Large coils and actual detecting depth

Just wondering, my current understanding of the Minelab detectors is that they are limited to and may only reach a maximum detecting depth approximating that of an 18 inch round mono coil. In this regard, I know that larger coils can cover a greater surface area (and on the negative side may be heavier, difficult to swing in undulating terrain and are subject to greater EMI), however, do you actually gain much more detecting depth using a (bigger) round mono coil over 18 inches ?

It depends on many factors, but a simple answer if the nugget area is smaller than a 10¢ The answer is no the 18" or smaller is the better choice.

Yes you are right about the larger coil covering more ground, but as geof_junk said the larger the coil the less sensitive it will be on smaller targets. You would be better to use the larger coil in ground that is proven to hold large deep nuggets, such as on old patches that you know have had such large deep nuggets been found. I wouldn't suggest using a larger coil for your every day use as you would find it very tiring after a few hours use. As I said if you are onto a patch that holds large deep nuggets go for it.  My young bloke has been using the 15"x12" Commander mono coil and has been finding some very small deep nuggets with his 5000.  These coils are very sensitive and punch down on deep targets.

Good advice from both Geof & Mike here country girl. Larger coils say 18 inch and above are for just that "larger gold,found at greater depths" but,(and here it comes) the most important thing to consider when searching in any new or old stretch of ground,is "ground coverage",and the more ground one gets to cover over a given period of time,the higher the chances of pinging on to gold,then worry about what other coils would most suit the type of gold you've found and at what depth.I know everyone has or prefers to have a certain comfort level when it comes to an all round preference coil for swinging 90% of the time,by using the standard 11 inch or intermediate class of coil such that mentioned(15x12 or 14 inch round etc)) but,people should not fall into the trap of becoming stereotype complacent,over what one prefers in swinging (because of comfort levels) to what one should be swinging over a certain stretch of ground.The right size coil over the right type of ground conditions,is more important than what we're comfortable with in using 90% of the time.It is wise to use a large coil at the beginning of each days hunt,covering as much surface area as possible,whilst fitness levels are at their highest and change to something smaller when you've had enough.Always allow the ground to do the talking and we to do the walking.  

     Cheers Kon. 

Thank you for your replies. Very helpful information. I agree, the you certainly need the right coil for the right conditions (using the correct technique and optimal detector settings) in order to maximise your gold finds. I usually use small, medium and larger (18 inch round or 24 x 12 elliptical) coils as indicated. I have asked fellow prospectors similar questions (as I will soon re-visit known patches soon - specifically and only looking for deep/larger targets). There still seems to be ongoing confusion regarding the larger coil sizes – as it would seem that there is little depth advantage using coils larger than 18-20 inches (even though they are often marketed as larger coils = more depth). Am I right in thinking that the larger coils are better at detecting bigger objects – but still at the same depth as the 18 or 20 inch coils ? Cheers De

Large coils 20-25in have a distinct advantage over the smaller ones on nuggets 4oz+ and you can get some unbelievable depths on them, that are not attainable with the smaller coils.
But as soon as you go below 4oz your performance drops off in comparison to the smaller ones.

Its all to do with the RX area and the signal strength received back from the target it is all governed by the 'inverse square law' Its a little complex to explain in words without diagrams and I lack the computer skills to make them for you.

So just remember the '4oz' and if you think that there could be a 4oz+ ripper nugget hiding in some deep ground whack the 20 or 25 on and have a crack but you are wasting your time on any thing smaller than this with these larger coils, any smaller and you are better off with the 18 and smaller no matter the soil depth.

Coils larger than 25in (in a mono) are not of much use on any minelab detectors as the pulse is not strong enough to generate the proper magnetic field and the detector will not operate correctly with them.
That's why the trusted coil manufacturers don't make them any larger than 25in and you will only find them being made and sold by shonky manufacturers.
Also have a read of this link:
https://golddetecting.forumotion.net/t18080-fine-gold-v-enhanced
We were talking about depth on larger targets in this post a few weeks ago.
And also use the search function as this subject has been covered many times and there is a wealth of knowledge just one search away  

Aurumpro wrote:

Its all to do with the RX area and the signal strength received back from the target it is all governed by the 'inverse square law' Its a little complex to explain in words without diagrams and I lack the computer skills to make them for you.

So just remember the '4oz' and if you think that there could be a 4oz+ ripper nugget hiding in some deep ground whack the 20 or 25 on and have a crack but you are wasting your time on any thing smaller than this with these larger coils, any smaller and you are better off with the 18 and smaller no matter the soil depth.

Coils larger than 25in (in a mono) are not of much use on any minelab detectors as the pulse is not strong enough to generate the proper magnetic field and the detector will not operate correctly with them.

What do you think this issue would equate to regarding DD coils? Don't mean to hijack the thread, but it seems to me that the 11" round mono is the perfect size for the amount of power these machines are allowed to use. A 11" round would be the best "deep" nugget coil imo, but only with monos. DD sadd another twist to this, don't they?    

Shinegold wrote:

Aurumpro wrote:

Its all to do with the RX area and the signal strength received back from the target it is all governed by the 'inverse square law' Its a little complex to explain in words without diagrams and I lack the computer skills to make them for you.

So just remember the '4oz' and if you think that there could be a 4oz+ ripper nugget hiding in some deep ground whack the 20 or 25 on and have a crack but you are wasting your time on any thing smaller than this with these larger coils, any smaller and you are better off with the 18 and smaller no matter the soil depth.

Coils larger than 25in (in a mono) are not of much use on any minelab detectors as the pulse is not strong enough to generate the proper magnetic field and the detector will not operate correctly with them.

What do you think this issue would equate to regarding DD coils? Don't mean to hijack the thread, but it seems to me that the 11" round mono is the perfect size for the amount of power these machines are allowed to use. A 11" round would be the best "deep" nugget coil imo, but only with monos. DD sadd another twist to this, don't they?    

the same Inverse square law of diminishing response apply to them too mate but the Rx area of the coil is halved.
Its all to do with the Rx.
Simple mathematics really..........

No not exactly right De.More like a tricky form of misguided advertising.Do larger coils go deeper than smaller coils do?,the answer to that question is yes,depending on the size of the target.If anyone here were to do some testing,say between the 11 inch mono 14 and 18 inch,they'll soon come to realize that the depth advantage gained,by testing say over a 1 ounce slug of gold,would be about +/- 2 inches gain,between each coil.This law basically applies right up to an 18/20 inch coil size.Jump to a 25 inch coil and above and you'll find yourself gaining little or no depth advantage over the 18 inch coil in depth,over that same oz slug.If the slug of gold were to jump in size,to say a 5oz and above,this is where you'll gain greater depth advantage,by using the larger 25 inch mono,over the 18 or 20.There is a detector/coil field power cut-off point and people should not be made to believe that by doubling the coil size diameter,you double the depth on the same size target,for this is far from the truth.
The larger the object,the deeper it will be detected by say a 25 inch coil for example,over that of an 18 inch coil.
Larger coils are not better at detecting bigger objects than smaller coils,they are better at detecting bigger/larger objects at greater depth,than that of smaller size diameter coils.As target size increases,so will the depth advantage increase by using say a 25 inch round coil for example,over that of an 18/20 inch coil.Where the depth advantage remains pretty much the same or on par between an 18/20/25 inch coil,is only on a certain size given target. Confused,good,so am I.

    Cheers Kon. 

Thank you Kon and Aurumpro (and everyone) - it makes perfect sense. Cannot wait to use a bigger coil on my favourite areas. Your information will be helpful to everyone. Cheers De