A technique for designing YIG (yttrium-iron garnet) tuned transistor oscillators, tunable over the range of frequencies from 500 to 950 MHZ, is presented. The approach taken differs appreciably from that used in the design of conventional LC-tuned oscillators. One major difference is that the YIG tuning mechanism is electrically controlled. The YIG tuning element is treated as a single unit and is not resolved into an equivalent LC circuit. Instead, a direct method using reflection coefficients measured at network terminals to characterize various design stages is applied. The transistor is also characterized by reflection and transmission coefficients, i.e., S-parameters. Thus the Smith Chart becomes a useful tool and network calculations are greatly simplified by means of signal flow analysis with application of Mason's rule. Because S-parameters are measured when the device is terminated in the characteristic impedance of the measuring system, they are more accurately determined at high frequencies than other parameters requiring open and short circuit terminations for their measurement. Furthermore, the availability of network analyzers, such as the Hewlett-Packard S-Parameter Test Set, simplifies such measurements. As a result, a concise method using S-parameters is most applicable for the design of transistor YIG-tuned oscillators.