my DIY Surf PI 1.2 coil problem

[gdogg]

My DIY coil problem is , dam thing is detecting iron, with very strong signal. gold very low and barley even signal.

what i have done, is i have wound up 0.5 copper 25 cm wide and 21 turns. I have also wrapped it in aluminum foil, as it has strengthen the signal, and insulated in electrical tape.

i am getting great signals on iron, tools, spanners etc from nearly a meter distance, and has low conductance on my gold ring, cant barly hear it, almost so close that it is touching.

what have i done wrong.

cheers

[Davor]

How about a photo of it?
When answering, go to advanced, and you'll find attachment options there.

[Qiaozhi]

My DIY coil problem is , dam thing is detecting iron, with very strong signal. gold very low and barley even signal.

what i have done, is i have wound up 0.5 copper 25 cm wide and 21 turns. I have also wrapped it in aluminum foil, as it has strengthen the signal, and insulated in electrical tape.

i am getting great signals on iron, tools, spanners etc from nearly a meter distance, and has low conductance on my gold ring, cant barly hear it, almost so close that it is touching.

what have i done wrong.

cheers

Probably there's nothing wrong with the detector, as PIs love iron.
The weak detection on a gold ring may be due to your sample delay being set too high.
You'll have to provide more details of the setup of your detector before anyone can comment further.

[sdesic]

I had same results with my surf pi pro
I used iron to set maximum depth on detection - used 50k trimmer for delay and it was all the way.
Got more depth but lost gold ring - no detection ...
Gold coin was still there - detected on about 15 cm

[porkluvr]

Of course you know that any shield material should be somewhat distant from the coil windings. Using two layers of low DC spiral wrap* might be a worthwhile addition between the coil and the shield. It comes in different id and od sizes.

*PTFE (such as Teflon) material has lowest Dielectric Constant for this purpose but is right expensive. Polyetheylene is a good second choice. If you can, check the specs, as there are different grades of PE.

[gdogg]

thanx guys for the response, hey what i really want is a Pulse Induction, Multi Period Fast (MPF) Gold Detector schematic, more designed for seeking gold, and i know i might be asking the impossible, but im curious with he MPF stuff.

[porkluvr]

I guess that means that we won't get to see any pictures. Go ahead and change the subject.

[Thomas]

porkluvr, what about this stuff?, It's really inexpensive here, 6 rolls for a dollar at the dollarstore.

[porkluvr]

porkluvr, what about this stuff?[ATTACH]30987[/ATTACH], It's really inexpensive here, 6 rolls for a dollar at the dollarstore.

Good ol' thread sealing tape is made of PTFE and is dandy but I am afraid it is way too thin unless you are willing to wrap many, many layers.

I have not made any measurements but I'm thinking that 0.125" separation might be acceptable, but then 0.25" separation would be much better so far as minimizing capacitance between the coil and shield and reducing flyback decay time. What works depends on how low you are trying to go.

[Thomas]

Ya, I was thinking the same, but at such a low price I could use a lot. Polyethylene would be quicker and it's not bad for the price, can you see that I'm a price sensitive nut?. Hahaha

[gdogg]

here is a pic of my DIY coils one 25cm and the other 10cm wide






i also am playing around with 2 coils, outer ring and inner, one large and small, both are wired together.
https://www.youtube.com/watch?v=ejLnN3aB5vg

[porkluvr]

If you intend to hunt for gold or other short tc targets you should not make coils with enameled wire because excess inter-winding capacitance might not allow your transmitter flyback to end quickly enough for those targets to be detected.



edit: Eric Foster is repute to have used PVC insulated TIN plated stranded wire in his coils. Stranded Teflon insulated TIN plated wire would probably be superior except for the fact that there is practically no such thing because of manufacturing costs tradeoffs, making silver plating a less expensive alternative in the manufacture of stranded Teflon insulated wire, rather than tin plating.

There is practically no market for "stranded tin plated PTFE insulated wire" because a silver plating process is MUCH less expensive to implement.

Believe me or no, consider this: US military is probably the largest consumer and they don't take second best. So long as they aren't in the business of producing "fast PI coils" they would have little use for tin plated wire on their high dollar fighter jets and etc..

There is no military surplus aftermarket for TIN plated stranded Teflon insulated wire because the product (practically) does not exist.

If you think you've found the stuff, you've probably been misinformed by the seller or else you will pay dearly for the product.

[gdogg]

thanx for the info, as i am a newbie at this.

[baum7154]

thanx guys for the response, hey what i really want is a Pulse Induction, Multi Period Fast (MPF) Gold Detector schematic, more designed for seeking gold, and i know i might be asking the impossible, but im curious with he MPF stuff.

-------

It sounds to me like you want a CHANCE PI from Silverdog if he will once again offer the boards/lots. The CHANCE PI BUILD and the CHANCE PI COIL threads detail a lot of info on this detector and it has MPS.

regards,

Dan

[Silver Dollar]

Shh don't tell anyone, this place has 26 gauge PTFE tinned wire...
http://www.surplussales.com/Wire-Cable/Wire4.html