Beginner would like to build Sandbanks PI Metal Detector

You guys are fantastic, Cornelius, I told my wife you were sending me a completed PI unit and she said " see there are still nice people in the world !" Dude I can't thank you enough, except to say if you ever need any automotive advice ask away.
 Man I can't wait to get it, I'm gonna start working on the coil right away. One question, can  different size coils be made for interchangeabilty  for size and depth of objects being searched for ?
  Again  thanks alot Cornelius
 
   Aliman

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Hey guys, I was reading the Sandbanks PI instructions and at the bottom of page 7 under "Response Speed" it talks about optimising the detector, "To get the very best from your ?Sandbanks? several things
can be optimised, but the first step is to fit a printed circuit coil,
as described in the April 1979 issue" .
Where would you install this " Printed ciruit coil, it talks about?

Aliman

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Thanks for clearing that up Carlos, thats kinda what I thought.
OK , I've completed the coil, now should the wire running from the coil to the detector be of a shielded type, two or three conductor.
Also I've seen the "Hammerhead PI" and that article shows them applying a Faraday shield of aluminum tape around the coil, should I do the same for my coil, or is that strictly for his design.
One more question, can anybody show me a diagram of the actual connection between the coil and the cable extension , do the pigtails coming from the coil connect to One conductor or two separate conductors ?

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		Quote:			Posted by GoldDigger1950
	Aliman, never put a Faraday shield completely around a radiating coil. That would literally prevent the coil from radiating. Instead, use an old Frisbee toy and line the inside of it. Glue your coil inside on top of the foil and you will keep it from sensing things from the sides and above. I actually only recommend a Faraday shield on a very large coil that might accidentally detect a vehicle which is towing it or something like that.

Yep! the Original pans did not call for the shield.

Get it up and running and then play.

The plans only called for zip wire unshielded but you can use coaxial if you wish.

I used 18 SWG shielded wire.

Later you can do the shield and run it to ground.

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		Quote:			Posted by Cornelius
	Al , do as Homefire tells you . Keep the coil as it is described in the literature . Lateron you can experement with it . One way to do that is winding aluminum foil aroud the windings , but with a gap at the end  ( so the aluminum is not going around the whole coil  )  . Using a wire to ty the aluminum  foil tight around the coil wouls do the job .  Connect the foil and the tying wire to ground . But only do this when you have the detector going and you want to play with it some more . I never did !!!!!!  Cornelius

Cornelius, I wouldn't advise wrapping metal foil around a radiating coil. If the coil was an oscillator coil only,that is all right but as a TX coil, the metal foil will diminish the radiating signal by at least half and the wire you suggest for holding it will appear as a huge target and swamp the receiver. The purpose of a Faraday shield is to keep the radiating field to a minimum and that would defeat the TX coil entirely.

As I suggested, a half shield above and along the sides on a large coil can be a benefit but wrapping the entire coil is a no-no.

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