Patent GB-181514-A (GB)
Title: Improvements relating to high frequency cable telegraphy
IPC: H04L27/10
Filed: 1921-03-24
Abstract: 181,514. Gill, H. A., (Deutsche Telephonwerke Ges.). March 24, 1921. Type-printing telegraphs; wired wireless systems; thermionic amplifiers and modulating systems; heterodyne receiving systems; combined transmitting and receiving arrangements.-The Hughe's type-printing apparatus used in ordinary cable telegraphy is adapted for use in wired wireless systems by mcdifying the electrical connections without substantially altering the apparatus itself. In one form, a valve generator is employed as a transmitter, and the signals are produced by breaking the grid circuit; while at the receiving end a heterodyne generator normally produces beats which cease when the signal is received. In another form, a single valve operates both as transmitter and heterodyne receiver, the signals being sent by slightly varying the frequency of the transmitter so as to make it identical with the frequency of the distant valve, and so causing the beats at the receiving-station to cease. As shown in Fig. 1,. a valve transmitter 1 and a valve receiver 2 are both coupled to the line 3. The transmitter is controlled by raising the switch arm 7 by means of the keyboard and rotary gear of the Hughes' apparatus so as to close the contact 8. The receiving-valve 2 detects the signal from the distant station and, by amplifying-valves 12 and relay 13, closes the circuit of the printing-magnet 15. The outgoing signals may be caused to operate the printing-magnet by providing a mechanical coupling between the switch 7 and the armature of the printing-magnet 15. Alternatively, if the same frequency is used for transmission in both directions, the outgoing signals affect the receiver 2 and so operate the magnet 15. This however may be prevented in order to afford duplex working by employing known balanced or bridge connections between the transmitter and the receiver, or by employing different frequencies. Fig. 2 shows one station of a modified arrangement employing the interference or beat method of reception, the same valve serving for sending and receiving. The valve R' generates high-frequency oscillations in the tuned circuit L' C<1> by virtue of the back coupling between this circuit and the grid circuit. A similar valve at the far station generates oscillations of a slightly different frequency. Both frequencies are normally imposed on the line HL and produce beats at both stations. At the station shown, the beat current appears in the circuit L<2> C<2>, which is coupled by an iron-core transformer to the grid of an amplifier R<2>. the output side of which is coupled to a rectifying-valve R<2> and produces variations of direct current through the receiving- relay ER. When a signal is sent from the far station the two frequencies are brought into agreement, the beats cease, and the relay ER effects the closure of the circuit of the printing-magnet M. In sending from the home station, the switch S of the Hughes' apparatus energizes a relay SR, which cuts in or out a condenser C placed in parallel with the condenser C' of the oscillatory circuit L<1> C<1>, thus either lowering or raising the frequency generated by the valve R'. If the home station is to operate with the higher normal frequency, the switch V<1> is placed in the upper position so that the contact 5 is effective, each signal cutting in the condenser C and lowering the frequency. If the home station operates with the lower frequency, the switch V<1> is lowered on to contacts 10, 12 making the contact 6 effective, so that a signal cuts out the condenser C and raises the frequency. In order to allow signals to be sent by interrupting the generator R<1>, a switch V<2> is depressed so as to break the circuits controlling the condenser C and to place the sending-switch 6 in the grid circuit of the valve R<1>. A tapping-key T' is provided for control purposes, signals being sent by any of the three methods described by depressing this key. The winding of the receiving-relay ER may be shunted by a condenser K and resistance W, and a small condenser C<1> shunted by a resistance S is connected in the grid circuit of the rectifying-valve R<3>. If the Hughes' apparatus S, M, Fig. 2, is to be placed at a distance from the valve apparatus, it is desirable to obviate the use of two double lines F. For this purpose, the modification shown in Fig. 3 is employed. Closure of the sending-switch S completes a circuit for battery B through the single line F, the upper contact 1 of the receiving-relay ER, and sending-relay winding SR. The latter relay closes the contact 3 and so prevents the sending-circuit from being broken at contact 1 by a received signal. Also the relay SR opens the contact 4 and so disconnects the battery HB, which is normally employed for energizing the printing-magnet M over the circuit 4, 2, F, S, when signals are received. The receiving-relay is thus rendered ineffective when the sending-relay is operating. This may also be effected by arranging that the sending-relay SR when energized operates a switch 20 to shortcircuit the receiving-relay winding ER.