Femtosecond-level synchronization is required for various systems in modern accelerators especially in fourth generation light sources. In those high precision synchronization systems the phase detection accuracy is crucial. However, synchronization to a low noise electrical source is corrupted by a phase detection error originating in the electrical components and connections due to thermal and humidity-related drifts. In future, we plan to implement calibration methods to mitigate these drifts. Those methods require a calibration signal injection, called second tone, into the system. Intrinsically, the injection circuit remains uncalibrated therefore it needs to be drift-free. We performed drift characterization of a set of RF components, which could serve for implementation of a signal injection circuit, namely selected types of couplers and splitters. We describe the measurement setup and discuss the challenges associated with this kind of measurement. Finally, we provide a qualitative and quantitative evaluation of the measurements results
