GB728584A - Improvements in testing arrangements for wide-band telecommunication systems - Google Patents

Abstract

728,584. Unattended repeaters. BRITISH TELECOMMUNICATIONS RESEARCH, Ltd. May 12, 1952 [May 23, 1951], No. 12098/51. Class 40 (4). In an arrangement for testing unattended repeaters along a four-wire multiplex transmission route, the inputs and outputs respectively of the " go " and " return " amplifiers at each station are connected by filters F2, F4 in order that a signal such as the intermodulation products of two tones transmitted from a terminal station for testing purposes may be returned thereto. Series filters F1, F3, Fig. 1, which have a stop-band falling within the passband of the cross-connecting filters, suppress distortion products from the preceding stages. Test tones A and B are transmitted and second or third order difference frequencies are returned, and by variation of A frequency, B frequency, or both successive tests of successive repeaters may be made. A loop loss test may also be made with a frequency lying in the passband F2 of each station but outside of the blocking filters F1 and, F3. Test tones and their intermodulation products are selected to lie in the interchannel gaps in order that testing may be effected without interference with the system. The filters F2, F4 have a low bridging loss and may be switched into or out of circuit with the minimum of disturbance.