Patent GB-190227272-A (GB)
Title: Improvements in the Method of Selective Electric Signalling
Inventor: STONE JOHN STONE
Filed: 1902-12-10
Granted: 1903-11-12
Abstract: 27,272. Lake, H. H., [Stone, J. S.]. Dec. 10. Telegraphs.-Telegraphy is effected by passage of simple harmonic electromagnetic waves of high frequency through space between two vertical or inclined conductors, which are preferably as far as possible aperiodic, but are connected through induction coils with tuned circuits so that only waves of definite frequency can be received or sent. The elevated conductor may, however, also be tuned to the definite frequency. Each elevated conductor V is connected through one winding of an induction coil M to earth. The other winding of the coil M forms part of a circuit containing in series one or more condensers C and adjustable inductances L, so as to have a definite natural oscillation rate, which is the same for each transmitter and the corresponding receiver. In one arrangement of transmitting- system, shown in Fig. 7, the circuit C, L is an intermediate circuit, and includes one winding of an induction coil M' ; the other winding of this coil is in an oscillator circuit, which contains a spark-gap S, a condenser C<1>, and an inductance L', and has the same natural oscillation rate as the intermediate circuit C, L. Electric oscillations are set up in the oscillator cirsuit C', L' by an ordinary induction coil M", a battery B, a contact-breaker p, and a primary condenser C", when a key k is closed. An alternator may be used in place of the battery &c. The condensers C, C' and coils L, L', M, M' are made to have as little dielectric or magnetic hysteresis as possible, and the coils with little dielectric capacity. Under these conditions simple harmonic oscillations of one frequency are set up in the circuits C', L' and C, L, and the vertical conductor. The inductances L, L' are made large relatively to the mutual inductance in the coil M, in order to stop any oscillations of different frequency received from the vertical conductor. The receiving- circuits are similar, but the spark-gap S is replaced by a condenser of large capacity, and the coil M" is omitted, the terminals of the condenser C<1> (or of the condenser C' and inductance L' together) being connected to a coherer and to a local relay circuit ; or the coherer may be inserted in place of the spark-gap S. The coherer &c. may be replaced by a telephone or other receiver. The intermediate circuit C, L at both the sending and receiving ends is employed to reduce oscillations not of the particular frequency desired, and may be omitted, or more than one such intermediate circuit may be used, in series. Each vertical conductor may be connected to earth through windings of two or more separate induction coils, such windings being connected either in series or parallel ; the other windings of the coils are in separate transmitting or receiving circuits, arranged for different frequencies. Or the vertical conductor may contain only one winding, this being in inductive relation to two or more windings in different transmitting or receiving circuits. Messages may thus be sent from one vertical conductor to any desired receiving-stations. The condensers used have air insulation. The coils are made with small distributed capacities, in order that they may not in themselves be appreciably resonant to any frequency. They may be flat spirals or other coils supported on open frames, the turns being openly wound to reduce the displacement currents between them at high electric pressure and frequency. The Specification indicates a method of calculating whether any particular coil is suitable, from its dimensions and measured self-inductance, and the frequency to be employed.