Radio telescope sensitivity in radiometric observations and the accuracy of signal delay measure-
ments in radio interferometric observations are largely determined by the amplitude and phase
instability of the receiving equipment. To identify the sources of this instability, an urgent task is
to create methods and equipment to measure the instability of the receiving system as a whole and
its individual stages in particular. The paper presents a developed hardware-software complex,
methods, and investigation of the amplitude and phase stability of the "Quasar" VLBI Network
radio telescope receiving systems. The main sources of instability of the receiving systems and
waystoimprovetheirstabilityaredetermined. ThemeasuredRT-13radiotelescopecharacteristics
obtained by the created hardware-software complex are presented. A method to determine the
optimal signal averaging time of a radio interferometer has been developed, which reduces the
error in determining the UT1−UTC corrections.