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Transmit Power Levels and the FCC

NC-Dave

New member
Radio transmitters and transceivers are categorized by the FCC here in the USA as "Intentional Radiators". Any such radio device is regulated as to it's maximum power level and it's transmitted harmonics. Even a radio receiver has to pass a very stringent set of tests to make sure that it does not radiate unwanted energy. Receiver's usually radiate some energy from their conversion oscillators and can be harder to get through their compliance testing than a transmitter.

Metal detectors are not intentional radiators. They do not come under the same rules as radio's. Most metal detectors operate at audio frequencies. Stereo loudspeakers also transmit some of their signal through the air They too do not require RF compliance testing.

The coil size required to efficiently transmit a signal at metal detector frequencies would be incredibly large. Antennas are made in wavelengths or fractions of a wavelength such as a quarter or a half wavelength.

The wavelength in meters = 300,000,000/frequency in Hz. OK, so for a metal detector operating at 5000Hz (5KHz) the the wavelength is 60,000 meters. A half wave antenna would be 30,000 meters from end to end. That is 18.64 miles while a nice little quarter wave mobile whip would extend to just over nine miles above your car. You can now see why your ten inch loop is not going to cause too much of a problem.
 
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