In modulation analysis testing, which of the following does not affect the test frequency applied to the test coil?

In modulation analysis testing, the test frequency applied to the test coil is not influenced by a filter in the test circuit. Filters are used to manage signals within the circuit, such as removing noise or unwanted frequencies, but they do not alter the frequency that is initially applied to the test coil for the test itself.

On the other hand, discontinuities in the test specimen, dimension changes of the specimen, and the chemical composition of the specimen all play significant roles in how eddy currents respond within the material and can impact the effective frequency of the test because they affect the material's properties. For instance, changes in dimensions might alter the skin effect, affecting how eddy currents behave, and variations in chemical composition could lead to differences in conductivity or permeability, further influencing how the test frequency interacts with the material. Thus, only a filter's role is limited to processing the signal rather than affecting the fundamental test frequency applied.