Localised noise is clearly in the induction or near field region. Wavelengths between 500 and 15,000 meters, and reception of Magnetic components of received field up to distances of oneĪt VLF and LF (10 to 300 kHz) we are concerned with half The effect of all this is that, in the near field, the electricĬomponent is much stronger than the magnetic component. Both the electric and magnetic components of the radiationįield decrease directly with distance and dB = 20log (d2/d1) The square of the distance and dB = 40log (d2/d1)ģ. The magnetic component of the induction field decreases with The cube of the distance and dB = 601og (d2/d1) where d2 and d1 areĢ. The electric component of the induction field decreases with The relationship between field strength and distance isġ. Atĭistances greater than one half wavelength, the radiation field is Wavelength, the induction or near field is prominent but it fallsĪway at a greater rate with distance than the radiation field. To explain this, it is necessary to briefly discuss the fieldsĪround a radiating element. Received signal-to-noise ratio can be improved with the use of a In the presence of this type of noise, the Level of local noise generated from noisy power lines and consumerĮlectrical equipment.
The discussionĮxtends to the problems of amplifier noise and the advantages ofĪ major problem in receiving VLF and LF signals is the high
A Loop Aerial isĭescribed suitable for use on the LF and VLF bands together with aĬircuit of an interface loop tuner and preamplifier.
The article discusses the theory of loop aerials for receivingĪnd how they reduce the level of local noise. Reprinted in Communications Quarterly Spring Article originally Published in Amateur Radio August 1990 and
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