| 摘要 |
<p>970,736. Testing repeaters in pulse communication systems. WESTERN ELECTRIC CO. Inc. Nov. 29, 1961 [Dec. 20, 1960], No. 42787/61. Heading H4L. Relates to a system for detecting a faulty repeater in a chain of pulse regenerative repeaters and is particularly applicable to bipolar pulse code communication systems in which normally there is only a small direct current component. A test signal consisting of pulse groups in which there are more pulses of one polarity than the other and thus having a direct current component, and having a group repetition frequency which is adjustable and is substantially less than the pulse repetition frequency of the system is generated at the transmitting terminal and each repeater is provided with a filter responsive to a frequency indicative of that repeater. The pulse density of the test signal, and hence the D.C. component, is varied, and the response of the repeater is transmitted back via a return path to indicate the condition of the repeater. In a typical test signal, Fig. 3, line a shows an arrangement of unipolar pulses to provide the D.C. component, line b shows a succession of pulses of alternating polarity combined with the test signal as at c in order to clock the repeaters, and line d shows the " identification tone " resulting from the grouping of the unipolar pulses and having a frequency equal to the group repetition frequency. The test signal is generated at 12, Fig. 4, and applied to the input terminals of the system comprising repeaters 14, 16, 18, 20, 22, each repeater being equipped with a filter 24 to 32, respectively, responding to a frequency f 1 to f 5 peculiar to that repeater. In operation, the repetition rate of the unipolar pulse groups is adjusted to correspond with the frequency allotted to the repeater under test, the test being started with only a small number of unipolar pulses per group which are gradually increased by predetermined amounts to increase the amplitude of the identification tone, with corresponding increase of the D.C. component, until a point is reached at which the amplitude of the identification tone as measured at 13 shows a sharp fall, Fig. 5 (not shown). This gives a measure of the quality of the transmission. A generator for the test signal is described, Fig. 6 (not shown), in which a unipolar pulse train whose density may be varied is first generated and is gated on and off at the required identification tone frequency.</p> |
