Electromagnetic Interference

As hi-fi equipment becomes more sophisticated and complex, the circuits become more susceptible to interference from outside sources, particularly electromagnetic (EM) fields. This problem is known as electromagnetic interference (EMI). Sometimes it is called radio-frequency interference (RFI).
If a radio transmitter is operated near a hi-fi stereo system, the radio signals can be intercepted by the hi-fi wiring and peripherals, and delivered to the amplifier. Unshielded interconnecting cables act 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 hi-fi amplifier, the RF currents are rectified, causing changes in the audio gain. Sometimes the signal data can be heard in the speakers or headset.
In most cases when EMI takes place in a hi-fi setup, the fault exists in the stereo system design, not in the radio transmitter. The transmitter system is merely doing its job: generating and radiating electromagnetic signals!
Several steps can be taken when installing a stereo hi-fi system to minimize the likelihood that EMI will occur:

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

If you have an amateur or citizens band (CB) radio station in your house and it causes EMI to your hi-fi system, perform these additional steps:

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

Unfortunately, EMI problems can sometimes prove nigh impossible to eliminate. This can be especially troublesome for amateur and CB radio operators when it damages relations with neighbors. In these cases, old-fashioned diplomacy may work better than engineering-based attempts at resolution.