| 摘要 |
<p>1391364 Testing unattended repeaters TELECOMMUNICATIONS RADIOELECTRIQUES ET TELEPHONIQUES 21 June 1972 [24 June 1971] 29033/72 Heading H4R In an arrangement for testing the repeaters of a transmission system by looping back between the go and return paths successively at each repeater station along the system, the looping back is effected in response to a supply polarity reversal and each repeater station contains a memory circuit which allows the repeater station to respond to the first polarity reversal and effect looping back, but to ignore subsequent reversals to allow successive stations along the line to respond. As described in respect to Fig. 1, which is for a system where repeater power is derived, via a bridge rectifier circuit 28, from across the phantom formed by the go and return circuits, a polarity reversal by operation of switch 25 at terminal station 1 causes, via diode 32, the conduction of transistor 31 and operation of relay 22 in repeater 5. Operation of relay 22 causes looping back of the go and return paths at contacts 23, breaking of the incoming return path at contacts 39, 40, and charging of capacitor 36 at contacts 38. Subsequent restoration of normal supply polarity releases relay 22 causing capacitor 36 to fire thyristor 35. A subsequent reversal of polarity has no effect on transistor 31, since thyristor 35 remains conductive until there is a substantial supply interruption, and so the polarity reversal is allowed to pass to the next repeater, to effect looping back there. After all the repeaters have been tested by looping back in turn, further polarity reversals may be used to effect testing of subscribers lines connected from the terminal station 2. An alternative arrangement, Fig. 2 (not shown), is described for a system where repeater power is derived from across oppositely poled Zener diodes in series in the supply lines.</p> |
