Abstract: The invention relates to a resonant cavity device such as a magnetron oscillator which is tunable by means of a tuning plunger associated with sealing bellows. A volume defined at least in part by the bellows and producing a range of spurious responses as the tuning plunger is moved is isolated from the resonant cavity or cavities of the device by an isolating choke. The choke may take the form of an annulus having a major radius of 1/4 .lambda. (where .lambda. is the mid-frequency of the tuning range) attached either to the plunger or to the main body of the device and between the bellows and the resonant cavity or cavities.

Abstract: A method of manufacturing a support framework or truss having at least one suspension element arched in one direction and serving as a roof construction, formed from concrete poured at the site or from prefabricated components, comprising forming a reinforcement construction taking-up the horizontal forces and composed of two horizontal supports arranged in spaced relationship from one another and extending transversely with respect to the arching direction of the suspension element, and which horizontal supports are laterally interconnected by means of reinforcement components, and supporting the thus formed reinforcement construction upon supports. Tension elements for the suspension element are arranged in a spatial curve extending in a catenary configuration between the horizontal supports and are anchored at the region of the supports at the reinforcement construction.