On Fri, 1 Jun 2012 13:16:33 -0700, "Sal M. O'Nella"
wrote:
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.
I beg to differ and hair split. The free space attenuation formula
works nicely at a distance of about 1 wavelength or more away from the
antenna. However, at the broadcast band wavelength of about 300
meters (about 1000ft), any attempt to steal power will probably
require near field calculations, or perhaps just transformer action.
http://en.wikipedia.org/wiki/Near_and_far_field
Next best bet: Get within 500 feet of a 50KW AM station, say KFI, AM-640 or
KBOI, AM-670.
RF safety exposure limits at 500ft for a 50KW AM station and 0dBi
antenna gain, yields about 1.5 mw/cm2. The safe limit is 100mw/cm2.
http://kb9mwr.dyndns.org/n9zia/rfsafety.main.cgi
Therefore, it is safe to approach the antenna without fear of having
your brain morph into Mr. Bialek. At about 60ft is becomes officially
unsafe.
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.
Technology to the rescue. Once upon a time in the 1960's, I lived in
Smog Angeles and worked part time next to an AM station. Surrounding
the antenna was the requisite chain link security fence, which had
several gaps in the fence for access gates. If one of the gates was
left open, forming a 1 turn coil, I could draw a small arc across the
gap with a clip lead. I wanted to fake an electrocution by bridging a
gate with both arms, but chickened out. When the station personnel
found out what us juvenile delinquents were doing, they promptly
buried a wire across each gate to short out the gaps, and changed the
locks on the gates.
Incidentally, locating the Gertsch/Singer (manufacturer of
communications service monitors) factory next to an AM broadcast
station (I forgot the call sign) in LA was not a great idea.
COMING NEXT ON THE POWER ROBBER CHANNEL: Tap into your neighbor's garden
lights -- it's easy!
Yech... The next revolution in home alternative energy will be the
nuclear powered underground water heater and the solar powered steam
plant. Dispose of hot nuclear waste and run your water heater at the
same time. If you do the math, solar steam power is cheaper and more
efficient than solar cells.
Somewhat more seriously, I've been reading about nantennas for solar
power. With 85% theoretical efficiency, it sure looks promising.
http://en.wikipedia.org/wiki/Nantenna
http://www.inl.gov/pdfs/nantenna.pdf
Maybe there's a place for RF engineers in alternative energy. All I
need to do is build a 3,000GHz antenna farm and find a diode that
works at that frequency.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558