BS 50083-8:2002 pdf download – Cable networks for television signals, sound signals and interactive services — Part 8: Electromagnetic compatibility for networks
NOTE Only the abbreviations used in the English version of this part of EN 50083 are mentioned in this subclause.The German and the French versions of this part may use other abbreviations.Refer to 3.3 of each language
versions for details.
4Methods of measurement
These methods of measurement describe the procedures for the testing of cable networks. The purposeof the measurements is to determine:
. the level of radiation generated by cable networks and
.the immunity of cable networks to external field strengths (e.g. those radiated by other radiocommunication services and RF applications).
The measurements cover the essential parameters and environmental conditions in order to assess:
cases of electromagnetic incompatibility between cable networks and other electrical or electronicequipment, networks, installations or other cabled networks with respect to the intended operation ofsuch cable networks.
During the test the cable network shall operate with normal signal levels at the subscriber outlets. If thestream is interactive, typical levels of the return path signals shall be maintained during the test.
NOTE Methods of measurement for digitally modulated signals are under consideration.
4.1 Radiation from cable networks
The methods described hereafter are applicable to the measurement of radiation from cable networks(combination of cables, equipment and networks).
Testing of the cable networks for compliance with the relevant limits may be initially carried out with theterminal equipment connected. Where limits are exceeded, individual sections of the network (e.g.
headend, satellite receiving outdoor unit, cable network, distribution installation beyond the system outletsand terminal equipment) may be tested in succession to determine beyond any doubt which section of thenetwork does not comply with the limits.
The number of test frequencies shall be selected to give a realistic representation of the radiation patternthroughout the operating frequency range and to enable the maximum level of radiation to be recordedand the results interpreted accurately.
The field strength measurement procedure is used in order to achieve results which are sufficientlyaccurate and do not require excessive technical effort.
The substitution measurement technique is applied to carry out more accurate measurements of theradiated disturbance power level generated by any part of the network.
lf discussions arise about the actual radiation from a cable network, the substitution method according to4.1.2 has to be applied.
The maximum permitted radiation level is given in 5.1, Table 1.
The following problems can cause radiation from cable networks:
poor or faulty screening of passive equipment (plugs, splitters, etc.);
poor or faulty screening of active equipment (amplifiers, converters, etc.);
poor or faulty screening of the distribution cables against induced voltages;
excessive impedance in the ground connections of the input terminals of active and passive equipment;
insufficient rejection of power supply borne interference on mains powered equiment;
inadequate mounting of connectors on cables;
damage of the screening of cables or connectors.
4.1.1 Field strength method
The field strength method uses a suitable magnetic loop antenna in the frequency range from 5 MHz to 30 MHz and a suitable electromagnetic field antenna in the frequency range 30 MHz to 950 MHz.
Usually a loop antenna is conventionally calibrated in terms of “equivalent electric component” of the electromagnetic field. If a loop antenna calibrated in terms of magnetic field is used, the level of the equivalent electric field is deduced from the level of the measured magnetic field according to the following formula:
E is the equivalent electric field level in dB( ? V/m)
H is the measured magnetic field level in dB( ? A/m)
51,5 = 20 lg(120 ? ) is the free space impedance in dB( ? ). Equipment required
The equipment required for the measurement of the radiation from a network is listed below:
a suitable spectrum analyser (battery powered) with a digital recorder or a plotter;
The spectrum analyser should cover the frequencies distributed within the network with a resolution bandwidth (IF bandwidth) according to CISPR 16 (see Table 1) and an appropriate slow sweep speed.