# Transmitter interference

### Explanation of question 12

The risk of mains-borne interference may be reduced by using

1. the house mains earth to dissipate any RF
2. an earth leakage trip
3. an external high-resistance RF earth
4. an external low-resistance RF earth

The answer is :- 4 An r.f. earth connection to the house mains earth can induce r.f. into the mains supply, which can cause interference to audio and visual equipment. More important, it could be the cause of a breakdown of insulation resistance of the house wiring. Water supply systems are very suspect and should be avoided for an r.f. earth connection. A connection to an external earth spike by a short length, i.e. low resistance, of wire is the optimum solution.

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