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 2nd and 4th 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.