At present, sources of interfering electrical noise in a facility must be detected using a time-consuming trial-and-error approach. It is expensive because resolving such problems is often performed by independent electrical noise consultants contracted on a daily basis. Current techniques for detecting and determining the direction of EM signal sources generally involve the use of large and unwieldy directional antennas having diameters of many meters or the use of antenna arrays. In practice, the large size of a directional antenna renders impractical obtaining the source direction from very low-frequency signals (hertz to kilohertz range) such as the electrical noise harmonics that commonly emanate from the power supplies of electronic systems.

In addition, common antennas and receivers for detecting EM signals are usually designed only to capture the electric-field component of the signal. Since electromagnetic waves are characterized by both electric and magnetic field potentially significant information is lost.


The LLNL approach uses both the electric and magnetic components of an electromagnetic wave, which provides information about the direction of wave emanation as well as the flux of energy in the wave. This new, potentially portable technology is intended to identify and locate low-frequency electromagnetic noise sources in order to take off-line or quickly isolate and repair the interfering electrical/electronic equipment operating in buildings, factories and large commercial facilities. The technology will also have application relating to locating general EM signal sources having frequencies falling within the operational bandwidth of the receiver.


  • Directionality can be readily determined
  • Potentially highly portable
  • Diagnostic tool rather than trial and error method
  • Locate lower frequency (e.g., power-line frequency and associated harmonics) electrical interference noise sources in complex electrical/electronic environments.
  • Locate non-noise sources that have frequency components falling within the operational bandwidth of the receiver.
Potential Applications

Electrical noise detection and elimination as well as non-noise signal location has commercial, law enforcement and military applications

Specifically, the features and benefits to the applications are listed below.

The ability to measure both the electric and magnetic field of an electromagnetic wave does not require the antenna size to be comparable to the wavelength of the signal being acquired and makes possible low frequency noise directionality applications and portability.

The technique allows the separation and identification of different frequency sources through signal analysis so that the direction of signals that even overlap in frequency can be isolated from each other.

The antennas are omni-directional allowing:

  • All signals in a given frequency range to be captured
  • Intermittent noise or signals of interest are not missed as is the case when using directional antennas pointed in the wrong direction.
  • Moving sources can be tracked without re-orienting the receiver.

Directionality can be obtained entirely through the analysis of acquired signal and not by a hands-on re-orienting of an antenna during signal acquisition. This allows signal direction to be obtained either in real time or by post-processing of saved digital signal data and the passive acquisition of data in remote environments without human involvement.

Development Status

Initial field testing has identified noise signals from a power generator and load providing directional information about the noise source. These tests have made apparent the advantages of measuring both the electric and magnetic fields of a signal. Further development is needed to scale down the electric- and magnetic-field antennas, the receiver and the processing hardware to a convenient level of portability (e.g., handheld).

The analysis technique has been developed through subsequent detailed computer simulations of noise and signal sources, but is still in development and can benefit from signal processing and optimization development.

The method and apparatus described is described in US Patent 7,440,858.

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