Patent GB-357631-A (GB)
Title: Improvements in or relating to radio signalling systems
IPC: H04B3/20
Filed: 1930-06-26
Abstract: 357,631. Two-way terminal equipment. STANDARD TELEPHONES & CABLES, Ltd., Columbia House, Aldwych, London.-( Western Electric Co., Inc. ; 195, Broadway, New York, U.S.A.) June 26, 1930, No. 19470. [Class 40 (iv).] In a radio system comprising a transmitting station and a receiving station located in the same neighbourhood and connected to a terminal station, a switching device is provided at the transmitting station responsive to voice currents in the line between the transmitting and terminal stations for disabling the line between the receiving and terminal stations. In addition, auxiliary voice-operated equipment responsive to signals from the local transmitting aerial but non-responsive to signals from the distant aerial, may be provided at the receiving station for disabling the receiver. The invention provides equipment at the terminal station for suppressing echo and singing currents which is arranged to maintain the transmitting line disabled except when transmission is taking place and to disable the transmitting line when signals are being received from the distant terminal. The same equipment may be arranged to perform the switching operations incidental to the use of privacy mechanism. By providing full echosuppressor equipment at the transmitting station in addition and by connecting the receiving voiceoperated device at the terminal station at a point nearer the radio receiver than the point at which the disabling means is applied to the receiving line by the voice-operated device in the transmitting line at the terminal station, the " lock-out" period is limited to the time of transmission of the signals through the ether and from the receiver to the adjacent transmitter over the wire line connecting them. The terminal station, Fig. 1, is connected to the transmitting station by a fourwire line TL2, RL2, Figs. 1 and 2, and further lines XL3, RL3, connect the transmitting station to the receiving station. Received signals from aerial AR and radio receiver RR proceed to the line L over lines RL3, RL2, RL1<1>, through the privacy mechanism PM, lines RL1<11>, RL1 and hybrid transformer 10, while signals from the line L to be transmitted through the transmitter TT and aerial AT pass through transformer 10, line TL1' privacy mechanism PM and lines TL1<1>, TL2. The amplifier-detector TAD, bridged across the circuit TL1' controls a master relay TM1 which controls switching relays TSS1, TSS1<1> whose contacts normally disable the transmitting path, and echo hangover relays TEHO1, TEHO1<1> whose contacts when open disable the receiving path. The relay TM1 also controls voice hangover relay TVHO1 which gives the other relays a desired hangover, the TSS relays being released simultaneously with TVHO1, and the TEHO relays being slow to release and hence having an additional hangover. The privacy mechanism PM is common to both transmitting and receiving paths and the TSS and TEHO relays also provide switching for associating this mechanism with the line in use. Thus paths TL1, TL1<1> are normally short-circuited by the TSS relays in their released position, while the contacts of the TEHO relays which are normally closed render the balanced transformers between lines RL2, RL1<1> and RL1<11>, RL1 conductive and connect the mechanism PM in the receiving line. When the relay TM1 is actuated by transmitting currents this state of affairs is reversed, and the mechanism PM is arranged in the transmitting line. The amplifier-detector RAD1 which is bridged either across the line RL1 by connections X1<1> or across the line RL2 by connections Y1<1>, operates a master relay RM1, con. trolling an echo hangover relay REHO1 which on energization opens the circuit of relay TM1 and thereby disables the transmitting line. Delay circuits TD1, RD1 delay the voice currents in the transmitting and receiving circuits respectively until the switching operations initiated by voiceoperated mechanisms TAD1, RAD1 respectively are completed. Volume controls TVC1, RVC1, volume indicators TVI1, RVI1, and amplifiers TA1' TA1<1> and RA1, RA1<1>, are provided in the transmitting and receiving lines respectively at the terminal station, and if transmitting and receiving aerials are widely spaced, the X1<1> wiring may be used for the amplifier-detector RAD1. When, according to the present invention, the transmitting and receiving aerials are close together, the transmitter TT is normally shortcircuited by the contacts of a relay TSS2, the short-circuit being removed when voice currents from the line TL2 operate a further amplifierdetector TAD2 bridged across it by wiring X2 and whose output is applied to relay TSS2 over the wire X2<1>- A delay circuit TD2 holds up the telephone currents until after the operation of TSS2. A manual or automatic volume control TVC2, and indicator TVI2 are provided at the transmitting station and in some cases TD2 may be omitted. The relay TEHO2 is operated by an extra contact on relay TSS2 and prevents currents passing through a transformer between the receiving lines RL3, RL2, while a further contact on TSS2 may operate a relay R3 over an auxiliary line XL3, which in turn energizes a relay TEHO3 over connection Y3 to prevent transmission between the radio receiver RR and the line RL3 in a similar manner. Relay TEHO3 may have an additional contact to disconnect the aerial AR from the receiver RR over wires X3<11>. A delay circuit RD3 is provided so that voice currents from the receiver are held up until relay TEHO3 has operated. Where the line XL3 is long the delay needed may be considerable, so that relay TEHO3 may be arranged to be operated by the currents received by aerial AR by means of an amplifier-detector TAD3 shunted across the receiver RR by wires Y3<1> and whose output is connected to the relay TEHO3 over wire X3. In this case the leads X3<11> are permanently short-circuited by a wire Y3<11>. Alternatively, by operating the amplifier-detector TAD3 over wires X3<1> from an auxiliary radio receiver RR<1>, connected to an aerialAR<1>, which is made directive as regards the transmitter AT, the delay circuit RD3 may be omitted, and the wiring X3<11> restored to the aerial circuit AR. In order to reduce lock-out time to a minimum the winding of relay TSS2 at the transmitter instead of being connected directly to battery over the wire X2<11> is taken through wire Y2<11> through the contacts of a relay REHO2 which open when the relay is energized from the voice-operated amplifier-detector RAD2 provided across the line RL2 at the transmitting station, and amplifier-detector RAD1 at the terminal station is connected by wires Y1<1 >across the line RL2, a delay circuit RD1<1> being introduced between lines RL2, RL1<1>. Pilot waves may be transmitted over the line TL., when ordinary transmission is not in progress to enable the volume control TVC2 at the transmitter to be maintained at its correct position. For this purpose relay TSS1<1> may be arranged to short-circuit oscillators O, O<1>, normally producing frequencies f1, f2 in the line TL2, over wires Y1, when it is energized by the operation of relay TM1 by speech currents, and at the transmitting station, filters F1, F2 and amplifier-detectors TAD2<1>, TAD2<11> connected across TL2 by wires Y2, keep relays R2<1>, R2<11> energized, and thereby also relay R2 which now controls relay TSS2 over wire Y2<1>. When speech currents commence and frequencies f1, f2 cease TSS2 becomes energized by the back contact of relay R2.