IN PRACTICE

摘要

You need to think about internal EMC at all levels within a project. Start with the detailed design and layout of individual stages on a PC board, think about the general layout of the whole board and the interconnections between modules, and finish with the interconnections to other equipment in your station. Before you start to design or build anything, you need to identify the types of signals that could be carried by the interconnecting leads. In this context, anything counts as a 'signal', including DC power supplies, mains or low-voltage 50Hz supplies, DC control signals, digital signals and of course the RF, LF and audio signals. The key to EMC control is to realise that none of these interconnections carries a pure signal - there is always some coupling between them. You must plan not only to minimize the coupling but also to minimize the effects of whatever crossover does take place. You can minimize unwanted coupling by careful layout of the individual PC boards and their interconnections. Precautions to minimize the effects of coupling are usually taken on the PC boards themselves.