AN ARRANGEMENT IN A TUNABLE MAGNETRON

The invention relates to a tunable magnetron comprising a rotatable tuning element (10) projecting into a ring shaped interaction space between coaxially arranged cathode and anode systems. The tuning element (10) is driven by an electric motor (11) and produces upon rotation a periodic variation of the tuning. The tuning element (10) is situated within the evacuated space of the magnetron and the motor - (11) in situated outside said space. The drive torque of the motor is then transferred to the tuning element via a coupling (12) having two active parts situated one on each side of the evacuated envelope (17) of the magnetron. Such a coupling can only transfer a limited torque. According to the invention the magnetron comprises means for limiting the torque which can be transferred to the coupling (12), both upon starting and stopping, for example a torque limiter (21-26) between the motor (11) and the coupling (12), whereby the start and stop procedures can be performed with optimum torque. Therefore starting and stopping of the tuning element (10), for example when switching between different fixed frequencies, can be made with maximum speed (fig.3).