Ground o

Neutral O

Neutral O

14-3 (A) Ac line EMI filter and (B) power cord on ferrite rod also reduces EMI by acting as a RF choke.

Other interference 291

coming from the offending device. It works much of die time because the principal source of the noise signal is radiation from the power line of the VCR or TV, The EMI mter should be installed as close as possible to the body of the'offending device.

The filter in Fig. 14-3A uses LC elements to form a low-pass filter network that is placed in series with the ac power iine. Homebrew filters should be built inside of a quality, heavy-duty, shielded metal box. If you make your own filter, be sure to use capacitors and inductors that are rated for continuous use across ac power lines. Most readers should consider buying a ready-made LC line filter from a distributor (even RadioShack offers models suitable for most applications). Homebrew EMI filters have a potential for danger if built incorrectly—they can electrocute you or cause a fire in your house!

The filter shown in Fig. 14-3B can be made for any appliance that uses ordinary zipcord for the power line. The cord is wrapped around a to ferrite rod (Ami-don Associates), which is then taped to keep it in place. This filter should be mounted as close as possible to the TV or VCR chassis. The optional bypass capacitors (Ci and C3) inside the equipment cabinet should be 0,01-p.F 1600-WVdc disk ceramics that are lated for continuous ac service.

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