Surf PI follow-up super results.....

[plumabob]

I've been experimenting with some different coil sizes and specs. Using 22AWG teflon coated stranded wire and using BB Sailors fast mono coil build as a guide, I hit upon what may be the optimum design. Here are the specs, coil measures 9.5 inches, .291mH, .83R. Construction is as follows. Started by forming coil, sewing with dental floss and using electrical tape to hold everything together. Then used 1/8th spiral wrap, followed by more tape. Then wrapped with a very flexible cloth tape ( 3M micropore ) and followed by more electrical tape to thicken it up a bit further. Shielded with scotch 1190 followed with a final wrap of electrical tape.

Not sure of the sampling speed but it does sample at the lowest possible delay adjustment on the Surf PI board. In other words I can not turn the pot any lower. I was very surprised with the following results as my other similar sizes coils I tried would come no way near them. This coil will see some very small pieces of gold jewelry and can hit a nickel at 15 inches. I know some skeptics will not believe this but build a similar coil yourself before you knock my results.

Right now I'm potting it up and will go for a field test of sorts soon. For a cable I'm using an Minelab Explorer factory cable. Cable is a dual coax design and very flexible.
Well there you have it. I hope someone else can build a similar one so that results can be shared and compared.

Thanks again Silverdog

[Vortxrex]

Wire Questions

Hi Plumabob, what type of teflon stranded wire are you using? Is it bare copper, or coated w/ tin or silver? Is there a brand name or part number for the wire?

Dave Frank

[nickel_n]

could you also tell us how many turns of wire is the coil made of?

[dfbowers]

I've been experimenting with some different coil sizes and specs. Using 22AWG teflon coated stranded wire and using BB Sailors fast mono coil build as a guide, I hit upon what may be the optimum design. Here are the specs, coil measures 9.5 inches, .291mH, .83R. Construction is as follows. Started by forming coil, sewing with dental floss and using electrical tape to hold everything together. Then used 1/8th spiral wrap, followed by more tape. Then wrapped with a very flexible cloth tape ( 3M micropore ) and followed by more electrical tape to thicken it up a bit further. Shielded with scotch 1190 followed with a final wrap of electrical tape.

Not sure of the sampling speed but it does sample at the lowest possible delay adjustment on the Surf PI board. In other words I can not turn the pot any lower. I was very surprised with the following results as my other similar sizes coils I tried would come no way near them. This coil will see some very small pieces of gold jewelry and can hit a nickel at 15 inches. I know some skeptics will not believe this but build a similar coil yourself before you knock my results.

Right now I'm potting it up and will go for a field test of sorts soon. For a cable I'm using an Minelab Explorer factory cable. Cable is a dual coax design and very flexible.
Well there you have it. I hope someone else can build a similar one so that results can be shared and compared.

Thanks again Silverdog

Bob,

That sound really impressive. My build only hits 7 or 8" for a nickel but I have my sampling set at 20us. I'm wondering if the early sample is the key to getting that distance, all things (besides the coil) being equal.

Since I have purpose built mine for water I'm not sure if there is any advantage to an early sample from a fast coil. Some have said like yourself ( I think) that you cannot sample any lower than about 20us in salt water?

I would be interested in knowing what your sample rate is actually set to as well as any component differences you have come up with as compared to Silverdogs parts kit.

Also, I would like to know from anyone else what distance you get with a 20us delay for a nickel.

Anyway, I was playing around with mine in the yard last weekend. I can get 2 - 3" deeper in my test garden over the Nautilus DMCIIb. The ground is really where we compare oranges to oranges anyway (or PIs to PIs)!!

Don

[jon-ecm]

Awesome!

Awesome sounding! I just ordered some awg 22 19 strand silver coated coper, hope it works! :P

I believe it can hit a nickel at 15 inches, My ATtiny 25 metal detector cleanly hits a nickel at 12" with a 8" coil made out of scraped microwave transformer wire no shielding or anything!
What I'm impressed with is the gold detection! My thing dosn't do very good with gold.
I'm making one like yours!

Would love to know exact wire and turns etc...

Thanks!
Jon

[bernte_one]

hello plumabob,

it would be helpful if i would post or link some pictures of the coil and the parts you have used to build it. Some nice ideas are hard to explain and to imagine.

[plumabob]

Ok Hi everybody...lots of questions. I'll try to answer them all. I did not change any components. Board was built with only the parts from Silverdog. The awg 22 is tin or silver plated 19 strand copper. I've had this wire a long time. There are no manufacturers markings that I can find. As far as the turns, I am not certain, I would believe about 22 give or take. I do not count as I measure inductance as I'm winding. Pictures will not help as It's already potted, but there are not any uncommon items used. Just the wire, black electrical tape. 1/8 inch nylon wire wrap and the micropore with is just a 1/2 inch flexible paper tape.

One more thing I failed to mention, I'm using a very sensitive set of headphones. I tried a few different sets and when I hooked these up I nearly blew out my eardrums. Have the volume turned way down. I made these myself. I robbed the speakers out of a broken set and installed them in these. Can't say for sure what brand they were but could have been Timberwolfs??? was a long time ago.

As for the delay I can't say. It's as low as the delay pot can be turned. Maybe Silverdog could step in and give some idea. Also it was me that said lower delay ratings will not work well in salt water, but in wet sand they can be used. A lot has to do with the size of the coil the depth you are working and the wave action. There are conditions where settings of 10us -12us would work. I live on Long Island so that is what happens here. Areas like Florida may be different.

I'll be finishing her up in a couple of days and hope to get out for a field test. I have the board in a small waterproof Otterbox with waterproofed pots and switches. Upon completion i will post some pics.

[TH Jim]

Hi Guys,

Just as a comparison -> I made my coil out of 0.5mm thick enamell coated wire salvaged from a transformer, 24 turns at 8.6 inches, covered in aluminium kitchen foil shield, don't know what the inductance is as I cant measure it but it works with the delay adjusted to min on my surf pi. Will have to track down a nickle (is that 10 or 25 US cents?) and try it. Mine will get a British 10 pence at about 10 inches and a thin gold band at about 6 inches. Will try and post some pics.

Cheers, Jim.

[plumabob]

Have it pretty much finished, now. I'll get some pics up soon. One more thing I noticed. Mabye you guys could try this yourself. Even though I'm hitting a nickel at 15 inches, a quarter which is a better conductor only hits at 12 inches or so. I would have thought the reverse would have been true.

[dfbowers]

Hi Guys,

Just as a comparison -> I made my coil out of 0.5mm thick enamell coated wire salvaged from a transformer, 24 turns at 8.6 inches, covered in aluminium kitchen foil shield, don't know what the inductance is as I cant measure it but it works with the delay adjusted to min on my surf pi. Will have to track down a nickle (is that 10 or 25 US cents?) and try it. Mine will get a British 10 pence at about 10 inches and a thin gold band at about 6 inches. Will try and post some pics.

Cheers, Jim.

5 cents.. It's a lower conductor than 10 or 25 (which are copper clad) . It falls close a pull tab or some thinner gold bands, but higher than aluminum foil.

[plumabob]

Here are a couple of pics....

[TH Jim]

Hi folks,

Found myself a nickle and gave my surf pi a test - here are my results:

10 inches - faint but definately audible
8 inches - reasonable clearly audible
6 inches - screaming ear drum damage!

Does anyone else think it might be a good idea if members of the forum could agree on using a standardized set of test targets so we can compare results more easily???

I havent thought of what these test targets could be - they would need to be something easily available all over the world - any ideas?

I might start a new thread on this subject.

Cheers, Jim.

[plumabob]

Hi Jim,

Here in the states most would agree that a nickel is a close match to jewelry type gold. So for that reason it is a good coin for testing a PI. Nice results by the way!

Bob

[bernte_one]

or square cutted aluminium foil pieces

or go to a bank and change Euro coins into US$ Coins or otherwise

[dfbowers]

Hi folks,

Found myself a nickle and gave my surf pi a test - here are my results:

10 inches - faint but definately audible
8 inches - reasonable clearly audible
6 inches - screaming ear drum damage!

Does anyone else think it might be a good idea if members of the forum could agree on using a standardized set of test targets so we can compare results more easily???

I havent thought of what these test targets could be - they would need to be something easily available all over the world - any ideas?

I might start a new thread on this subject.

Cheers, Jim.

Jim,

What do you have your delay set to? I think to do any meaningful comparison, we all need to state where we have our delay set (if you have a scope that is..)

Don