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Thread: Is there really an advantage to a DD coil????

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  1. #1

    Jan 2013
    10
    1 times
    All Types Of Treasure Hunting

    Is there really an advantage to a DD coil????

    I've read about the advantage of using a DD coil such as what came on my new E-TRAC but this makes me wonder. Here is a simple illustration showing the advantage in trashy areas but...why does my coil give a signal along the left or right edge of the coil without a target not even passing close to the middle?
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  2. #2
    ru
    Jan 2013
    Russia, Nizhny Novgorod
    MINELAB X-Terra 705
    11
    10 times
    All Types Of Treasure Hunting
    If you are able correctly to understand VERY LONG machine translation. I can quote one post on this subject from a Russian-speaking forum. This message seems to me very full.
    Quote beginning

    For beginners about Mono and DD coils

    ice message" 09 Feb 2010, 15:37:41
    Let's try to consider in general these two types of coils for acquaintance
    In the theory a difference between mono and DD as you understand in construct and tactics technical characteristics. at mono coils the beam goes a cone from all plane, and at DD as though an edge through its center, from here...

    Mono pluses in comparison with DD:
    It is more than depth at cone peak, that is 10" mono coils on the center takes just as bigger 12" DD, but to edges of the coil depth at Mono sharply falls
    Better purpose identification, that is any party to the purpose the will be identical. But we won't forget that if the purpose masking by ferrous metal, it is necessary to scan it from all directions, it isn't dependent on coil type
    Better purpose centering at detection of exact location of a find

    The DD pluses in comparison with Mono:
    Stable depth on all length of the coil, that is it is more stable - the productive area of scanning, it is less than admissions
    Stabler work and depth on the mineralized soil

    General minus Mono and DD:
    At increase in the size of the coil more than about 14 inches start worsening identification and sensitivity to the small purposes, coil unstable work raises

    It everything in the theory, well and in practice we have full mess connected most likely with the concept "successful model" and "not successful model" of the coil of a line of firm of the producer. On this practician and responses of colleagues you shouldn't ignore, but also laws of physics who didn't cancel

    I will try to bring the IMHO:

    for search on the platforms littered by iron it is better to choose small 6" the Mono coil
    for investigation and primary search on a platform it is necessary 10DD or 12 of DD
    for a deep doborka (hunting behind that remained from those who was earlier) of the empire on rather pure place it is necessary big Mono or DD, the size from 12 inches to 15”
    If you don't dig on war, be not fond of big "wheels"

    As there is a distinction of coils in a form - round and an ellipse. Ellipse it is more convenient on a dense grass, in a bush, between trees. In certain cases smaller number of the purposes in coil capture

    Well here in brief something like this, certainly there are many subtleties in certain conditions of search and personal preferences, for example in a postscoring, play not the last role, but I think that I described the general rules. If is what to add - that guys will add me

    The detector X-Terra 705 can function
    on various transmission frequencies with coils,
    compatible to the VFLEX technology.

    Concentric standard frequency (7.5 kHz)
    This frequency is suitable for search more
    main objectives on the main types of the soil. On
    these the coil is available a sticker of M.

    Concentric Low frequency (3kHz)
    This frequency is suitable for search more
    the large purposes at a bigger depth, and coins with
    high conductivity (majority of coins
    The USA), such coils reject signals better
    from ferrous metals. On them there is a sticker
    L.

    Concentric High frequency (18.75 kHz)
    This frequency is suitable for search more
    the small purposes at a surface, gold
    nuggets and the purposes with low conductivity
    (stamping coins, small jewelry). On
    these the coil is available H sticker

    Double D (7.5 kHz and 18.75 KHZ)
    By means of these coils the detector is better
    adjusts balance of soil. They it is ideal
    are suitable for search of gold nuggets in
    to the the strongly mineralized soil or on
    beaches with magnetitovy sand
    Quote end
    If something isn't clear - please ask
    Last edited by Sever; Jan 23, 2013 at 06:58 AM.
    I ask to forgive for my English. I write with the dictionary.

  3. #3

    Jul 2012
    Holmes County Ohio
    Tesoro Lobo
    1,433
    901 times
    All Types Of Treasure Hunting
    So...your question is why you get a signal before your coil is directly over the target?

    Is this really a problem? Turning your sensitivity down might help, but if you are hunting trashy areas, a small coil is what you need.

    Good Luck.
    Two rules in life: Don't sweat the small stuff.

    It's all small stuff.

  4. #4
    us
    May 2012
    Florida
    Minelab Safari Minelab X-Terra 305
    230
    71 times
    All Types Of Treasure Hunting
    I think the OP is having the same issue I seem to be having with my Safari. I'll get a hit on say the right side of the coil, then as the center passes over it, it disappears. Swinging back towards the left side of the coil, the same thing however, further to the left of the original hit. Attempting to pinpoint with the coil, its as if the coil is between two targets. I've spent up to 30 mins on an area like this where nothing seems to change even after digging about a 3 foot circle and down up to 15". Usually fustrastion sets in and I fill in the hole and move on. Living close to KellyCo, I have considered taking it in for a check up to see if it's the machine.

  5. #5
    us
    TH'ing Philatelist

    Sep 2012
    Bloomington Indiana
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    I have always had some trouble pinpointing with DD coils. Hoping when it warms up I can finally get enough practice in to be proficient (eventually)
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  6. #6

    Jan 2013
    10
    1 times
    All Types Of Treasure Hunting
    Quote Originally Posted by Gold Maven View Post
    So...your question is why you get a signal before your coil is directly over the target?

    Is this really a problem? Turning your sensitivity down might help, but if you are hunting trashy areas, a small coil is what you need.

    Good Luck.
    No my problem is the DD coil is supposed to be better in trashy areas because of the narrow beam that shoots down the center of the coil from front to back. If you look at the illustration you see the nail on the edge of the coil not being in that beam. It doesn't really seem to work that way. My coil will pick up a nail on the very edge of the coil.

  7. #7
    Charter Member
    us
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    Jul 2006
    Orlando, Fl
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    What detector are you using and what coil, what size?

    I have been using DD coils for 5 years and love them. I use Minelabs so I don't have to be concerned about Iron and mine do give me signal on targets off the edge of the coil, I consider that a bonus.

    You may want a smaller coil, hard to say since don't know size your using....

    A good way to learn to pinpoint with DD is tape a coin or couple coins on a large piece of cardboard turn it over and flip it on ground where you have removed all signals and pinpoint the coins, try it with a nail and coin and see the difference, play with it with different targets, the larger the cardboard the better.




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  8. #8

    Jan 2013
    10
    1 times
    All Types Of Treasure Hunting
    Quote Originally Posted by Treasure_Hunter View Post
    What detector are you using and what coil, what size?

    I have been using DD coils for 5 years and love them. I use Minelabs so I don't have to be concerned about Iron and mine do give me signal on targets off the edge of the coil, I consider that a bonus.

    You may want a smaller coil, hard to say since don't know size your using....

    A good way to learn to pinpoint with DD is tape a coin or couple coins on a large piece of cardboard turn it over and flip it on ground where you have removed all signals and pinpoint the coins, try it with a nail and coin and see the difference, play with it with different targets, the larger the cardboard the better.
    I'm using the stock 11" pro coil that comes on the E-TRAC. I have no problem pinpointing with it, it is just the fact that it doesn't really have that narrow field of detection that it's advertised to have that kind of bothers me.

  9. #9
    Charter Member
    us
    Big Boys Hobbies

    Jul 2005
    Moore Oklahoma
    Call for your Treasurenet special discount! Be sure to mention Tnet when you call!
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    Quote Originally Posted by robertj298 View Post
    I'm using the stock 11" pro coil that comes on the E-TRAC. I have no problem pinpointing with it, it is just the fact that it doesn't really have that narrow field of detection that it's advertised to have that kind of bothers me.
    What your experiencing is true with all DD coils, not just Minelabs. If the target is shallow it will hit 3 times. Once for each side of the coil. Deeper targets will get one solid signal for the center of the coil. It is a GREAT way for a quick fast and dirty way to gauge depth.



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  10. #10

    Jan 2013
    10
    1 times
    All Types Of Treasure Hunting
    Quote Originally Posted by Bart@Big Boys Hobbies View Post
    What your experiencing is true with all DD coils, not just Minelabs. If the target is shallow it will hit 3 times. Once for each side of the coil. Deeper targets will get one solid signal for the center of the coil. It is a GREAT way for a quick fast and dirty way to gauge depth.
    My point is not that it isn't a great way to gauge depth or isn't a good coil, my point is it doesn't seem to have the narrow field of depth shown in the ad. I pictured, showing a nail not being detected at the same time as a coin is.

  11. #11
    us
    Crazy 'Ol Foole

    May 2012
    Backside Of Nowhere In Mid-Michigan
    Fisher F2, Fisher 1280X, MineLab Xterra 705, MineLab Explorer SE
    664
    317 times
    All Types Of Treasure Hunting
    Soil conditions, target content, and speciffic coil design all play roles in what you're describing. Wet ground will conduct better. Iron and zinc leach into the soil. And some coils are designed to be wider or narrower patterns.
    There's likely nothing wrong with the coil. If there was, it would either false all over the place or simply not function at all.

    And FWIW, that illustration is just theoretical and generic.
    Last edited by Longhair; Jan 23, 2013 at 06:49 PM.

  12. #12
    us
    Oct 2010
    eastern wa
    minelab eureka,fisher f2,ace 150,fisher gold tick,whites coin classic II
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  13. #13
    us
    Oct 2009
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    Quote Originally Posted by robertj298 View Post
    No my problem is the DD coil is supposed to be better in trashy areas because of the narrow beam that shoots down the center of the coil from front to back. If you look at the illustration you see the nail on the edge of the coil not being in that beam. It doesn't really seem to work that way. My coil will pick up a nail on the very edge of the coil.

    No, no, no! You are confusing the theoretical response zone with the reality. Very shallow targets will hit on the edges and the middle.

    Here is the truth....

    DD coils are made from two overlapping rings. Each ring puts out a donut shaped EM field. This give the strongest response down the center but doesn't mean it's the only spot you can recieve a target response.

    DD and concentric coils both have advantages and disadvantages. They are tools. Pick the one that best fits your needs for that hunt.
    Last edited by Jason in Enid; Jan 23, 2013 at 07:18 PM.
    Longhair likes this.

  14. #14

    Jan 2013
    10
    1 times
    All Types Of Treasure Hunting
    Quote Originally Posted by Jason in Enid View Post
    No, no, no! You are confusing the theoretical response zone with the reality. Very shallow targets will hit on the edges and the middle.

    Here is the truth....

    DD coils are made from two overlapping rings. Each ring puts out a donut shaped EM field. This give the strongest response down the center but doesn't mean it's the only spot you can recieve a target response.

    DD and concentric coils both have advantages and disadvantages. They are tools. Pick the one that best fits your needs for that hunt.
    Thats what I thought. The posted theoretical response zone is really false and misleading making one believe that a shallow nail will not be in the response zone while a coin in the middle will be.

  15. #15
    us
    Oct 2009
    4,785
    2147 times
    All Types Of Treasure Hunting
    That's because it would be far to confusing for most customers if the manufacturers tried to explain the realities of detector coil EM fields. Simple graphics which are MOSTLY true are "good enough".

 

 
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