Is it necessary to make a shield in the Baracuda's coil?

[Fabian]

Hello everyone. I'm about to take my vacation at the beach and built my second Baracuda to "play" a bit and as I have little time, I hurried and shut the coil without putting the shield. My question is: Is it necessary? I read somewhere that a PI coil can work well on the beach without shielding. Is it so? How could try it if I have a beach nearby? or How I can reproduce the conditions of wet sand? I do not want to get there (2000 km) and discover that it does not work.

Any suggestions or information would be welcome.

Thanks in advance,

Fabian

[kt315]

good book for everybody is INSIDE THE METAL DETECTOR, of authors George and Carl Moreland. By The Way, Carl is the administrator of the forum GEOTECH,
so I suggest for first to take knowledge from this great book, to stand up a level in electronics reading the useful book, nice book for reading in craft lifting to vacation place
and in vacation time.

good luck!

[Fabian]

Thanks for the advice, kt315, but unfortunately it is not possible for me to buy the book written by George and Carl because the shipping costs are very high for South America. Even the dollar value of the book makes it unattainable for me.

But hey, if it's so difficult to answer this simple question, I will find the solution on my own.


Fabian

[Qiaozhi]

Hello everyone. I'm about to take my vacation at the beach and built my second Baracuda to "play" a bit and as I have little time, I hurried and shut the coil without putting the shield. My question is: Is it necessary? I read somewhere that a PI coil can work well on the beach without shielding. Is it so? How could try it if I have a beach nearby? or How I can reproduce the conditions of wet sand? I do not want to get there (2000 km) and discover that it does not work.

Any suggestions or information would be welcome.

Thanks in advance,

Fabian

The purpose of the shield (often called a Faraday shield) is to reduce the capacitance between the coil and the ground. It also eliminates false signals due to static buildup on the coil, and reduces the effects of external electromagnetic interference.
PI detectors that use coil frames (e.g. 1m x 1m) do not need to be shielded, as these use a long main sample delay.
So, in answer to your question, it would be advisable to shield the Baracuda coil.

[Silver Dollar]

You could do a test by adding salt and water to some sand in a bucket.

I thought PI's did well on dry sand and in the water but not in wet sand.

Shielding isn't needed at longer delays so if you get there and have problems just adjust
your delay and keep looking. You might miss gold chains but should still find stuff.

I haven't got one working yet to try myself...

[Fabian]

Thanks Qiaozhi. I was reluctant to disarm my coil had been so nice, but I see no other solution than done.

Thank you too, Silver Dollar.

Fabian

[Qiaozhi]

I thought PI's did well on dry sand and in the water but not in wet sand.

If the PI is set with a short delay (less than 15us) it can produce a false response in sand that is wet with salty water.
The chemical name for salt is sodium chloride. When wet, this forms an electrolyte which can conduct electricity.

[Fabian]

Thanks again, Qiaozhi. I already made the shield to the coil. I have got another (the last one) question about this point:I made it with mylar that I took from an old capacitor. I have a resistance of 650 omhs from one end to the other of the shield: Is that value for the shield right? It is the first time that I use mylar. For my other coils I used aluminum foil and it worked fine.

From already I thank for their response.

Fabián

[Fabian]

To close the thread, commented that finally I returned to the aluminum foil, for lack of time.
Next time I will try with the mylar, because it is very convenient to put it around the coil.

regards,

Fabian

[kt315]

PLEASE DO NOT USE ALUMINUM FOIL IN PI COIL DESIGN! I ASK YOU - DO NOT USE THE FOIL IN PULSE INDUCTION COILS!

[sinclairuser]

the mylar was fine, kt315 is right ally foil is seen as a target by pi's.
been there done that.

[Fabian]

My other Baracuda has aluminum shield and has no problem. Already tried it several times on the beach and it works perfect on wet and dry sand. With it I found many targets of silver and a lot of coins (And soooo many nails and pulltabs ) at good depth.

Anyway, the coil is now closed and I'll see on the beach as it performs.

To kt315: Was not simpler answer my first question, instead of telling me what to use or not NOW? Much appreciate your intention, but I do not understand your behavior ... Thanks anyway.

Regards,

Fabian

[Qiaozhi]

My other Baracuda has aluminum shield and has no problem. Already tried it several times on the beach and it works perfect on wet and dry sand. With it I found many targets of silver and a lot of coins (And soooo many nails and pulltabs ) at good depth.

I have also used sticky backed aluminium tape (20um thick) for shielding a PI coil, and it worked just fine. Eric Foster uses lead tape in his PI coils, but this is now quite difficult to find. Although I've heard you can buy it from a golf store, where it's used to balance golf clubs.

I'd be interested to know if you notice any difference between a mylar shield and an aluminium one.

P.S. I've just seen lead tape on the UK eBay website: 1"x100" for £4.99 + £2.99 delivery.

[kt315]

Fabian, you need in PROTECTION FROM ELECTROSTATIC FIELDS, NOT FROM ELECTROMAGNETIC FIELDS! DO you UNDERSTAND ME NOW???

[Fabian]

I have also used sticky backed aluminium tape (20um thick) for shielding a PI coil, and it worked just fine. Eric Foster uses lead tape in his PI coils, but this is now quite difficult to find. Although I've heard you can buy it from a golf store, where it's used to balance golf clubs.

I'd be interested to know if you notice any difference between a mylar shield and an aluminium one.

P.S. I've just seen lead tape on the UK eBay website: 1"x100" for £4.99 + £2.99 delivery.

Hello Qiaozhi. Unfortunately, I do not think I have time to wind a new coil before leaving, but I'll do my best to make it. If it could be used, would be a great thing, because the mylar is already cut into strips and is very convenient to use.

Greetings.

Fabian