| 摘要 |
A porcelain (14, 27, 35, 58) coated metal substrate (13, 26, 57) bearing a printed circuit (11, 28, 31, 32, 33, 36, 62) and in which a capacitance effect is created between the substrate (13, 26, 57) and the circuit to eliminate unwanted frequencies. The capacitor may be formed by having a ground connection (15, 40, 64) to the metal substrate or by providing a further capacitance from the substrate to another conductive member which is itself ground. The invention is of particular use for audio equipment, e.g. a pushbutton switch for telecommunications equipment in which high frequency signals are to be eliminated.
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