Patent GB-392210-A (GB)
Title: Improvements in or relating to short wave radio communication systems
IPC: H01J25/68
Filed: 1931-11-05
Abstract: 392,210. Wireless signalling ; thermionic valves. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, and MATHIEU, G. A., 3, Mayfield Gardens, Shirehall Park, both in London. Nov. 5, 1931, Nos. 30721/31, 32042/31, and 6628/32. [Classes 39 (i) and 40 (v).] An ultra short-wave installation comprises a pair of Barkhausen-Kurz oscillation valves, the grids of which are connected through a tuned Lecher-wire circuit to points on each side of the centre point of a dipole aerial so as to match the surge impedance. The anodes of the valves are inter-connected through a. Lecher-wire circuit, whilst the filaments are similarly interconnected. When used for reception the dipole aerial is connected to the anodes instead of to the grids of the valves. The aerial systems may be of the type described in Specification 389,142. The aerial A, Fig. 1 (30721/31), is provided with end discs b<1>, b<2> which are stated to reduce damping and facilitate external coupling. The aerial doublet is fed from the grids of a push-pull oscillator VI, V2 through Lecher feed-wires f1, /2 which are adjusted to match both the doublet impedance and that of the valves VI, V2. The plates and filaments are connected together either by short leads or by metal plates mounted underneath the valve socket so as to form a condenser indicated at d. A copper tube y supports the transmitting valves and serves also to screen the supply leads. The filament supply from the batteries Ef1, Ef2 is tapped to a voltage node along the Lecher feed wires f3, f4. Modulating potentials are applied to the anodes through a transformer Trl. The aerial is mounted so that it can easily be adjusted into any desired focal position relatively to a parabolic reflector. Alternatively the HT supply may be taken to a point between chokes in the lead connecting the two grids, condensers being inserted in the feed lines to the aerial to allow a thermo-couple or similar radio-frequency meter to be inserted at the electrical centre of the aerial, for regulation and supervision purposes. The aerial, indicator, and part of the feed lines may be housed in a weatherproof glass container, the rest of the installation being enclosed in another weatherproof casing; or the antenna reflector and feeder may have a protecting coating of varnish or enamel. As shown in Fig. 1 (Comp.) the system is tuned in part by the adjustment of the leads f1, /2 and /3, /4 and f5, f6 and f7, /8. The lead 2 connecting the plates is bent back onitself so as not to radiate. Fig. 4 (30721/31) shows certain constructional details and an arrangement of the push-pull valves designed to enable the two sets of connecting leads to be made symmetrical and of equal length. The valves are not symmetrical, i.e. they can not be interchanged. The two grid supports GS and the two plate supports PS are insulated from each other by glass beads, and each end is brought outside the valve independently of the other. Fig. 1 (32042/31) shows a valve construction in which the plate is completely insulated from the socket of the valve, the plate-lead PL being taken out through the sides of the bulb. The sockets of the two pushpull valves may also be arranged so that the plates do not lie parallel to each other. Two push-pull valves may be coupled by a Lecher wire connection between the filaments, as shown in Fig. 5 (30721/31). Or alternatively, they are coupled by prolonging the grid electrodes rearwards from the valve into a Lecher-wire system. One of the push-pull valves may be replaced by an equivalent capacity-network. In reception the plates of' the valves are connected to the aerial and are made slightly positive, relatively to the cathode. By using a local oscillator to impose a plate voltage variation above and below this critical point, a super-regenerative effect is secured. A receiving installation is shown in Fig. 2 (Comp.) the grids being coupled through condensers C4, C5 and a transformer Tr to a low-pass filter LPF and then to a low-frequency amplifier (not shown). Separate readings of the D.C. grid currents are taken on the meters 11, 12. For super-regenerative reception local oscillations are applied from the source AO. Transmitting and receiving aerials may be combined with an aerial doublet which serves as a wave-meter for measuring and adjusting the system to the correct wave-length. A similar wave-meter doublet may be interposed between two transmitting aerials or placed at each end of a series of coupled transmitting aerials. To increase efficiency, two transmitting aerials 2A may overlap three reflectors RFR, as shown in Fig. 4 (Comp,), the aerial1A befng used for reception. For keying, a resistance R, Fig. 1 (6628/32) may be inserted in series with a battery EC to compensate for the rectified A.C, voltage. This is shunted by a valve KV provided with a key in the grid circuit, which varies the effective voltage on the valves VT1, VT2, and so determines whether they oscillate or not. This sytem may be applied to a two-way blocking system for telephony shown in Fig. 2 (6628/32), in which VTl, VT2 are changed from the oscillating condition to a quiescent condition when signals are being received, and vice versa. The keying resistance R is shunted by a tertiary winding W3 on the microphone input. transformer W1 in order to prevent key-clicks when the change-over occurs. Or the same object may be secured by preventing D.C. current from flowing through the winding W1. Specifications 372,660 and 377,535 are also referred to.