[en] Mode purity measurements have been performed at both low and high power (200 kW) on several parts of the ECRH transmission line. This transmission line connects the first 60 GHz gyrotron to the RTP tokamak. Measurements of the mode purity of two gyrotrons showed a high percentage of TE₀₁. This could be reconverted into TE₀₂ by a phase matched TE₀₁-TE₀₂ converter section. The maximum rate-of-rise of the RF-power has been measured. Square wave modulations up to 100 kHz can be made and single pulses of 1 μs have been produced. At this moment ECRH power is routinely applied to the RTP-plasma. (author) 7 refs., 5 figs., 1 tab