A test system for the verification of the quasi-optical converter system is vital in the gyrotron development. For this
reason, an automated measurement setup has been developed and is benchmarked with the TE28,8 mode operating in the cavities of the gyrotrons of W7-X with a high purity of about 95 % and a counter-rotating amount of about 0.3 %. The time duration for the mode generator adjustment has been reduced to two days for this mode. After a successful mode excitation, the quasi-optical mode converter, consisting of a launcher and three mirrors, is measured
having a vectorial Gaussian mode content of 97 %.