Chance PI coil...

[slowsweeper]

yep i get it now,thanks,that translation diagram threw me with the green and blue representing the wire,i read it as two seperate wires.

[baum7154]

hello geocash1,you seem to be the right person to ask about this basket coil and the winding of it, could tell me what you do with the ends of the two wires once youve completed the 5 loops for each wire ,do you join them or leave them open,obviously the other ends of the two wires go to the mpp board ,hope you or any one could help,thanks.

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to clarify: the significance of the 5 turns is that is the point that you must jog one slot to avoid laying your wire parallel to the previous wire in the slot. A 30 turn coil will require 6 jogs in order to avoid parallel wires in the slots and to have your start and finish wires close to each other. A 29 turn coil only needs 5 jogs I believe.

Dan

[kellogs]

Reply from kellogs

Hi mate i see that you have been put on the right track like you i am only new to this hobby and the help you receive from the members is great as i don't have an oscilloscope as yet both baum 7154 and chet have helped me heaps if you look back to a post to kellogs post 68 from chet his advice worked great for me and also baum7154 post 563 wish nyou all the best keep in touch i hope to do some field test this week Regards kellogs

[baum7154]

I have built a 4" X 12.5" oval coil with 8.5" parallel sides in accordance with Eric's 3:1 profile recommendation. This coil is a fast spider coil using the instructions I posted in post #126 using only simple tools. The construction pictures are posted below. I will post test results for this self shielding coil in the next few days.[ATTACH]31039[/ATTACH][ATTACH]31035[/ATTACH][ATTACH]31036[/ATTACH][ATTACH]31038[/ATTACH]

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Well it's been much more than a few days since I posted the above info. About 4 months have passed since the above post and I finally got the time to complete testing on this new coil today. Nothing worth while is ever easy and this is no exception. I had to remove the 430 kHz filters from the CHANCE PI and installed the 530 filters but still did not like the results on small gold so then installed the original 680 kHz filters. Also the adjustable damping network had to be reworked to properly damp the coils. The new damping network adjusts from 1075 to 1245 ohms.

The object of these tests was to compare my 335 uh round coil to the new 4" X 12.5" 328 uh parallel side 3:1 oval coil on small gold targets. These 'small gold targets' are the most difficult I have and are as follows:

1. Gold flakes in glass vial - largest piece is .95 grain, 2 pieces - .19 grain, 1 piece - .12 grain, 1 piece - .11 grain. Total weight of all dust and flakes 2.92 grains. With the flakes loose in a glass vial it is hard to present the target consistently to the coil as the pieces can shift or be on edge.

2. 4.5 grain, 14 kt jewelry gold head for mounting a 4mm stone. No earring post or other metal.

3. 1/4" X 1/4" .004" thick piece of aluminum soda can.

All tests were conducted at a Guard Interval of 10 (8us) on the CHANCE PI detector. Battery voltage throughout the tests was 12.6 volts. Only repeatable test results are accepted in these tests. In many cases greater 1st Detection Distances were observed but not consistently repeatable and so were not included in the results. Test coil was placed horizontal 20" above table and test was conducted in air. Table was slate with no other metal in the area of the coil.

1st Detection Distance Tests:

Target ---------------------------8" Round Coil Distance ---------------------Oval Coil Distance

Gold Flakes ---------------------1.75" -----------------------------------------1"

4.5 gr Head ---------------------4.75" -----------------------------------------3.5"

1/4" X 1/4" AL ------------------4.5" ------------------------------------------2.75"



Solid Detection Tone Distance:

Target -------------------------------8" Round Coil Distance --------------------Oval Coil Distance

Gold Flakes -------------------------0.5" -----------------------------------------.375"

4.5 gr Head -------------------------2.75" ----------------------------------------1.75"

1/4" X 1/4" AL ----------------------2.75" ----------------------------------------1.75"

Conclusion: It is clear that the 8" round coil has a depth advantage but its field is a virtual pinpoint at the greatest distances recorded, making it difficult to quickly cover an area in the field. While the Oval coil has a bit less depth it has an 8" blade like field that will cover an area much more quickly. It will be interesting to see how these coils perform over soil once the snow clears here.

Regards,

Dan

[Chet]

Hi Dan

Still impressive results. Many Pulse Induction detectors will not even see the gold flakes. I agree with the coverage of the Bigfoot style coil and plan on winding one later.

Thank you for the update,
Chet

[green]

[Conclusion: It is clear that the 8" round coil has a depth advantage but its field is a virtual pinpoint at the greatest distances recorded, making it difficult to quickly cover an area in the field. While the Oval coil has a bit less depth it has an 8" blade like field that will cover an area much more quickly. It will be interesting to see how these coils perform over soil once the snow clears here.]

Hi Dan, interesting test. The round tested better for me too, but I still like the rectangle shape. For me the round coil target signal strength was very close out to half the radius off center. I'm wondering how far off center you get before the target detection distance drops below the rectangle detection distance. If you do some more testing.

Thanks green

[baum7154]

[Conclusion: It is clear that the 8" round coil has a depth advantage but its field is a virtual pinpoint at the greatest distances recorded, making it difficult to quickly cover an area in the field. While the Oval coil has a bit less depth it has an 8" blade like field that will cover an area much more quickly. It will be interesting to see how these coils perform over soil once the snow clears here.]

Hi Dan, interesting test. The round tested better for me too, but I still like the rectangle shape. For me the round coil target signal strength was very close out to half the radius off center. I'm wondering how far off center you get before the target detection distance drops below the rectangle detection distance. If you do some more testing.

Thanks green

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Some questions:

1. Does your 'rectangle' coil have semi circle rounded ends or is it a true rectangle?

2: Is your rectangle coil a 3:1 ratio, i.e. three times as long as it is wide?

3. Does your circle or round coil have the same included area as your 3:1 coil?

4. Are your round coil and rectangle coils about the same inductance?

The distances I posted are the greatest I could reliably repeat, so the round coil distances are generally at the center of the coil. I'll have to test the detection distance at the midpoint between the round coil center and the outer edge if I understand your question correctly. The 3:1 oval coil has a very sharp detection 'blade' field at about 2.5" out and beyond, so moving a small distance off of it results in lost detection for very small fast targets. I will test and post a few more 5 to 11 grain dental gold targets when I get the time.

Regards,

Dan

[baum7154]

Just ran an 8.7 grain piece of dental gold and 1st detection is at 4" with solid tone lockup at 3.25" on the 4" X 12.5" oval coil.

Dan

[green]

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Some questions:

1. Does your 'rectangle' coil have semi circle rounded ends or is it a true rectangle?

2: Is your rectangle coil a 3:1 ratio, i.e. three times as long as it is wide?

3. Does your circle or round coil have the same included area as your 3:1 coil?

4. Are your round coil and rectangle coils about the same inductance?

The distances I posted are the greatest I could reliably repeat, so the round coil distances are generally at the center of the coil. I'll have to test the detection distance at the midpoint between the round coil center and the outer edge if I understand your question correctly. The 3:1 oval coil has a very sharp detection 'blade' field at about 2.5" out and beyond, so moving a small distance off of it results in lost detection for very small fast targets. I will test and post a few more 5 to 11 grain dental gold targets when I get the time.

Regards,

Dan

Here is a test I did awhile back. Not sure if what I'm doing compares with your testing. At one inch distance the rectangle was better. Farther out the round coil is better in the center, 25mm and 50mm offset. At 75mm and 100mm offset the rectangle coil was better. The rectangle has round ends, the circumference is about the same as the round coil.

[slowsweeper]

thanks kellogs,hope the field tests go well

[kellogs]

Hi baum7154 great to hear from you i have read your post my understanding the oval coil is best in one application and the round coil in for another we have a few old dis used gold mines and trails not to far out of town up in the mountains that is where i will doing my field test with my round coil.i wont be out for a week or two as went to doctors yesterday and have to get some skin cancers cut out of my left leg and skin grafts any way that what you get for being in the sun as a young bloke.i am going to order some more 26awg tin plated wire teflon coated i was reading a post that some members are using 16 strand Teflon tinned

[baum7154]

Here is a test I did awhile back. Not sure if what I'm doing compares with your testing. At one inch distance the rectangle was better. Farther out the round coil is better in the center, 25mm and 50mm offset. At 75mm and 100mm offset the rectangle coil was better. The rectangle has round ends, the circumference is about the same as the round coil.

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If I understand and calculated correctly the circumscribed area of your round coil is about 314 sq cm.

The circumscribed area of your 265 X 102 mm coil is 243 sq. in. assuming a 50mm end radius.

The round coil has 24% more area than the rectangle coil within it's perimeter. I think this gives the rectangle coil greater flux density/sq. cm. than the round coil.

In Eric's post on rectangular coils he pointed out that 3:1 to 4:1 coil ratios were quite good and that is what I have been investigating with this latest 4 X 12.5" coil that has almost identical circumscribed area to my 8" (7.7") round coil.

All in all it sounds like your tests on round coils are similar.

Thanks,

Dan

[baum7154]

I am interested to hear how your new coil works for you. Good luck with your testing!

Dan

[baum7154]

The following is a re-post of testing of some larger targets from the CHANCE PI BUILD thread because the coil used is the 4" X 12.5" oval discussed in this thread.
-----------------------------------------
These 'small gold targets' are the most difficult I have and are as follows:

1. Gold flakes in glass vial - largest piece is .95 grain, 2 pieces - .19 grain, 1 piece - .12 grain, 1 piece - .11 grain. Total weight of all dust and flakes 2.92 grains. With the flakes loose in a glass vial it is hard to present the target consistently to the coil as the pieces can shift or be on edge.

2. 4.5 grain, 14 kt jewelry gold head for mounting a 4mm stone. No earring post or other metal.

3. 1/4" X 1/4" .004" thick piece of aluminum soda can.

All tests were conducted at a Guard Interval of 10 (8us) on the CHANCE PI detector. Battery voltage throughout the tests was 12.6 volts. Only repeatable test results are accepted in these tests. In many cases greater 1st Detection Distances were observed but not consistently repeatable and so were not included in the results. Test coil was placed horizontal 20" above table and test was conducted in air. Table was slate with no other metal in the area of the coil.

1st Detection Distance Tests:

Target ---------------------------8" Round Coil Distance ---------------------Oval Coil Distance

Gold Flakes ---------------------1.75" -----------------------------------------1"

4.5 gr Head ---------------------4.75" -----------------------------------------3.5"

1/4" X 1/4" AL ------------------4.5" ------------------------------------------2.75"



Solid Detection Tone Distance:

Target -------------------------------8" Round Coil Distance --------------------Oval Coil Distance

Gold Flakes -------------------------0.5" -----------------------------------------.375"

4.5 gr Head -------------------------2.75" ----------------------------------------1.75"

1/4" X 1/4" AL ----------------------2.75" ----------------------------------------1.75"

Conclusion: It is clear that the 8" round coil has a depth advantage but its field is a virtual pinpoint at the greatest distances recorded, making it difficult to quickly cover an area in the field. While the Oval coil has a bit less depth it has an 8" blade like field that will cover an area much more quickly. It will be interesting to see how these coils perform over soil once the snow clears here.

Regards,

Dan[/QUOTE]
---------------------------------------------


These are some additional tests with the 328uh oval coil with 1075 ohm damping on some Aluminum simulators of small gold and some dental gold targets from about 1 gram to a bit over 1/2 gram.

Target--------------------------------1st detection dist------------------Solid tone distance

1/4" X 1/4" X .004" AL------------------2.75"-------------------------------1.75"

3/8" X 3/8" X .004" AL------------------5.5"--------------------------------4.0"

1cm X 1cm X .004" AL------------------5.75"-------------------------------4.12"

1/2" X 1/2" X .004" AL------------------7.5"--------------------------------5.375"

1" X 1" X .004" AL-----------------------11.75"-----------------------------9.75"

.7 grain 1/8" dia AL slug-------------3.25"------------------------------1.75"

1.4 grain 1/8" dia AL slug------------4.25"------------------------------2.375"

2.1 grain 1/8" dia AL slug------------5.5"-------------------------------3.0"

Dental Gold of various geometries and unknown gold percentage.
8.6 grain------------------------------4.5"-------------------------------2.25"

10.6 grain-----------------------------4.75"-----------------------------3.25"

11.8 grain-----------------------------4.25"-----------------------------2.5"

15.4 grain-----------------------------4.75"-----------------------------3.0"

Regards,

Dan

[6666]

I had a try at making the spider coil and it turned out ok
the former was made from MDF board, which is cheap compressed wood fibre board,
cut out with jigsaw.
8 inches.