GB399549A - Improvements in or relating to radio receivers suitable for use adjacent internal combustion engines - Google Patents

Abstract

399,549. Wireless receiving systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, and LINSELL, A. A., 43, West Hill, Sydenham, both in London. April 7, 1932, No. 10028. [Class 40 (v).] Relates to means for minimizing interference with wireless reception, on an aeroplane or motor-car, due to shockexcitation from the magnet of the internal-combustion engine. According to the invention the receiver is rendered inoperative during the actual " firing " periods by heavily damping the tuned circuits. Since firing only occupies a small fraction of the total time, the reception of signals is substantially unaffected. Alternatively a variablemu valve is used to reduce amplification during the firing periods. In Fig. 1 the neon tube NT, shunted across the input circuit LC of the receiver, is " flashed " each time the sparking-plug SP fires. In Fig. 3, the flashing of the neon tube NT imposes a positive gridbias which renders the valve V conductive, and so damps the HF circuit. The periodicity of the damping may be arranged to coincide with the " quenching " periods of a receiver of the super-regenerative type. In Fig. 4 an iron segment IS on a rotating disc D mounted on the magneto shaft induces a periodic voltage which is applied, either directly or after rectification and amplification, to render a neon tube conductive, or to operate a short-circuiting relay across one of the tuned circuits. Alternatively the induced voltage from the ignition system may be rectified at CD, Fig. 5, and applied to the grid of a variable-mu valve MV to reduce its amplification factor. Energy may be transferred from the magneto to the damping- device through an hydraulic power line, which may be earthed, instead of through electric coupling-lines. According to the Provisional Specification, an auxiliary " damping " valve is shunted across the tuned HF circuit, and comprises a " timing " circuit to limit the duration of the inoperative periods.