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"Ceriel Nosforit" wrote in message
news ![]() Hehe. Well yeah, I figured as much, but why doesn't it work? Too high impendance? Why is that something the amp can't handle, if I maybe resist the urge to crank it up to eleven? No. The problem is that wavelength of a, say, 10kHz signal is 3km in free space. You need to have an antenna that's a decent fraction of that length for the antenna to look "distributed" enough (that is, the phase of your 10kHz signal at the far end of the wire is significantly different than that at the near end) in your to start getting any radiation. You can go through the math for all this -- look up the input impedance of a short dipole on Google -- and you'll find that the radiation resistance of a reasonable length speaker wire is probably going to be in the milliohms, yet the finite (real) resistance of the wire is going to be 10-1000 times as much, and the reactance will be as well. Hence, all three parameters are against you: The high reactance will keep the amps from being able to put much power into the cable in the first place, and of what does get there, the vast majority will be eaten up as heat rather than radiating. To make matching tenable (so that you can actually get power into the cable), you need a *very* long wire. To make things efficient, you need low loss conductors -- nice, thick metal rods. Hence, doing a good job becomes rather spendy, and thus you don't see that many people outside of the military building VLF systems. I think I'd almost suggest trying something like a 1.3GHz moonbounce system prior to building your own VLF transmitter... |