Radio telescope sensitivity in radiometric observations and the accuracy of signal delay measurements 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 ways to improve their stability are determined. The measured RT-13 radio telescope characteristics 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.