The screening of CATV cable assemblies: proposed test methods with results for frequencies from 0.1 MHz to 1 GHz

Because of the need for improved screening on TV connectors which are used widely for connecting a TV set to its antenna and video recorder, an IEC specification has been prepared which includes details of screening attenuation. The specification is not yet published but will have the title IEC 60966-2-4: Radio frequency and coaxial cable assemblies-Part 2-4: Detail specification for cable assemblies for radio and TV receivers. The screening attenuation specified has a maximum value of 75 dB up to 1 GHz and 55 dB up to 3 GHz. There is some argument as to how this should be derived for a cable assembly, so a way round the problem is given here, where the screening attenuation is derived from individual measurements of transfer impedance (Z_T) on the connectors and cable of the cable assembly. It is also proposed that these measurements can usefully be carried out at frequencies below 100 MHz. Measuring methods, one for frequencies up to 1 GHz, and another limited to about 100 MHz, are first described. Their use is demonstrated with a variety of TV cable assemblies and connectors bought on the retail market. Finally an approximate way of converting the Z_T measurements to a_s (screening attenuation) values is used. It is of interest that only one of the cable assemblies tested showed any probability of meeting the limit of the IEC specification