Making Your Own Search Coils

themason
would pls give us a link to that schematic
thank you

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   I was hoping to find a group that discussed the actual making of a search coil for a metal detector to get some new ideas.  I don't see any here.
  I have build at least 20 TR metal detectors with coils and I was wondering what techniques others use.  The induction balance coils that I have build have a large coild shaped much like a horse shoe.  The receiver coil sits on the inner loop of the larger coil and is situated such that the receive signal is nulled out due to cancellation current within the setup. 
  The coil must resonate at the transmit frequency and so should the receiver if maximum sensitivity is to be had.
  Designing and build ing a coil for a "store bought" machine is a matter of matching the coil up to the impedances of the system.  If the metal detector is operating at 10 Khz, then the inductance must be adjusted so that resonance is achieved, regardless of the size of the coil.  As the series resistance of the wire goes up (the smaller the gauge), the tuning becomes less critical because the "Q" of the circuit decreases.  The "Q" or quality factor of a resonant circuit dictates how broad (in frequency) the tuning is.  However, the efficiency of the tuned circuit goes down.  So, there is a happy medium as to wire size and the practical aspect of building a coil. 
  At the least, you might need a multimeter or an oscilloscope to properly construct a coil.  This doesn't include any fixturing to support the finished coil.  I once build a coil on a wooden platform and used white glue to hold it in place.  The glue detuned the circuit.  Any comments.    Old_tex

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 Old_tex
Pual ignored i don't know why
any way i thank you for being so nice and answering me
i'll check the schematics you mentioned
thank you old_tex 
osama 

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Old_tex;

White glue, hmmmmm. ANY glue will increase the distributed capacitance! To a long time Ham and radio nut, in general, that is an oldy.... never make your coil and then coat it with coil dope!  (unless you have calculated in the increased capacitance.) 

On the topic of Litz wire, my research found there is more proximity loss, than anything else, to worry about. The old "honey-comb" radio coils had far less distributed capacitance, it is too bad there is not a way to do that for detector coils.

How is that for comment? 

goldigger

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		Quote:			Posted by Old_tex
	WA5MQR since 1962.   Electronics Engineer for 40 years. Old_tex

VE7EQP since 1986, electronics since 1952.... taught myself from my uncle's Can. Army manual. More formal stuff after that, though..... I originally wanted to be a geologist. Never got around to Ham until late!

Always was interested in gold and mining, tho.

goldigger

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