Patent GB-190308507-A (GB)
Title: Improvements in Space or Wireless Telegraphy
Inventor: THOMPSON WILLIAM PHILLIPS
Filed: 1903-04-14
Granted: 1903-12-17
Abstract: 8507. Thompson, W. P., [Stone, J. S.]. April 14. Telegraphs.-Relates to systems of wireless telegraphy in which harmonic electromagnetic waves of definite frequency are employed, with receivers which respond only to waves of the frequency to which they are tuned. The invention is directed specially towards the prevention of the tapping of messages not intended for the station, and to protection against attempts to confuse the message. For this purpose, the message is sent by means of separate groups or trains of waves of different frequencies, which produce the signals by their combined effect. Fig. 1 shows two contacts k<1>, k<2> adapted to be closed by the agency of coherers or otherwise on the receipt of waves of frequencies X and Y respectively, which produce disturbances in two vertical conductors. The relays R', R<2> are energized when the respective signals are received, and the receiving-instrument T is only affected when both contacts S<1>, S<2> are closed. Fig. 2 is a diagram showing the signal waves X, Y and the resultant signal S. Fig. 3 shows an arrangement in which the signal does not commence until the contacts k<1>, k<2> have both been closed, but, owing to the shunt circuit 4 and relay R<3>, the relay R<1> remains energized after the circuit 1 has been opened at k<1>, and the signal consequently continues until the train of waves Y, which operates the contact k<2>, ceases. Fig. 4 shows the signal waves and the resultant signal. In the system shown in Fig. 5, the relay R<2> is again placed in the circuit of the receiving-instrument T, so that Y waves are essential to the production of a signal. The relay R', when energized by the closing of the contact k<1>, bricgs its armature on to the contact plate S<24>, but is not powerful enough to close the circuit 5 at S<5>. A powerful battery B", in circuit with a resistance r<14> and a contact S<14> normally closed by a spring, energizes the relay R<1> as soon as the shunting effect of the closed contact k<1> ceases, and the relay is then sufficiently powerful to close the contact S<5> (still maintaining the contact S<24>) and energize the relay R<5>, Thus the arrival and subsequent stoppage of X waves effects the closing of the contact S<1>. If this effect is supplemented by the arrival of Y waves, a signal is recorded, as shown in Fig. 6. Such a signal is, of course, terminated by the cessation of Y waves, but it is also terminated by the re-commencement of X waves, for the consequent closing of the contact k<1> partly de-energizes the relay R', and its armature falls back clear of the contact S<5> though still remaining on the contact plate S<24>. The clearing of the circuits affected by the X waves is performed as follows :-While a current is passing from the battery B<3> through the receiving-instrument T, the armature of the relay R<3> makes contact only with the contact plate S<6>. When, however, the contact at S<2> is broken, the powerful battery B<6> energizes the relay R<3> to a sufficient degree to close the contact S<7>, and thus energize the relay R<7> and open the circuit 14. The armature of the relay R<1> then falls back clear of the contact plate S<24>, and the normal condition of the circuits is resumed. The systems shown in Figs. 3 and 5 may be combined, three trains of waves being employed in the transmission of the signals. Groups of waves of various frequencies, which play no part in the transmission of the message, may be sent out in an irregular fashion to frustate attempts to read the message, or messages may be sent simultaneously in duplicate to independent receiving-instruments, using waves of different frequencies. With regard to the apparatus employed for transmitting and receiving the electromagnetic waves, reference is made to Specifications Nos. 27,253 and 27,272, A.D. 1902.