DATA TRANSMISSION BY MEANS OF RAILWAY TELEPHONE CIRCUITS AT SPEEDS EXCEEDING 600 BAUDS. INFLUENCE OF THE WESTERN ELECTRIC DISPATCHING SYSTEM AND OF MOTIVE POWER UNITS WITH "THYRISTOR" FIRING-ANGLE CONTROL OF TELEPHONE CIRCUITS INTENDED FOR DATA TRANSMISSION
Part 1 of this report contains a description of the composition and layout of the Western Electric dispatching system and of its influence on data transmission circuits, established on the basis of measurements made by the SNCF. Part 2 of the report deals with the influence exerted by motive power units with thyristor firing-angle control (thyristor-control led locomotives) on data transmission circuits. The results of the measurements with the Western Electric dispatching system show the following: Different modulation procedures are used. (Particular mention is made of the transmission systems with d.c. and those with a.c. (50 Hz) Data transmission is unfavourably influenced by both procedures. Disturbance voltage peaks of the order of 50 mV are produced in the data circuits by the calling-pulses of the dispatcher system. Those carrier-channels situated close to the audio-frequency band are the most strongly disturbed. As the lowest permissible signal voltage of the data transmission system is about 8 mV for the audio-frequency circuits and about 18 mV for the carrier frequency circuits, the disturbance voltage peaks should not exceed 2 mV for the audio-frequency and 4 mV for the carrier frequency circuits (at the point of relative zero level). The disturbances produced by the calling-pulse can be reduced by modifying the circuit-switching arrangement. For orientation purposes, the Committee has carried out measurements on the SNCF concerning the disturbance-voltages produced by the operation of thyristor controlled locomotives. Results: Thyristor-controlled locomotives constitute an important source of interference. According to recommendation G 123 of the CCITT (Internationa Telegraph and Telephone Consultative Committee), only values of 0.5 mV (effective value, A-filter network) are permissible for the disturbances produced in conductors by high-voltage circuits. This applies to a circuit terminated with a characteristics impedance. In the other hand, the appearance of disturbance voltages of up to 15 mV have been observed. The maximum disturbance voltage peak was 47 mV. It follows from this that the effective disturbance voltages are higher by a factor of 30 than those permissible.
- Restrictions on the use of this document are contained in the explanatory material.
International Union of RailwaysOffice of Research and Experiments
- Publication Date: 1970-4
- Features: Figures;
- Pagination: 101 p.
- TRT Terms: Communications; Data communications; Electric locomotives; Frequency modulation; Interference; Telephone equipment; Thyristors
- Old TRIS Terms: Question a76; Thyristor control
- Subject Areas: Railroads; Vehicles and Equipment;
- Accession Number: 00052707
- Record Type: Publication
- Source Agency: International Union of Railways
- Report/Paper Numbers: A76/RP 8/E
- Contract Numbers: D-5041
- Files: TRIS
- Created Date: Apr 21 1979 12:00AM