Please tell us how your wonderful deep penetrating Surf PI 1.2 coil is made.

[kenny444]

I think a thank you to Eric Foster for those words of wisdom is due. Grateful.

[kt315]

this is dual field coil pics. Whites. this is the patent. http://www.google.com/patents/US7994789

[godigit1]

For your review!! And thank you Chet and all for convinceing me to finally try a basket coil out.




I just finished this basket coil for my Sm pro kit. I used 30 guage radio shack plastic coated wire.
I used the form provided on the Chance Pi coil thread . It is working the best of any of my coils so far. I am primarially looking for gold sensativity in my coils and use the earing in the pictures as my minimum acceptable target. (earing weighs .5 gram) Before this coil with regular fast coil design I could only get it at 3 inches with a 4 inch coil.

Super suprise when I got it all tuned to my Pi I can now hit the earing at about 4 inches with this 8 x10 basket coil.
I also changed out my 5534 for a max 410 and the differance was huge as far as waveform clarity. I will provide some scope pictures when I get it hooked back up. I removed it to put on my last wrap of teflon.

So here is my improvement to the basket design using small guage single strand wire and every 5 wraps I wrap two layers of teflon tape to increase spacing and dialectric and hopeing to reduce capacitance. Also the tape holds the windings in form on the coil form as the oval shape makes them want to pull out of form on the sharper corners.
I went 20 wraps but had to remove one I tried two but had to put one back 19 works well.

The rock in the pictures is a hematite chunk I use for a ground sample. the coil does pick it up slightly but with audio after you leave the target. And almost providing the boing sound that a vlf does on negitive cold rocks. I can place the sample in the center of the coil and it does not effect my depth. If I use it to shield the nugget I still get the nugget as positve response. This peice of hematite totally overloads my VLF detectors and the ground it came from was undetectable. I am no expert in coils and there may be inhearent problems with this coil I have not had it outside yet so that is still unknown. It does have slight sensativity to my hand so that may be a concearn and i may have to shield it.

Here are some of the depths and I have the sens and threshold almost completly silent, when I get outside Ill be able to crank it up and I cant wait to see
if the depth will be close in the ground.
1/2 gram earring 4 inches
1.2 gram nugget almost 7 inches
silver quarter 7 inches
silver dime 8 plus
nickel 10 plus
2 gram gold ring
10 plus
and these are good responses I can hear with my headphones not on my head but around my neck.
Also as Kt 315 has stated I think this design would lend itself for a dual wrap. notch the tabs in the center and wrap a tx or rx coil over the center coil Im not sure which would be on the inside.
you can bet Ill be playing with that...
Hope this can be of use!!

http://www.geotech1.com/forums/showt...-the-MPP/page1 KRinAZ has some improved Basket weave templates in the last pages.

[kt315]

nice done Godigit. do NOT fill it by epoxy - ! put in a housing, cover by something, scotch tape, and then after fill by epoxy above. ie all winding has to be IN AIR, NOT in epoxy. an epoxy ll increase the transfer capacitance of the winding that ll bad.

[godigit1]

Bummer something happend and I lost some sensativity.
I was cranking up the coil current to see how far I could push it and at 100mv I blew out my damping set up (AGAIN)
I replaced my pot and the unit is deminished. No matter how I tune I cant get those inches back. my sensativity pot has to be cranked up higher just to operate and before I had to turn it all the way down. I lost almost 2 inches on my small targets.
The only changes were cutting of the extra wrap I still had attached while tuning and a final wrap of teflon.
Maybe the slightly less resistance is causing the coil to have lost some voltage? (My debugging skills suck)that being said Im still getting better performance on small items for the size of the coil then I have from my other coils.
The 410 amp gets better depth across the board but has a strange waveform.
Their is a huge differance where these two amps tune to 0v at pin six(complete other end of the pot) So both Pin 6 has to be calibrated and the damping has to be redone between amps.
Here are the scope shots of the 410 vs the 5534. I am very much a rookie but it looks like this coil is hitting at 5us. The scope is set at 2 us and 2 volts.

The 410 is the first shot.
I don't want to go to off topic on this thread so I will stop there but I wanted to provide a update on the coil for you.
Best

[kenny444]

Hello I hope you all got something nice over the holiday, I got 70 feet of Teflon coated wire from a nice man in the USA, to go into my 14" coil housing (when it arrives) the wire is 24 AWG, 19 strand, working with the coil calculator I appear to need 17 turns to get 340uH, I can also wind 16.5 turns for 321uH or 16 for 302uh. Can someone please tell me what is considered the best inductance for the Surf PI 1.2 Thank you.

[kenny444]

Hello Silver Dollar, I now have 70 ft (21Mt) of 24 awg Teflon coated 19 strand cable, I also have the 14" coil housing, I will need to get a forming base and plan out the winding support positions. Then I can wind the coil, can you tell me please if you are aware of the optimum inductance. This length and the housing will allow me just over 20 turns. The 24 awg size to .51 but the coating brings this up to 1.07mm, using the coil calculator at .51 with 16 turns gives me 300uH where as 1.07 with 17 turns gives me 309uH. Advice would be appreciated. Thank you.

[Silver Dollar]

Well the generally accepted standard value is 300uh so your 16 or 17 turns should be just about perfect.

I don't have a Surf PI so do not know if it needs a different value. The optimum would be based on the
pulse rate and pulse width as well as the size target you are after. Most any value can work but you would
need to use a scope and set the damping resistor for any given value...

[kenny444]

Thank you, 300uH is the target, I will hunt for test point pictures and see what can be seen. Grateful

[godigit1]

http://www.geotech1.com/forums/showt...uda-and-SurfPI

[kenny444]

That is a most useful post, thank you for posting "godigit1" and thank you for writing "Tepco" I am now left with the following to do; getting a coil building board big enough for the new 14" coil housing; waiting for the postal system to deliver my cup hooks, getting a pot to fiddle with, get the oscilloscope to work, (I even bought a laptop usb scope, but the chinese instructions have so far failed me) still waiting for alternative 4093 to try out. I think there may be light at the end of the tunnel, grateful for all that has been written and added to this thread.

[kenny444]

Well here is my "no progress report" The surf PI 1.2 boards (I have 2 are set to as near to zero as the meter will allow) seem to be OK apart from constant chirping that I cannot get rid off "any Help appreciated"
I made a coil former for the 14 inch housing and wound a coil using 24awg, 19 strand Teflon covered cable, 320uH 1R8, I tied the loops with braided nylon (fly reel backing) to keep the coil tidy and half covered it in spiral wrap (stopped because of sore fingers), dropped the coil into the housing, having left plenty of cable to go direct to the control box tested it (Chirp chirp chirp) very little response. So I then took the detector outside and waved it around, it is going off all by itself even in free air when it is moved??????????? so back in it came and it is as deaf as a post. So I made another coil with 30awg, 7 strand, 250uH but 4R7, also deaf. So can some please tell me what the TUNE knob is supposed to do as it seems to nothing, the delay pot seems to do nothing, so I am thinking damping resistor. I am basically at a point where I do not know what to do next. Any clues please.

[godigit1]

You have to damp each coil individually. Also play with coil voltage as to much also causes my coils to go dead. Some are more forgiving than others. My basket coils have a very close window of operation. I have the smpro kit from ebay so we are not comparing apples with apples but the post above is for the 1.2.
Basically 0 pin six of the 5534, After attach your scope and look at the signal you will see what is going on. The pics above are good examples. By playing with a damping resistor set up and the coil voltage you can dial it in. You should be both watching the scope and testing for performance on the types of targets you prefer to hunt. The combination may be a bit tricky at first but you will quickly see the results of what your doing. Make sure it operates through the full range of your delay pot if the 1.2 has that. Double check pin 6 of the 5534 voltage and adjust if needed and do final adjustment of the damping resistor.
Your almost there good luck!!!

P.S You may want to set your damping resistor up with pins for easy removel and testing or replacement. I use the gold plated D sub connector pins. reinforce the female side with shrink wrap and they fit real snug. I get them from the shack but Im sure there are less costly options.

[kenny444]

Thank you I have put about 8 hours in today looking and hopefully learning, I can see both offset and delay, but what I do not know is "what is right and what is wrong" I assume the Tepco surf3jpg is correct and I have very similar, when I adjust the offset both sides of zero I see the difference, but I see little change in the delay wave form. I am trying first with a good coil (well 6 inches for a gold ring and a pound coin. then I shall try the new big coil with a different pcb and see what I can. Thanks again.

[godigit1]

Ahh I think thats where you are missing it. You have to set the offset to 0 and leave it! Then adjust the damping resistor for no ringing.
What resistor does the 1.2 kit come with? My kit came with a 680hm and my best basket coil damps at 348 ohm. As far as coil voltage on my unit I measure it from + to - of my coil connetor and R2 is the pot to adjust. Try 35 t0 40 mv.
You really need to have a adjustable resistor set up (IT IS PARAMOUNT). http://www.geotech1.com/forums/showt...mping+resistor
Post # 4.

Also you might trying taking off a loop of wire, but keep it connected in case things get worse then try adding one. I have been adding extra loops then removing to best performance for my targets.

Surf3jpeg is somewhat the ideal but the 4jpg is more where I get better performance to small items with my round coils.
Thats why I also use target specimens.
Hope this helps it can be frustrating.