Patent GB-1383699-A (GB)
Title: Information signal transmission system
IPC: H04B17/40
Filed: 1972-04-18
Abstract: 1383699 Supervising unattended repeaters PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 18 April 1972 [21 April 1971 7 Dec 1971] 17861/72 Heading H4R In a supervisory arrangement for unattended repeaters stations of the kind in which each repeater station includes an oscillator which when energized transmits a signal to a terminal station, an oscillator start-stop device associated with each oscillator includes a cascade arrangement of a selective circuit and an amplitude measuring device and operates in such a manner that the oscillator is only energized if a control signal received at the start-stop device from the terminal station has a frequency and an amplitude valve corresponding to the response frequency and amplitude of the selective circuit and amplitude measuring device respectively. General.-Fig. 1, shows such an arrangement applied to a transmission system including separate go and return paths 4, 3 having connected therein repeater stations 5-7, 5<SP>1</SP>-7<SP>1</SP>, respectively the repeater station 6 being shown in more detail. In a practical system there may be up to 40 repeaters in each path. D.C. power is fed to the repeater stations and the speech paths from a power supply 22 situated at a terminal station 1. Each line amplifier 9-11, 14-16 associated with the repeater stations is shunted by a D.C. supply by-pass circuit 23 comprising filters 29, 30 and a Zener diode 24 which is provided both for protecting the line amplifier from large valves of longitudinal currents and for keeping the supply current intact when the D.C. circuit in the line amplifier is interrupted. The supervisory arrangement includes at each repeater station a capacitor 38 shunting the Zener diode, an oscillator 31, and an oscillator start-stop device 32, and at the terminal station 1 a control circuit 33 including a control oscillator 36 and an amplitude control device 37, a switch 35 for coupling a control signal to either of the two speech paths and an indicator 34 for receiving response signals sent from the oscillators at the repeater stations.  The basic operation of the system is as follows. For repeater stations in the transmission path 3 incoming to terminal station 1, a control signal characterized by its amplitude and frequency, which frequency is of a value below the speech transmission band frequency range, is sent from control circuit 33 via switch 35 and filter 25 to the speech path. It then travels along the speech path and at each repeater station bypasses the line amplifier via filter 29, capacitor 38 and filter 30 until it arrives at a repeater station having an oscillator start-stop device 32 which is responsive to the particular amplitude and frequency of the control signal received. The oscillator is then energized and a responsive signal is fed to the input of the corresponding line amplifier and thence back along the speech path either through the line amplifiers or the by-pass circuits to operate the indicator 34 at the terminal station 1. For the outgoing path 4 a similar operation takes place except that the response signal produced by the relevant oscillator is transmitted on to terminal station 2 where it is either selectively coupled to the path 3, e.g. in the case of terminal station 2 being unattended, or it operates an indicator (not shown), at this terminal station. Details of the embodiments.-In a first embodiment, a set of three different control frequencies are used, e.g. 27, 30 and 33 kHz, situated in a frequency range 2-35 kHz, which range is below the speech transmission frequency band of 4 to 60 MHz, and every third repeater station along each path has the selective circuit in the oscillator start-stop device tuned to the same frequency. The oscillators of every repeater station produce the same response frequency signal which comprises a two-tone frequency, one frequency of which lies above the speech transmission frequency band, and the other frequency of which lies below the said band, e.g. a 3À8 MHz and a 63 MHz composite frequency tone may be employed. In order to distinguish between every third repeater use is made of the attenuation of the control signal along the path, the amplitude measuring devices of all the repeater stations are set to respond to the same amplitude level signal, i.e. the oscillator is energized for incoming control signals within a small range of a given value which value is the same for all repeater stations, and the amplitude of the control signal fed to the path is adjusted using a simple potential -divider arrangement (Fig. 2, not shown). With such an arrangement an amplitude change of 3dB is necessary to operate successive repeater station oscillators actuated by the same frequency of control signal (depending on repeater station spacing). With such an arrangement the repeater stations can be made identical and an external connection can determine the control frequency to which the selective circuit responds. Fig. 4, shows an arrangement for coupling the response signal between the outgoing path 4 and incoming path 3 at the terminal station 2. Filters 70, 71 select the frequencies 3À8 MHz and 63 MHz respectively, which are then amplified by amplifiers 72, 73 before being fed to the transmission path 3. The control signals of 27 and 30 kHz may be used to switch on the amplifiers 72, 73, these signals being transmitted with a larger amplitude than is required to activate the oscillator start-stop device for the last repeater station. The control signal frequency of 33 kHz is similarly used to switch off the amplifiers 72, 73.  A second embodiment described with respect to Figs. 5 and 6 (not shown), uses a single variable amplitude control frequency signal and the repeater stations are arranged in groups of ten, each of the stations in the group of ten having oscillators producing mutually different response frequencies. As in the first empbdiment the amplitude measuring devices of the stations are all operative for the asme amplitude of received control signal. Such as arrangement may be used when up to 80 repeater stations are positioned along a 120 km. transmission path. At the terminal station an indicator comprising a plurality of incandescent lamps is used (Fig. 6, not shown). By applying a gradually increasing control signal the lamps are lit up and extinguished repetitively as each group of ten repeater stations is tested. In order to tell which groups have been tested the tenth repeater station of each group may have an oscillator frequency which is different from all the other oscillator frequencies and the oscillator startstop device associated therewith may be characterized in that once the control signal exceeds a threshold level the oscillator remains operative and does not switch-off as the level of the control signal further increases. Hence after each successive group of ten repeater stations is tested by increasing the control signal amplitude a light representive of the group is lit and remains lit. The different response frequencies of the oscillators may be single frequency or double frequency tones employing frequencies outside the speech transmission band. The control signal frequency may be 3À5 kHz.