This week with the recent announcement from Coiltek of the release of their new line of Equinox coils I want to chat to you about Coils both propriety and complementary. How Size actually matters and I address some misconceptions.
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Hey Everybody. Welcome! To Episode 47 of the metal detecting show podcast. My Name is Ciaran and I have been Metal Detecting for nearly 30 Years. This week with the recent announcement from Coiltek of the release of their new line of Equinox coils I want to chat to you about Coils both propriety and complementary.
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Hey Detectorists! Welcome to this week’s episode, So in typical fashion you might remember I said last week. I was ready and made plans to get out during the week but of course the gods of metal detecting decided that my hubris was not warranted and sent a snow storm our way freezing and covering the ground.
at least I’m set up for this week I suppose.
So this week I’m chatting about Coils and as any of our long time listeners will remember I did a Tech Time out on coils all the way back in episode 11 on Night Hawking.
However over the last few weeks there has been a bit of a frenzy online around the new equinox coils from Coiltek, So I decided that we need to revisit the topic in more detail.
An em Coiltek if your listening hook a fella up with a few coils so I can check them out mail already in your inbox..
OK So Coils I have been asked several times over the years about what coil is best to use or should I buy an after-market coil and I always say two things. the first being.
this is a very personnel decision around what type of detecting you do, in what environment, your physical fitness and well-being on and on. Not all coils are created equal just like how all terrains or sites are not equal and you might find that your stock coil performs below expectations on you preferred site if this is the case then by all means invest in another coil. However a behemoth of a 17 inch coil maybe be perfect for your sites however you might not be able to carry it around.
The second advice I always give is say you are better off focusing on learning your detector with the coil that has come with it,
as this coil is what the manufacturers consider the best all round coil for average conditions for your detector
but like I just said previously you may find yourself in a situation where stock is not ideal, so you need to select a coil that is suitable for your own personal situation.
Listen there is a vast body of work covering coil design, inverse square laws and soil resistive components but for us mere mortals it all comes down to a few points.
firstly shape, double D’s or concentric with the second being like everything in this world “SIZE” do you go bigger or smaller.
Before we go onto size ill recap what the differences and advantages are with the coil configurations. with the Double D coil this coil is superior in minerized soil while the concentric coil is superior over the Double d coil in depth and target id.
If you were to dismantle each coil you would find two coil windings one for transmission and one for receive in both. However, In the concentric coil the transmission coil is normally the larger outside coil while the inside smaller coil is the receiver coil.
With a Double D coil both coils are normally the same size but are positioned with the transmission coil on top forming a small overlap with the receiver coil in the shape of a Venn diagram.
What this difference in coil configuration means is that with the concentric coil the full area of the coil has the ability to detect a find while on the double d coil the detection zone is only focused in the areas where both coils cross over as the outer areas form a negative field interference.
Several anecdotes are used to describe the detection field under each coil with the concentric field described like a cone under the coil while the double d coil has a knife-edge detection field
these anecdotes are not technically correct but serve to best illustrated the difference in detection fields.
In reality they are all cones but cones of differing points and radius.
It is because of these differences in detection fields that say for example the concentric is better at target id as it has a wider detection field which can gather more information while the Doube D coil has a narrow detection field allowing better recovery and manoeuvrability between finds.
Normally if your detector comes with a concentric coil it is set up to best operate with a concentric coil and attaching a DD coil might not have the desired effect and this also goes for detectors set up with a dd coil they just won’t work well with a concentric coil.
Some brands have invested heavily in specific coil configurations for example Minelab have doubled down on the double D coil.
Just like configuration most coils come in different sizes with the most common sizes being 6”,11” which is normally the default coil and 17” coils.
Irrespective of the size you go with I really think size is the most important of all specs because it limits the metal detector in very specific ways.
A lot of people believe incorrectly that oh yeah man I got the 17 inch coil and it can goes so deep so much better than my 6 inch coil this is TECHNICALLY incorrect and ill tell you why.
think of the transmission power of your detector as a garden hose of constant pressure and the coil on the detector the hose nozzle.
The smaller the nozzle the more powerful the jet of water produced or at least that’s what it looks like however all that is happening is that the same power is acting on the smaller volume of water pushing at a higher pressure.
Now if you use a larger nozzle it will look slower and less powerful but it will push more volume of water with less pressure now in both scenarios the source power is the same.
This is the same with you metal detector and coil. Where the water pressure is the sensitivity
The smaller the coil the smaller the area covered but the greater the sensitivity
For example the smaller you go with a coil the smaller the nozzle so your pushing the same power but with greater pressure so sensitivity and resolution is better.
with a larger coil or nozzle your water pressure would be a lot less and so is your sensitivity.
Now why did I say that a 17 ich coil doesn’t go deeper well technically a 6 inch coil goes as deep as a 17 inch except that it doesn’t have the cross sectional area on the receive coil to pick up the weak eddy current induced signals from the deeper targets where as the 17 inch coil does so technically a 6 inch can go as deep as a 17in coil but it can’t receive the returning diminished signal so 17 inch coil can only technically receive deeper.
Split hairs much Ciaran..
And remember like in the water hose analogy the pressure is constant And like this the output is essentially constant in your detector.
Any ways a smaller coil has the following advantages and disadvantages
With a smaller coil as I said you get better sensitivity and better response or separation as some people call it.
You have less targets under the coil to cause issues with the target masking.
You also cover less ground but it is also lighter and won’t cause fatigue as much.
With a larger coil you have more perceived depth and you cover more ground so the volume of search area is more however you have less sensitivity you have poorer response or separation. You can potentially can have more targets under the coil which leaves you open for target masking.
Plus they are heavier and cause fatigue quicker resulting in shorter hunts.
A Smaller coil is more suited to trashy sites or a site that requires more manoeuvrability while a larger coil is more suited to wider pastures or clean beach’s with fewer finds.
but here’s the rub with a larger coil you think your covering more ground but your spending more time digging deeper targets and your hunts are shorter due to fatigue, so your not actually covering as much ground as you think I estimate you are actually covering less surface area but more volume looking for bigger targets while missing smaller targets due to reduced sensitivity.
So is a larger coil worth it
if I’m asked by someone who absolutely wants an extra coil but is unsure which to get I always advise on a smaller 6 inch coil first
I just think the benefits out ways any advantage of a larger coil plus they are just more fun
but then inevitably the question comes which brand, do I go with the same brand as my detector or do I go after market and if I go after market which brand do I go with well really you can safely go with any of the long established brands such as Coiltek, Nel or Deteck but if you are going off brand make sure the size of coil you want operates with your detector
but of course most brands provide their own variations of coils sizes but be warned with any extra coils that they are not cheap especially if you go big with some coils costing as much as a simplex about 250 pounds ufff.
Do you have an extra coil for your detector does it make a difference what environment or conditions do you use it with let me know.
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Get out there eyes down and Happy Hunting.