northwest How can all of this be achieved with a mono coil?
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australian electronic gold prospecting forum.com  |  Detector Technology and Electronics and new detectors  |  Detector Coils  |  Topic: How can all of this be achieved with a mono coil? 0 Members and 1 Guest are viewing this topic. « previous next »
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Author Topic: How can all of this be achieved with a mono coil?  (Read 1762 times)
Doug
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« on: Friday April 24 2015 20:38:03 AEST PM »

How can all of this be achieved with a mono coil?
Coiltek are coming out with a new 14” mono  next week that they claim (and some who have tested prototypes see to confirm) that will have very significantly improved sensitivity and depth  to small gold in particular. The coil is apparently quite heavy which suggest more windings= higher tx field strength In view of the fact that ML detectors need coils with a inductance of about 300uH and a low  resistance how can all of this be achieved in this new mono as the inductance increases as the square of the number of turns? L= (d^2 * n^2)/(18d+40l)  for an air core inductor? If the coil has more windings its efficiency as an antenna will also be improved  including to EMI and ground mineralization?The coil its reported still uses litz wire.
L is inductance in micro Henrys,
d is coil diameter in inches,
l  is coil length in inches, and
n is number of turns.
  
  
  
Ideas?
doug smile
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« Reply #1 on: Saturday April 25 2015 04:19:48 AEST AM »

Hi Doug,

It may be a mono coil in name only. 

There's a simple way to decrease the sampling delay.  It's an old idea that was used in the military
mine detectors.  Only the firing pin is metallic and to detect it, the sampling pulse must get very
 close to the trailing end of the coil pulse.

It's the inductance of the receiving coil that determines the required sampling delay. As you point
out, the inductance is proportional to the square of the turns.  The target signal amplitude however,
is proportional to the turns.

Therefore, two smaller cois with the same total number of turns and the same total area yield the
same signal amplitude with only half the inductance.  (The interaction between the coils modifies
that a little.)  This increases the sensitivity to targets with short time constants, but leaves the
sensitivity to large, solid targets unchanged.  Isn't this what we're seeing with the ZED?

"Everything old is new again..."

Prospector_Al
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Doug
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« Reply #2 on: Saturday April 25 2015 10:54:33 AEST AM »

  
Hi Doug,

It may be a mono coil in name only.  

There's a simple way to decrease the sampling delay.  It's an old idea that was used in the military
mine detectors.  Only the firing pin is metallic and to detect it, the sampling pulse must get very
 close to the trailing end of the coil pulse.

It's the inductance of the receiving coil that determines the required sampling delay. As you point
out, the inductance is proportional to the square of the turns.  The target signal amplitude however,
is proportional to the turns.

Therefore, two smaller cois with the same total number of turns and the same total area yield the
same signal amplitude with only half the inductance.  (The interaction between the coils modifies
that a little.)  This increases the sensitivity to targets with short time constants, but leaves the
sensitivity to large, solid targets unchanged.  Isn't this what we're seeing with the ZED?

"Everything old is new again..."

Prospector_Al

Thanks. Your explanation may explain why the new coil is apparently so much heavier. You are right about the ZED! It appears to give no more depth than previous models on long TC nuggets!
doug smile
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« Reply #3 on: Saturday April 25 2015 11:12:42 AEST AM »

The in - ground depths on short TC targets that I have read on other forums that the GPZ is producing far exceeds the air - testing results that I have done with my GPX and Mono coils on small nuggets.

Such in- ground depths as 0.6 gram nugget at 13 inches and 3.5 gram specie at 20 inches both said to be measured and dug carefully.

Also spoke to someone by phone whose friend dug a 3 gram nugget at 19 inches, again said to be dug and measured carefully.
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« Reply #4 on: Saturday April 25 2015 11:19:57 AEST AM »

  
The in - ground depths on short TC targets that I have read on other forums that the GPZ is producing far exceeds the air - testing results that I have done with my GPX and Mono coils on small nuggets.

Such in- ground depths as 0.6 gram nugget at 13 inches and 3.5 gram specie at 20 inches both said to be measured and dug carefully.

Also spoke to someone by phone whose friend dug a 3 gram nugget at 19 inches, again said to be dug and measured carefully.

I  thought i read on 4 umer that the .6 grams at 13" was using a prototype  coiltek elite mono?
doug smile
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« Reply #5 on: Saturday April 25 2015 11:26:39 AEST AM »

  
I  thought i read on 4 umer that the .6 grams at 13" was using a prototype  coiltek elite mono?
doug smile

It was mentioned in the thread GPZ my rating 4 out 10 on that forum.
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« Reply #6 on: Saturday April 25 2015 12:19:08 AEST PM »

Going by some in-ground tests with a GPZ, which as I recall were posted here and on other forums, showed it detected a 0.7 gram nugget at 7.5 inches and a 3.5 gram nugget at 12 inches.

These depths are nearer to what I can achieve in an air-test on a 0.8 gram and a 4 gram nugget with my GPX and a 12 inch mono coil.

Nuggets and Species can vary greatly in shape, purity and surface area but the in-ground depths being stated by others with a GPZ are significantly above the GPZ in-ground test results that I am speaking about.

I very much doubt the new Coiltek 14" Mono coil on a GPX will make up the difference on small nuggets if we are to  believe the in -ground depths being stated by owners of a GPZ with its 14" DOD coil.

However if the in- ground depths in the test results I speak about in my first sentence of this post, are closer to the what the GPZ can achieve, then maybe a new type of mono coil can create more depth for the owner of a GPX and get closer to the GPZ on smaller nuggets.

Edited due to Spelling Errors
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« Reply #7 on: Saturday April 25 2015 12:35:46 AEST PM »

  
Going by the some in-ground tests with a GPZ, which as I recall were posted here and on other forums, showed it detected a 0.7 gram nugget at 7.5 inches and a 3.5 gram nugget at 12 inches.

These depths are near to what I can achieve in an air-test on a 0.8 gram and a 4 gram nugget with my GPX and a 12 inch mono coil.

Nuggets and Species can vary greatly in shape, purity and surface area but the in-ground depths being stated by others with a GPZ are significantly above the GPZ in-ground test results that I am speaking about.

I very much doubt the new Coiltek 14" Mono coil on a GPX will make up the difference on small nuggets if we are to  believe the in -ground depths being stated by owners of a GPZ with its 14" DOD coil.

However if the in- ground depths in the test results I speak about in my first sentence of this post,are closing to the what the GPZ can achieve, than maybe a new type of mono coil can create more depth for the owner of a GPX and get closer to the GPZ on smaller nuggets.

Thanks for the clarification. However you do not need a special mono coil to have sensitivity to small  gold. I know of an experimental Pi detector that can sample at 10 usecs with an 18" NF mono at a peak coil current of about 3.5 amps and detect a .2 gram nugget at several inches in air tests and  detect some longer TC targets beyond the range of the gp/gpx!
doug smile
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« Reply #8 on: Saturday April 25 2015 15:52:47 AEST PM »

  
  
Going by the some in-ground tests with a GPZ, which as I recall were posted here and on other forums, showed it detected a 0.7 gram nugget at 7.5 inches and a 3.5 gram nugget at 12 inches.

These depths are near to what I can achieve in an air-test on a 0.8 gram and a 4 gram nugget with my GPX and a 12 inch mono coil.

Nuggets and Species can vary greatly in shape, purity and surface area but the in-ground depths being stated by others with a GPZ are significantly above the GPZ in-ground test results that I am speaking about.

I very much doubt the new Coiltek 14" Mono coil on a GPX will make up the difference on small nuggets if we are to  believe the in -ground depths being stated by owners of a GPZ with its 14" DOD coil.

However if the in- ground depths in the test results I speak about in my first sentence of this post,are closing to the what the GPZ can achieve, than maybe a new type of mono coil can create more depth for the owner of a GPX and get closer to the GPZ on smaller nuggets.

Thanks for the clarification. However you do not need a special mono coil to have sensitivity to small  gold. I know of an experimental Pi detector that can sample at 10 usecs with an 18" NF mono at a peak coil current of about 3.5 amps and detect a .2 gram nugget at several inches in air tests and  detect some longer TC targets beyond the range of the gp/gpx!
doug smile

A .08 gram "nugget" can be detected at 2"-3" and a 5 cent piece at roughly 17"-18"
doug smile
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« Reply #9 on: Saturday April 25 2015 16:31:49 AEST PM »

  
I A .08 gram "nugget" can be detected at 2"-3" and a 5 cent piece at roughly 17"-18"
doug smile

Goodness are these results with an 18" mono on this said experimental detector?
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« Reply #10 on: Saturday April 25 2015 17:02:52 AEST PM »

happy face This sounds like an Eric Foster stacked coil to me we have been testing this coil of late and my inital findings are very impresive but I have yet to try it with a minelab detector. happy face
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« Reply #11 on: Saturday April 25 2015 17:08:54 AEST PM »

  
  
I A .08 gram "nugget" can be detected at 2"-3" and a 5 cent piece at roughly 17"-18"
doug smile

Goodness are these results with an 18" mono on this said experimental detector?

Yes.
doug smile
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« Reply #12 on: Saturday April 25 2015 17:11:56 AEST PM »

Eric Foster has made monumental contributions to "the art".
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« Reply #13 on: Saturday April 25 2015 17:15:23 AEST PM »

  
happy face This sounds like an Eric Foster stacked coil to me we have been testing this coil of late and my inital findings are very impresive but I have yet to try it with a minelab detector. happy face

IBGold if you ever want another independent tester to test a coil of yours let me know and I would be privileged to do so on my GPX5000.
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« Reply #14 on: Sunday April 26 2015 11:00:52 AEST AM »

  
happy face This sounds like an Eric Foster stacked coil to me we have been testing this coil of late and my inital findings are very impresive but I have yet to try it with a minelab detector. happy face

Maybe a stacked Coaxial coil which I have read Eric say has less ground feedback than a mono since the TX coil is separated by a vertical distance from the bottom RX, which is close to the ground as the surface mineralisation that gives the greatest signal variations with coil type.

Eric says mineralisation at depth (6in or more down) gives less change in signal between coil types. Also he says increasing the separation in a Coaxial coil will reduce ground effect, and also the signal, as the TX gets further away. The signal from a small object will decrease faster than the ground so there is no advantage here.

Therefore I assume the vertical separation distance between the Tx and Rx coil is most important to retain sensitivity to small nuggets but what effect on larger nuggets?
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« Reply #15 on: Monday April 27 2015 11:11:16 AEST AM »

 On another forum its speculated that the  Coiltek elite coil uses braided litz wire like the 7000 DOD Tx.
doug smile
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« Reply #16 on: Wednesday June 24 2015 08:33:44 AEST AM »

I have one of the new CoilTek 14" Elite Mono coils and am interested to know if it is "new technology".

It certainly is sensitive and I just yesterday picked up a single shotgun pellet at about 2" at Mt Crawford. I also dug a foil pouch out of newly turned soil for tree planting, down past 2 feet. The coil picked up the pouch when waved a well above the surface of the soil. Ever hopeful one day these massive signals will materialise into a large nugget  happy face

It gives nice sharp responses and behaves a lot like a smaller coil on steroids. I have noticed and it has also been pointed out to me by others that the left side of the coil is a little more sensitive than the RHS. It also has a sensitive "toe" and "heel" hot spot for testing your recovered target over.

Anyone yet know if its 2 smaller coils acting as one as has been suggested above?

Ian
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« Reply #17 on: Thursday June 25 2015 06:38:40 AEST AM »

  
Maybe a stacked Coaxial coil which I have read Eric say has less ground feedback than a mono since the TX coil is separated by a vertical distance from the bottom RX, which is close to the ground as the surface mineralisation that gives the greatest signal variations with coil type.

Eric says mineralisation at depth (6in or more down) gives less change in signal between coil types. Also he says increasing the separation in a Coaxial coil will reduce ground effect, and also the signal, as the TX gets further away. The signal from a small object will decrease faster than the ground so there is no advantage here.

Therefore I assume the vertical separation distance between the Tx and Rx coil is most important to retain sensitivity to small nuggets but what effect on larger nuggets?

Maybe this is a stupid question, but what if the tx power can be reduced or tailored for a particular ground ? Couldn't you in theory get better signal returns ?

Also on other comments in this thread, Razorback make folded monos which display good pinpointing in the toe of the coil.
And I have read sdc users mentioning pinpointing with the sdc coil, something about the 11 o'clock position....
Also recently read something about the new coil, where it was felt sensitivity was greatest on the side opposite the cable gland/exit.
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« Reply #18 on: Thursday June 25 2015 07:04:17 AEST AM »

Aziz did a lot of work to show with tables and his coil software, how to make better mono coils.

Theres a whole lot of info and graphic illustrations. Heres a couple of links to that thread.

  !/msg32055/#msg32055

  !/msg32076/#msg32076
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« Reply #19 on: Thursday June 25 2015 20:56:58 AEST PM »

And Stefan spoke about reducing capacitance in coils, even earlier in time. Here is a quote from him...

" I place 4 turns on the first layer then place a spacer and then wind another 4 turns etc. This way you get a rectangular coil. The reason for the spacer is to minimise the interwinding capacitance between the layers."

His full post on this can be found here :   
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