Patent GB-1068890-A (GB)
Title: Improvements in or relating to carrier-wave telephone systems
IPC: H04B17/40
Filed: 1964-12-07
Abstract: 1,068,890. Supervising repeaters; keying carrier frequencies; transistor switching circuits; transistor oscillator circuits. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. Dec. 7, 1964 [Dec. 10, 1963], No. 49610/64. Headings H3R, H3T and H4R. A carrier-wave telephone system (Fig. 1) includes West station WS, East station ES and a plurality of repeater stations of which only stations VS1 and VS2 are shown. Each station includes a W-E line repeater A, an E-W line repeater B and a measuring oscillator C. The signal output of each oscillator C is connected through resistance decoupling networks DA and DB, respectively, to the inputs of repeaters A and B belonging to the same station. The measuring signal applied to the E-W line repeater is directly transmitted in the W direction through line 2 to the main station WS and is separated therein from the remaining signals by a filter 7 and applied through a rectifying circuit 8 to a D.C. voltmeter 9. The measuring signal applied to the input of the W-E line repeater A is first transmitted in the E direction through line 1 to final station ES. The measuring signal is separated from the remaining signals by a filter 10 and, after amplification by amplifier 11, is applied to the input of repeater B4 and transmitted to station WS through line 2. Two measuring signals of different levels are thus received in the final station WS since the measuring signal originating from repeater A has, due to amplifier 11, a higher level than the signal originating from repeater B. A defective repeater may be localized by switching on the oscillators C in succession, beginning with the oscillator in main station WS, each oscillator being switched off before a subsequent oscillator is switched on. If, for example, repeater A3 is defective a low level signal is received in station WS after switching on oscillator C3 and until a measuring signal of high level is received after switching on oscillator C4. If, however, repeater B3 is defective a measuring signal of low level is received in station WS after switching on oscillator C2 and no measuring signal at all is received after switching on oscillator C3. From these indications on voltmeter 9 it is possible to localize a defective repeater. The oscillators C1 to C4 are in parallel and are connected to the two wires of a. control line 12 which is connected in station WS through a reversing switch 13 to an adjustable direct voltage source 14. In each station the wires of the control line are through-connected in a cross-wise manner so that diodes E with even numbers or those with odd numbers are conducting dependent on the polarity of the voltage between the wires of the control line 12. As illustrated. upon raising the voltage of the source 14 only the oscillators C1, C3 with odd numbers become successively operative, whereas in the opposite position of switch 13 only the oscillators C2, C4 with even numbers can be successively switched on. Resistors RA, RB in the control line 12 are so proportioned that the input resistance of the line 12 at the position of an oscillator C n  in the direction of the current associated with this oscillator C n  is invariably equal to a terminating resistor RL. Measuring oscillators.-An oscillatory circuit is constituted by a coil 19 (Fig. 2) and capacitors 20, 21. The common point of capacitors 20, 21 is connected to the emitter of a transistor 15 for back-coupling the oscillatory circuit. An output coil 22 is provided. Transistor 15 forms, with a transistor 32, a Schmitt trigger whereby the conductivity state of transistor 32 is opposite to that of transistor 15, switching from one state to the other being effected as soon as a switching voltage is applied to the base of transistor 32. Voltage dividers 34, 35 and 28, 37 are provided and are so proportioned that a transistor 36 is conducting upon raising a supply voltage, applied at terminals a, b, to a certain level. At this voltage a Zener diode 25 breaks down and the emitter voltage of transistor 36 remains constant upon a further increase of supply voltage. As the supply voltage increases further, transistor 36 cuts off. A voltage divider 38, 39 is proportioned so that, as soon as transistor 36 is cut off, two transistors 40, 42 become conducting in series. The collector circuit of transistor 42 includes a resistor 33 and the voltage drop set up across this resistor cuts off transistor 32 so that transistor 15 is operative and the oscillator also becomes operative. The oscillator becomes operative at the breakdown voltage of Zener diode 25 so that the oscillator works at an accurately determined frequency. When the supply voltage is raised further the voltage on the base of transistor 42 decreases with respect to the emitter and transistor 40 is cut off. This results in transistor 32 becoming conducting and hence transistor 15 is cut off and the oscillator is made inoperative. Diodes 43, 44 prevent undue cut-off voltages appearing across the emitters of transistors 36, 40. Compensating diodes 26, 27 compensate for temperature variation in the emitter-base voltages of transistors 36, 40 and for temperature variation in the breakdown voltage of Zener diode 25.