The measurement accuracy of Ql depends on the quality of RF components in the RF drive line. The components that could significantly affect Ql measurement are the circulator and the directional coupler. When the forward power is shut off and the decay seen on the cavity probe is being measured, power is also going out of the cavity into the RF drive line. The output return loss of the RF components in the RF drive line (circulator, cables, and coupler) will reflect power coming out of the cavity and inject power back into the cavity, which will change the decay seen on the cavity probe. We will assume, for these simulations that the cables do not significantly contribute to the reflections. The purpose of this note is determine that relationship of Ql measurement errors and RF component specification. Most specifically, the output return loss of the above components.