Don't waste your money on this article.  It is done using a coil 
salvaged from a transformer fed to an amplifier with lots of gain.  
Strictly AC, no DC response possible.   I consider the definition of 
"magnetometer"  requires DC response. Misleading advertising. As 
additional criticism, using a small coil salvaged from a transformer has 
very little window area (limiting the "effective antenna height" acting 
as another limit) if you intend to receive ELF.   Bah, humbug, $2 wasted.
Charles Patton
>> Hi, The "May 2007" issue of "elektor electronics"
>> magazine, contains an article using a loudspeaker
>> as a vibration sensor (seismograph). Plus an article
>> on ELF reception and a magnetometer.
>>
>> www.elektor-electronics.co.uk
>>
>>
>> May be of interest ?
>>
>>
>> Cheers Arie
>>
>>
>>
>>
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