BS EN IEC 61938:2018 pdf free download Multimedia systems – Guide to the recommended characteristics of analogue interfaces to achieve interoperability (GMT)
6.1.2.4 Magnetic and electromagnetic interference susceptibility of interconnections
The use of untwisted pairs or single conductors with separate return paths is a common source of magnetic and electromagnetic interference at both audio and radio frequencies, especially for loudspeaker wiring, and should be avoided. A description of the methods of avoiding such interference is given in Annex A.
6.1.2.5 Reactance of conductors
The acceptable values vary too widely to give more than general guidance. The cable should not appreciably affect the signal being carried. In the absence of particular requirements, the inductive reactance of the cable should not cause more than 1 d B change in response over the frequency range of interest. The capacitive reactance between the two conductors of a signal-carrying pair, or a coaxial cable, in parallel with the load impedance, should be greater than the rated load impedance, at the highest frequency of interest.
While it is not recommended to use cables in which single conductors carry different audio signals, the capacitive reactance between conductors in this case should exceed 1 000 times the load impedance at the highest frequency of interest.
6.1.2.6 Capacitance from conductor to screen
The acceptable value varies too widely to give more than general guidance. In the absence of particular requirements, the capacitive reactance of a coaxial cable, in parallel with the load impedance, should be greater than the rated load impedance. The capacitance between each conductor of a balanced pair and its screen should be equal within 7,5 %. A closer tolerance is desirable.
NOTE The 7,5 % tolerance, which can be achieved using normal cable manufacturing methods, ensures preservation of adequate common mode rejection in balanced circuits (see Whitlock, JAES, 1 995-06). The electromagnetic interference rejection of such circuits is dependent on impedance balance.
6.1.2.7 Characteristic impedance
This is usually only important for high-frequency signals (such as digital signals in accordance with IEC 60958).
6.1.2.8 Continuity of screening
In some applications, the screen is connected to contacts of connectors at both ends of the cable. In other cases, the screen is connected at one end of the cable only. When the screen of a balanced cable is interrupted, for example to prevent the flow of circulating currents, such interruption should be at the receiving end of the signal path. The screen of a coaxial cable should not be interrupted. Connections between equipment should comply with the requirements of AES48.
BS EN IEC 61938:2018 pdf free download
