GB605878A - Angle modulated carrier wave detector - Google Patents

Abstract

605,878. Frequency modulation; circuits for cathode-ray tubes. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. July 13, 1945, No. 17986. Convention date, July 14, 1944. Addition to 605,715. [Classes 40 (v) and 40 (vi)] [Also in Group XL (a)] A detector for angle-modulated carrier waves comprises a discriminator for deriving a pair of high-frequency voltages whose relative magnitudes vary in accordance with the frequency of the applied wave, a cathode-ray tube having an output electrode with at least two areas of different secondary electron. emissivity, and deflector elements to sweep the primary electron beam over the-two areas in response to the high-frequency voltages to vary the output electrode current. The discriminator of a frequency-modulated superheterodyne receiver, Fig. 1, consists of a primary tuned circuit 13 coupled to two off-tune circuits 15, 16 which are connected to the deflection plates 5, 6 of a cathode-ray tube 1. The cathode-ray tube has a focussing electrode 4 and two pairs of deflection plates 5, 5<1>, 6, 6<1>, one of each pair being earthed. The primary electron beam 3 is swept in an elliptical path over the circular target T in response to the relative amplitude variations in the H.F. voltages appearing at the deflection plates. The target T has four equal sectors of different secondary electron emissivity, the diametrically -opposed sectors is maintained at a lower positive potential than the collector 'electrode E, which is constructed so as to permit the passage of the primary beam 3 in which it is placed. As the frequency of the received wave varies, the pattern traced on the target T by the primary electron beam 3 changes, thus varying the width and recurrence frequency of the output pulses which appear across resistance R. Since the shape of the pattern traced on target T by beam 3 is independent of the amplitude of the received wave, and the output voltage of target T does not depend on the size of the trace, the signal appearing across integrating condenser 11 is independent of amplitude variations in the received wave. In a modification, Fig. 5, the target T has a central hole 30 slightly larger in diameter than the electron beam, so that no output appears across resistance R when no signal is present, thus reducing noise effects. U.S.A. Specification 2,344,679 is referred to.