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designing an antenna to transmit a VLF signal over 10 meter

 
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sliders_alpha
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Joined: 19 Jan 2009
Posts: 8

PostPosted: Tue Mar 16, 2010 3:42 am    Post subject: designing an antenna to transmit a VLF signal over 10 meter Reply with quote

hi,

so, i've retrieved a signal from a remote, i've use a coil of copper wired, around 30 turn around my hand, and capture it with a PC sound card



spectrum of signal N2



i'm only familiar with AM modulation, according to the spectrum, this is not.
also, untill now, i only used AUREL 433MHz module, i've never designed a radio transmitter before

how would you design an antenna capable of sending this?

thanks =D
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sliders_alpha
Semi Newbie


Joined: 19 Jan 2009
Posts: 8

PostPosted: Wed Mar 17, 2010 8:06 am    Post subject: Reply with quote

well, don't bother^^

this signal is shit, i've talk with some people and my spectrum shouldn't look like this

it's because the "resonance" frequency of my coil was too high so i didn't retrieve a good signal

it was made with 10 meter of wire turned around my hand, according to those people i should use at least 140m

and if you want to know, this signal is used in supermarket to lock shopping cart, each cart's wheel has it's own embedded system, and when this signal is received, it trigger a mechanical part wich lock the
wheel

my next move is to dress like a ninja, wait till it's night, and retrieve a wheel in order to get a proper antenna
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Alan
Site Admin


Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Sun Mar 21, 2010 6:11 am    Post subject: Reply with quote

That should be a funny hack, there is an Instructable about how to make one. Let us know how you make out.

http://www.instructables.com/id/EMP-shopping-cart-locker/
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sliders_alpha
Semi Newbie


Joined: 19 Jan 2009
Posts: 8

PostPosted: Thu Mar 25, 2010 9:31 am    Post subject: Reply with quote

AWE-SOME =D

i didn't tought about filtering it, know i kinda ha something (it doesn't look like their signal tho, but i'm in france, and i think we are using GS1)



now we have something, allright, i'm going to built an emmiter based on their

i was kinda stuck because i couldn't find any supermarket with a similar system around (in order to steal a couple of wheels to get an antenna and do some test)
thanks

#EDIT

WAIT, this is awesome

i've got exactly the same signal BUT my carier is at 4.8KHz



what do you think? for security reason, the carrier frequency can be chosen in a certain window?
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