A key design process in the construction of a waveguide cavity or component is the so-called cold test stage. This involves measuring the response of the component to radiation, propagating with a specific electromagnetic mode and a certain frequency, or range of frequencies. However, for components that require testing with high order modes, such as resonant cavities used in high-power, or high-harmonic gyrotrons, it can be challenging to generate the necessary mode. A scheme for co-harmonic generation of radiation through the cyclotron resonance maser (CRM) instability has previously been proposed. Such a scheme involves the generation of two separate harmonics of the electron cyclotron frequency, specifically the 2 nd and 4 th harmonics, within the same geometry. The two electromagnetic modes stimulated are the TE 2.2 and TE 4.3. Unfortunately, the generation of these two modes for cold testing purposes is not a trivial matter.