GB340569A - Improvements in or relating to high frequency receiving systems - Google Patents

Abstract

340,569. Wireless signalling. STANDARD TELEPHONES & CABLES, Ltd., Columbia House, Aldwych, London. -(Assignees of Heising, R. A. ; 2, Duncan Street, Millburn, New Jersey, U.S.A.) Oct. 2, 1929, No. 29848. Convention date, Feb. 6. [Class 40 (v).] Relates to shortw a v e heterodyne reception in which an intermediate frequency is derived by combining the incoming signals with a local oscillation of approximately half the s i g n a l frequency, and consists in means for increasing the effective amplitude of the resulting beat frequency. The desired effect is produced by applying to the first rectifier a grid bias of such value that current only flows during the peaks of the local oscillations, and a bigger proportion of the resultant combination wave is suppressed when the signal and local oscillations are 180‹ out of phase than when they are in phase. In this way the resultant intermediate-frequency wave attains a current amplitude comparable with that obtained when the local oscillations are of substantially the same frequency as the incoming waves. In Fig. 2, W and W1 represent two half-cycles of the signal wave superposed upon a local oscillation O of half the signal frequency. When W and O are in phase the resultant is represented by the curve F ; when W1 and O are out of phase the resultant wave is F1. By applying a grid-bias corresponding to P, the portion of the resultant curve below the line 9, 10 is eliminated, with the result that the effective value of the minimum curve F1 is diminished relatively to the value of the maximum curve F, thus increasing the amplitude of the resulting beat frequency. As shown in Fig. 6, the signal frequency f1 is applied in parallel to the grids of the two valves 19, 20, the local frequency 14 being applied to the plate circuits. Here both halfcycles of the local oscillations from 14 are effective, with a corresponding gain in the amplitude of the resulting beat frequency. If the amplitude of the local oscillations is sufficiently large, the directcurrent supply 22 to the plates of the valves 19, 20 can be cut-out by the switch 21.