn and Ni-Zn ring cores. The method is used to measure the influence of starting powder sieving and milling on the core loss density and permeability of Mn-Zn ferrite. The experimental results and calculations show the significance of the additional milling and sieving process on magnetic properties of Mn-Zn ferrite in the frequency range from 0.1MHz to 10MHz. These processes increase the relative permeability about 3 times and decrease the core loss 4 times by milling of the starting powder.</p>