Electromagnetic Interference

As hi-fi equipment becomes much sophisticated and complex, the circuits seem to be becoming more susceptible to interference from the outside sources. If a radio transmitter can be operated near a stereo system, the radio signals can be intercepted by hi-fi wiring and peripherals, and delivered to amplifier. Unshielded interconnecting cables behave as radio receiving antennas. This problem is exacerbated if any of the connecting cables happen to resonate at the operating frequency of the radio transmitter. In the amplifier, the RF currents can be rectified, causing changes in audio gain. At times the signal data can be heard in speakers or headset. This is called as electromagnetic interference (EMI).

In most of the cases when EMI takes place in a hi-fi setup, fault exists in the stereo system design, not in radio transmitter. The transmitter system is doing its own job: generating and radiating electromagnetic signals. There are many steps which can be taken while installing the stereo hi-fi system to minimize the likelihood which EMI will occur. These precautions must be followed:

• Connect stereo amplifier chassis to good electrical ground.
• Use the shielded interconnecting cables as much as possible.
• Use the shielded (coaxial) speaker cables.
• Keep all the cables as short as possible.

If you have an amateur or citizens’ band (called as CB) radio station in your house and it causes EMI to your hi-fi system, 2 more steps might be necessary:

• Locate radio transmitting antenna as far from hi-fi equipment as possible.
• Use lowest possible transmitter output power which will ensure the reliable communications.

If EMI problems continue even after all above steps have been taken, a professional engineer may be able to help. If radio transmitter is not always in use (a CB or amateur station, for instance), efforts should be made to avoid using both radio and hi-fi at same time