A Radio-Frequency Device for Detecting the Passage of a Bullet

An unusual application of radio engineering is described in which the reaction of a radio-frequency oscillator to the presence of a metallic projectile in a link-coupled coil is utilized in connection with projectile velocity measurements. In order to obtain the accuracy of signal output required, the circuits are designed for good transient response. In addition, a unique method of differentiating, clipping, and amplifying is utilized in order to obtain a signal with steep wave front when the bullet is at the center of the coil regardless of the weight, shape, or velocity of the bullet. Pictures are included of the equipment and coils used. High-speed pictures of bullets in the tripping position in the coils and oscillograms of circuit voltages verify that circuit operation is as predicted.