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Hopefully not off topic
"Sal M. O'Nella" wrote in message
... I share your skepticism, Ian, and I'd like to take it a step further. There is real math (imagine that!) to address the notion of "stealing power from a nearby transmitter." Free-space attenuation is given by the formula 20 log Rf + 37dB, where R is the range in Nautical Miles and f is the frequency in MHz. True, a close-in VLF transmitter gives good coupling and actually will light an unconnected fluorescent tube. However, these stations are quite rare and nobody moves near them to "steal power," since they are built in large open areas with fences and guards. Need backup plan. Next best bet: Get within 500 feet of a 50KW AM station, say KFI, AM-640 or KBOI, AM-670. Per the formula, the coupling loss will be about 13 dB, making 2500 watts of power available to you at that location. However, to realize that power, you need an antenna with near unity gain at that frequency. Any guesses as to how much they cost? Try $Millions. (It's called a 600-foot tower.) Much better to call your local utility and tell them how much you appreciate their service. Resolve to be more realistic about power-robbing schemes. COMING NEXT ON THE POWER ROBBER CHANNEL: Tap into your neighbor's garden lights -- it's easy! 73, "Sal" Hello Sal. Thank you very much for the maths and the workings. Stories of "getting useable power from a transmitter" are always hard to track to an accurate source. The nearst I've gotten is a friend who knew of a cottage with a 33kV power line passing overhead. Seems that some turns of wire were fitted under the cottage's eaves and some useful power was obtained. Transfoemer action, I assume. I've read science fiction stories form the 1930s where "broadcast power" was in general use. One story had all users switch off their powere receivers so that the authorities could D/F a wanted person by measuring the strength of the power field. Ah - unfettered imagination though induction does work when the power source and appliance are close together. 73, Ian. |
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