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AM RADIO AS INEXPENSIVE HIGH FREQUENCY SENSOR


by Richard Conrad, Ph.D., updated 6/19/10

Most gaussmeters (magnetic field meters) are designed primarily to measure 60 cycle magnetic fields from house wiring. They usually are not accurate at higher frequencies, and are largely insensitive to frequencies in the Megahertz and Gigahertz range, where most monitors and computers have much of their emissions. A useful, inexpensive ($99. from Frys Electronics on line, the last I looked) milligauss meter for measuring magnetic fields from house wiring and power lines is the standard analog TRIFIELD meter by AlphaLab (their least expensive model: Trifield Meter 100XE). It is very helpful that a gaussmeter measure all three field directions simultaneously, as the Trifield does. For more on gaussmeters, and for an EXPLANATION OF TERMS such as gauss, cycles, frequencies, MegaHertz, KiloHertz, etc. see the article: GAUSSMETERS.

FOR HIGH FREQUENCY SENSING:
An inexpensive battery-powered AM radio can be used as a crude but very useful sleuthing tool for high frequency EMF emission sensing by carrying it around to different locations, and by bringing it near electrical devices such as components of computer systems, etc. Set the frequency dial all the way to either the low end or the high end, where it is not receiving a radio station (the lower end works best for some but not all EMF sources). Each electronic device will cause a characteristic sound from the speaker, and the maximum distance away from the device that the radio still produces the characteristic sound gives a rough measure of intensity of the high frequency emissions. If the sound disappears at two inches away, the source is not a strong one. Six inches is moderate strength, one foot is strong, three feet is very strong. A very strong source, even though not audible beyond three feet, can still effect an electrically sensitive person at a distance of twenty feet or more. The AM radio can be a great help by making some EMF emissions audible, but note that some devices can affect a sensitive person even when (or at distances at which) the AM radio is silent, and conversely, sometimes the sound from the radio can be loud and yet the device may not affect a person because the frequency of the EMF does not match their sensitivity range, which is different for different people. Sensitive people might want to tape the radio to the end of a yardstick, etc., so that they don't have to get their hand close to the source, and so that they avoid being affected by the magnetic field that the radio's speaker produces when it makes sound.

The AM radio can pick up emissions from a dimmer switch, fluorescent lamp (compact or otherwise) or switching power supply, not just within a few feet of the device, but also anywhere in the house, because the emissions are conducted on the house wiring and are then emitted from the wiring throughout the house.

It is important to know that bringing the radio to within a few inches of any large or long metallic object can increase the volume of the background static - this occurs via an inductive coupling of the internal ferrite antenna to the metal object which effectively increases the gain of the radio's antenna. This is an artifact, and does not indicate that the metal object is attracting, concentrating or emitting high frequency energy. Nor does it indicate that a person close to the metal object is being exposed to high frequency emissions. Most electronic devices cause a unique characteristic sound that is distinguishable from background static.

The best (the most sensitive as a non-specific high frequency sensor) AM radio that I have found for this purpose is the Radio Shack AM/FM POCKET RADIO, CAT. NO. 12-586, and it costs only $14 on their website. (This model is almost identical to and replaces the discontinued Radio Shack CAT. NO. 12-467, and performs the same). Other/similar Radio Shack models and most other brands of AM radios are not nearly as good for this purpose because their tuners are more selective. (For our purpose here we want a tuner with poor selectivity). Use the radio on the AM setting, and there is no need to extend the telescoping antenna because that antenna is for FM; the AM antenna is a directional ferrite rod that is inside the top of the housing.