Experiments on Magnetic Tape Readout with an Electron Beam

The electron beam, due to its freedom from inertia' can be made to keep its proper position to recorded information regardless of any deformation experienced by the recording medium in the interval between the recording and the reproduction. In the beam readout system described in this paper, the magnetic tape is bent over a cylinder and the electron beam is made to pass across the recorded track. The electrons close to the tape form a cycloid pattern. This pattern is deflected across the entrance slit of a Faraday collector, thereby producing an output signal corresponding to the recorded information. At present, some practical limitations prevent the full realization of the system's potential. The ultimate limitation is the shot noise of the electrons. Theoretical considerations indicate that a 3-Mc-wide video signal, for example, if suitably recorded, could be reproduced with a signal-to-shot-noise ratio of 30 db and with an area packing density of 0.85 cycle per square mil.