Patent GB-190619881-A (GB)
Title: Improvements in and relating to Wireless Telegraph Systems.
Filed: 1906-09-06
Granted: 1907-06-20
Abstract: 19,881. De Forest Wireless Telegraph Syndicate, [Forest, L. de]. Sept. 6. Telegraphs.-Relates to wireless telegraph systems, in which the receiving operator can cut in upon and interrupt the operator at the transmitting-station. As shown in Fig. 1, separate antennee are provided for transmitting and receiving. The transmitting-antenna A is insulated at its upper end, and the conductors are separated by a spreader K guyed by ropes V. The receiving- antenna A<1> is conductively connected to the rod J<1> and may be fixed at the required height by a cable. On closing the circuit of the generator G by a key k, a condenser C discharges across the gap S, setting up high-frequency oscillations which are conveyed to the antenna A by an auto-transformer L. The periods of the oscillation circuit and antenna are preferably made equal by adjusting the contacts c, c<1>. By adjusting contacts d, d', the period of the antenna A' is made equal to that of the receiving-circuit, which includes the responder R, variable condenser C", and inductance L". The local circuit shunting receiver R includes a telephone T and potentiometer. A switch 0 connects the two sides of the antenna 1, 1 and 2, 2 to the receiving-apparatus during the receipt of messages and disconnects them during transmission. As separate antennae are employed, only a small lowpotential switch is required. In a modification, the antenna wires are connected to two terminals of an anchor spark-gap, the third terminal of which is earthed, and another anchor spark-gap shunts a portion of the inductance L", so that oscillations created in the receiving-antenna by the transmitting-antenna A pass to earth without affecting the receiver R. As a further protection, the receiver R may be shunted automatically when the key k closes the generator circuit. The anchor spark-gaps do not interfere with the reception of signals, as the potentials developed are too feeble to bridge the gaps, and the circuit of the battery is opened when the receiver is short-circuited, in order to prevent the battery from running down. In a further modification, one terminal of the receiver R is normally immersed in the electrolyte, but is removed therefrom when the key is depressed. The transmitting and receiving antennµ may be supported by separate masts, such masts being sufficiently far apart to permit of duplex working, and the stations may be connected by a ' pony' telegraph line. Fig. 5 shows another system, in which a receiving-operator can interrupt a transmitting - operator ; only one antenna is required, the wires of which form a loop. The ground-lead is connected to the antenna directly below the anchor spark-gap s, s<1> and above the transmitting-helix L, thus obviating the necessity for large switches to protect the responder. The receiving-circuit d', C', R, d, L<1> is tuned to the frequency of the antenna, and the responder R comprises a vessel containing an electrolyte and a glass-enclosed anode U carried by an iron plunger V surrounded by the solenoid W. When the key k is depressed, and before it closes the circuit of the generator G, the spring, carried by and insulated from the key K, closes the circuit of the solenoid Wand battery B<1> at the point h, causing the plunger to lift the anode U out of the electrolyte ; when the key closes the circuit of the generator G, oscillations are set up and translated to the antenna by the auto-transformer L. The dielectric strength of the anchor spark-gap s, s', which comprises two plates m, m<1> having a large number of fine teeth, abutting upon an adjustable centre plate n, is large enough to maintain the antenna as a loop while receiving, but the oscillations employed in transmission readily bridge this gap. The condenser shown at C in Figs. 1 and 5, and in Fig. 8, comprises a vessel of earthenware or insulating-material filled with oil, which may be under pressure, in which are disposed plates of brass 6 alternately insulated from each otber, and the vessel may be closed by an insulating-plate 2. Several modes of arranging the antennae are described. The cable H, Fig. 10, carries members K having insulators J to which the wires of the transmitting-antenna are attached, each wire forming a loop and being held in position by guys B, B having strain insulators C. The receiving-antenna is a loop, the two sides of which extend approximately in the plane of the masts and are held in position by guys B<1> having strain insulators C<1>. It is supported by insulators J<1> and an approximately horizontal portion extends between the masts. In modifications, a number of wires form the receiving-antenna, which are not necessarily horizontal, and the masts and antennm are approximately separated by a quarter-wave length to obtain a cumulative effect. Or each mast may be provided with a separate receiving-antenna having separate receiving-instruments so related to a signal-indicating instrument that the latter is operated by the cumulative effect of the receiving-instruments.