| 摘要 |
In order to test the line and the equaliser stations (1, 2), disposed at intervals, of a four-wire PCM transmission system, each individual equaliser station is polled by means of a specific PCM signal. This signal contains a number of bits with single-bipolar deviation from the HDB3 code, which number corresponds to the ordinal number of the equaliser, and is transmitted into the line between two bits with double-bipolar deviation. The test circuit (F, K) of the polled equaliser station activated in this way connects the line pair at the transmitting end with the line pair at the receiving end so that the return of a test signal transmitted at the end of the line can be observed there. A similar signal is transmitted to cancel the short circuit, the number of bits with single-bipolar deviation, however, being greater than the ordinal number of the equaliser station which has just been tested. <IMAGE>
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