EMC ( Electro-Magnetic Compatibility )

Learning outcomes from this part

• Know that all electronic equipment is capable of radiating and absorbing radio frequency energy.

• Know that the basic principle of electromagnetic compatibility is that equipments should limit radiation to below a specified level and also be able to withstand a certain level of incident RF radiation.

• Know that the levels of RF radiation are given in the EMC regulations.

• Know that transmitters in domestic environments may give rise to RF fields stronger than the specified limits.

• Know that transmitters in domestic environments are not 'normal' situations and special measures may have to be taken.

• Know  that new electronic equipment should meet the EMC immunity standards but that existing equipment and poorly installed equipment may not.

• Know how to interconnect the transmitter, microphone, power supply, SWR meter and band or low pass filters, using appropriate cables, to minimise EMC problems.

• Know that filters can be fitted in the leads from the power supply to the transmitter to help minimise RF energy entering the mains wiring.

• Know what constitutes a good RF earth, its purpose and use.

• Know how to use a suitable general coverage receiver to check for spurious and harmonic emissions from the station.

• Know that siting a transmitting antenna close to mains wiring, TV or radio aerials and downleads is a potential problem exacerbated by the use of a loft or indoor transmitting antenna.

• Know the forms of interference caused by amateur radio and other radio transmissions: patterning on the TV screen, loss of colour, voice on TV sound, radio, telephone or audio systems.

• Know that interference to digital televisions is different. The picture may freeze, become jerky or disappear.

• Know that other sources of interference and their effects: thermostats and vehicle ignition systems, electric motors in vacuum cleaners, fans, drills, sewing machines etc. Spots on TV or radio sound.

• Know that direct pick-up in affected devices tends to be independent of the transmitted frequency.

• Know that masthead and downlead TV amplifiers are broadband and so they amplify a wide range of frequencies, including amateur frequencies.

• Know that masthead and downlead TV amplifierscan overload the TV input.

• Know that the use of ferrite ring filters for minimizing unwanted RF on aerial downleads and mains leads to affected equipment.

• Know the use of high-pass filters to reduce the level of HF and VHF amateur transmissions into TV systems.

• Know the use of mains filters to reduce RF, electric motor and thermostat interference to TV, radio, and audio systems.

• Know that transmitting into a dummy load is a good test for any unwanted RF being conducted out of the transmitter along its power supply leads and into the mains.

• Know that the station log will be of considerable assistance in confirming sources of interference to neighbours.

• Know the merits of the amateur and the complainant keeping a log of the instances of interference.

• Know the merit of conducting tests in co-operation with the complainant in instances of interference.

• Know the existence of and that advice is available from the RSGB EMC Committee and the role of local RA officers in dealing with cases of interference.

• Know that RA and the RSGB produce information leaflets on EMC and interference.