Pulsars are very small objects and to resolve a pulsar magnetosphere you would need an interferometer with a baseline of 14 AU at a frequency 100 MHz. If the angular size of the diffraction pattern at the Earth is less than the angular size of pulsar: θc < θLC then emission regions separated by alight-cylinder radius will produce scintillations that are independent. The interstellar scintillation method presents a unique oppotunity for measuring the angular size of sources with a resolution up to 10−8 arcsec at meter wavelengths.

There were different attempts to resolve pulsar magnetospheres by the scintillation method (Cordes, Weisberg and Boriakoff, 1983, Wolszcan and Cordes, 1987; Smirnova and Shishov, 1989; Smirnova, 1992). Here we present new observations of 4 pulsars: PSR 0834+06, 1133+16, 1237+25 and 1919+21 at a frequency 102 MHz from which we can see evident decorrelation of the pulsar spectrum with increasing space separation between sources in the pulsar magnetosphere.