GB368923A - Improvements in or relating to wireless signal receiving apparatus - Google Patents

Abstract

368,923. Wired wireless systems ; valve circuits. HOLMES, H. C., Kiln House Lane, and COMMUNITY RADIO (1928), Ltd., 10, West Crescent, both in St. Anne's-on-Sea. Jan. 26, 1931, No. 2579. [Class 40 (v).] A reception unit adapted to receive one or other of two programmes distributed over the same lines at high and low frequencies respectively comprises a single valve which can be switched to act either as a rectifier or as a low-frequency amplifier. In one embodiment, when the switch J, Fig. 1, is in the position J<2> the valve D is adapted to amplify a low-frequency programme coming from the line through condensers P, P<1>, through the L.F. transformer A, C, the valve being appropriately biased from a tapping F on the grid battery G. When the switch J is in position J<1>, a tuned circuit HK supplies the valve grid with a high-frequency programme, the valve being biased for anode-bend detection from the tapping L. A high resistance E is placed in the lead to the tapping F so that the portion of the grid battery between tappings F and L is not short-circuited when the switch J is in position J<1>. A reaction coil M may be provided, and when a high-frequency programme is being received the connection of coil K across the secondary winding C of the L.F. transformer is said to form a filter to stop low-frequency interference. In a second modification, Fig. 2 (not shown), the grid battery is replaced by a resistance between the valve cathode and H.T. negative. In this case the resistance E may be omitted if the resistance of the portion of the biasing resistance between tappings L and F is smaller than the resistance of transformer secondary C. In another modification, Fig. 3, the inductance K and transformer primary A are connected in series and placed across the line, the tuning condenser H being shunted across the primary A which is made of such an impedance as to affect the tuning only to a small extent. The inductance K functions as a high-frequency choke to prevent leakage of high-frequency currents through the primary A. In a fourth embodiment, Fig. 4, a tuned high-frequency transformer R, Q and the L.F. transformer A, C are shunted across the line and a double-pole switch J selects one or other of the secondaries and during the change-over switches off the filament current. Specification 332,771, [Class 40 (v), Wireless signalling &c.], is referred to.