Michel wrote: > Indeed a primary with an open secondary behaves > like a pure inductor, so it's a purely reactive > load, so current in it can be made to oscillate > non dissipatively (assuming resistance of the > coil is negligible). In terms of transformer it > makes perfect sense. But in terms of antenna, > how could the open air coil antenna help emitting > radio waves (which requires power) towards infinity?
That's just it, the coil isn't an antenna. Or it's not a very good one. Some electromagnetic radiation is bound to escape from such a coil, but it can be designed to minimize that effect. An LC circuit can oscillate without radiating very much unless it has an antenna configured in such a way as to resonate with the permittivity and permeablity of free space. Otherwise, radio and TV stations could have nice compact oscillators instead of those big antenna towers. Also, electric power transmission lines would be useless because they would be emitting EM radiation at 6OHz (50Hz in Europe) and hardly any power would reach its intended destination. This is a near field effect, not EM radiation. In other words, the receiver is less than a wavelength from the emitter. The emitter/oscillator would draw a minimum of power until a nearby resonant receiver could become a power draw itself. Please pardon this somewhat homemade explanation. I came very late in life to an interest in EM phenomena, and my knowledge of it is, shall we say, less than sophisticated. M. _______________________________________________ Join Excite! - http://www.excite.com The most personalized portal on the Web!
