Abstract: For the electrical testing of base material for manufacturing printed circuit boards, firstly smooth edges to the copper layers of the base material, free of deformation, are produced, preferably in a milling process, which base material is subsequently subjected to testing for a sufficiently high level of electrical resistance between the two copper layers. Successful resistance testing is followed by testing for the dielectric strength of the insulating layer of the base material by measuring the current conduction produced as a result of a disruptive breakdown. This process serves to reduce the amount of processed base material which is rejected, on which, at the present state of the art, there is no electrical testing prior to processing.

Abstract: The invention involves a method for digital transmission of messages in a digital radio relay system which utilizes a superframe so additional information can be transmitted with a digital signal. This method eliminates the simulation of a frame alignment signal by service bits. In this invention m superframes each consisting of two half-frames containing a byte for additional bits and in which a scrambling of the digital signals takes place by adding a periodic bit pattern to the digital signal, are combined to form a multiple frame. The pattern used for scrambling has a period equal to the length of the multiple frame.

Abstract: An annular reinforcement for piston ring grooves, the reinforcement being provided with inclined bores so that when the reinforcement is built into the piston and the bores are filled with material integral with the piston, movement of the reinforcement both in the axial and radial directions is resisted.