Are Big Coils Worth It?

[GB_Amateur]

I doubt I'm the first to wonder about this or even to start a thread here on the subject.  But there is a lot of fuzziness regarding this issue and I'm considering purchasing yet another coil so I'd like to get some expert opinions (yes, that means you, detectorprospector reader :).

You can break searchcoil size into any categories you see fit, so I'll start with mine.  First off, coils don't need to be circular or axially symmetric and many are far from it.  But to simplify let's use the larger of the two axes as the nominal size.  I divide into three categories:  small = {coils whose larger dimension is less than 7 inches ~ 180 mm}, medium = {coils with larger dimension between 7 inches and 12 inches ~ 300 mm}, and large which are all coils with larger dimension greater than 12 inches.

Selfishly I'm going to ignore the first two categories since I have several of these for my two detectors.  My question comes down to:  "Should I get a big coil?"  Certainly you'd like to know my detecting requirements so here they are.  In order of priorities:  1) nugget hunting (high), 2) coin hunting (moderately high), 3) ghost towning &/or typical historic site relic hunting (moderate).  I leave off many areas that interest other detectorists relish:  {beach combing, underwater recovery, battlefield relic hunting, cache hunting, etc.}.

Looking online, both at text reviews and reports plus YouTube videos, there seems to be support/evidence/hype? that large coils go deeper to find coins (in particular) at hunted out sites.  Being someone who successfully coin hunted 45 years ago with what today wouldn't even qualify as a child's detector (Heathkit T/R with no ground balance and no discrimination) I can add my name to the list who understand that finding old (pre-clad, pre-Lincoln Memorial) is an uncommon experience today.  But back to the issue, here are the pluses and minuses I see with large coils.  Disadvantages:

1) heavy (although maybe not so ridiculous if you lug around one of the many PI heavyweights),

2) noisy, in terms of more mineralized ground within the coil's zone of influence, potentially picking up more trash signals, and higher sensitivity to RF background interference,

3) loss of sensitivity to small/tiny targets, particularly small gold nuggets but also small jewelry,

4) cost.

Contrast that to the advantages:

a) bigger sweep swath,

b) deeper detection sensitivity.

I know it's still difficult to quantify since there are so many variables to weigh.  But what is your experience?  Do you use the large coils you've bought or have you reverted to the medium and small coils, leaving the large ones in your museum displays?

[fredmason]

much depends on which detector you are using.  I use big coils for ground coverage and  relative increase in depth. The deepest target I ever dug with my 3500 was detected with an 11 inch stock mono coil...about 30 inches and was just a whisper. For park hunting I generally use my 6 ich ctx coil. I used many large coils on various Minelab Pi's and they all found something. The biggest and heaviest was a 24 inch coiltek DD...that was long before the hipstick was born. My gb2 always had the small e-coil...

I use a GPZ now and do not think I will be buying the new 19 inch...never say never!

fred

[Ridge Runner]

If it wasn't a lot of money made off coils it wouldn't be so many to choice from. The other factor is we think and want what we think will find more for us. I say us but I'm wanting only what's best for me. Then every coil company is telling you what they got is the best money can buy. This is where we all get our self in trouble because one has to buy to know the truth. Before can't live without and after can't live with it.

Just remember it's only money and your not going to take it with you. So I say spend it here on a coil. I got one I'm thinking about now.

Chuck 

[californiagold]

I think a detectorist that spends an adequate amount of time detecting annually,  should consider having a big coil in their arsenal.  If someone only detects a couple times a year, then I wouldnt consider it. Alot for me would depend on what detector it was for. I think most brand big coils for vlfs probably average about 1-2" more depth then a 7-11" coil. but that amount of increase might just make a difference at certain places and scenarios.  The big coil might brighten up a quiet signal that was just missed with a smaller coil. I think the best one out of several that I tried for vlfs was made by Nel coils. but that was on a gb pro. I usually use a 10" for scout detecting at a new site. it is a good in between size that will grab small and bigger targets. then ill switch to another size depending on the size of the targets that im after. With pi detectors I feel I get alittle more depth with a big coil over the standard 11" on targets. More then the 1-2" increase from vlf big coils. the big coils on any detector do have the advantage of faster ground coverage though. so basically it is good to have several size coils for different situations if you spend enough time in the field to be worth the purchase.

Good luck

[Steve Herschbach]

The primary reason for my using larger coils is usually for better ground coverage first and more depth second. My Bigfoot coil is a perfect example of using a large coil for ground coverage because at only 3" wide it is not a deep seeking coil. Can't beat it for sports fields or large parks areas though. And it is looking like the 17" coil for my CTX will be the coil most used at the beach, for no other reason than that beaches are huge and finds can be sparse. Ground coverage first, and depth gain a bonus.

For most coin detecting I prefer stock coil sizes or smaller. I tend to gravitate to trashy locations so target separation is usually a factor. Plus, in a lot of mineralized areas the depth gains if any are minimal with larger coils when running VLF detectors. If the ground is bad enough you can get actually get less depth with a larger coil on a VLF due to ground feedback.

For PI type nugget detecting I do often lean towards larger coils, but now a bit more for depth than ground coverage. You get more bang for the buck with large coils on a PI than on a VLF. My standard coil for my GPX 5000 the last few years I had it was an 18" round mono coil.

When I add it all up over the years however I have to admit that overall gains from larger coils for anything other than a PI are often more imagined than real, and many oversize coils I have purchased got minimal use once reality set in. I have therefore become a bit more cautious of investing in larger coils as I have usually had better returns with smaller coils. I do think they are worth having but with the realization that they often end up as niche items that only get use on rarer occasions. Once of the nice things about selling my GPX was in getting rid of all those coils!!

Right now I only have three I am keeping:

18" x 3" Bigfoot coil for DFX - sweeping large areas like sports fields for jewelry; ground coverage

15.5" x 13" DD for Gold Racer - looking for large nuggets in cobble piles; depth

17" x 13" DD for CTX 3030 - beaches, other large areas with sparse targets; ground coverage, depth

 Big coils worth it? Yes, but only for very specific uses.

[Roughwater]

3 hours ago, Steve Herschbach said:

For PI type nugget detecting I do often lean towards larger coils,

You know most ground you will be on will likely have been pounded by detectors.  Assuming most of the shallower easier to find nuggets will be gone, I have to think either a very large coil or a very sensitive coil would be the better options.  A coil to either get you the deeper smaller pieces or the deeper larger pieces.  Of course you will want the very large coils to get you the deeper larger nuggets or a very sensitive coil with a detector to get those smaller bits.  I'm thinking the 6-8" Minelab or Coiltek round coils, or maybe the new 9-14" Nuggetfinder Evolution,  the similar coiltek blitz as well as the Joey or Sadie on or the newer round 11" coiltek mono elite on the smaller end.  On the larger end the New 14" coiltek mono elite, the New 17X13 Nuggetfinder Evolution, the 18" coiltek mono elite and the larger mono coils to and beyond the 25" round. I think at least one smaller and one larger dd coil would be a good choice too if you run into tough ground or EMI.  Some of the newer higher tech coils suggest promise of being both deep and sensitive so which is why I listed some of them.  I have as a back up a Eureka gold and I have several coils including the little 6" coiltek which I hope will give me the sensitivity to find the tiny dinks among the iron.

  

[GB_Amateur]

Thanks for all the well thought out responses.  I decided to go ahead and get a NEL Attack coil for my Fisher GB Pro (also works for the Teknetics Frat Brothers), used from Ebay.  I'm still getting acquainted with the White's TDI/SPP detector so will wait there, although I do have a 9X14 Garrett Infinium Mono in the shop, trying to mod it to work with the TDI.  I'll report if I accomplish that task, but don't hold your breath as it isn't on the top of my detecting hobby to-do list at the moment, and it's far from my skill set level of expertise (but it's still fun trying!).

 

[RickUK]

I have a fair few larger/very large coils for both VLF and PI machines,my main aim is depth here in the UK and not necessary ground coverage,the targets that i am after are old artifacts,scattered coin hoards and locating the actual hoard container itself.One has too step back and think what my targets are and why are they deep ??

Our history in the UK goes back 1000s of years,way before banks or other secure ways of holding coins or artifacts of great value,the only way for many hundreds of years was basically hiding these valuables in the ground or secure locations,as a baseline depth of a man laying down and depositing the hoard at arms length in the hole and then of course back filling it again,hoping to come back after the war,skirmish,plague or what ever the reason for hiding it.

So most detectors either VLF or PI with a standard coil on would struggle to hit these deep targets,so this is the reason i do own some big coils for some of my VLF and PI machines,for the most part the maximum size for a VLF detector is about 15'' as it appears to striggle to gain extra depth due to the dynamics on how these machines work,PI detectors can run a bigger coil and hence why i have s election for both types of machines.

Not only do i hanker for the depth but also on some sites the ground conditions dictate ie minerals and trash which machine i would use,if its a trashy site then i would use a machine that has some form of discrimination on it,

My main VLF machines and coils selection for these types of hunting conditions are:

T2 with NEL 14x13 Storm and BIG Nel 17x15 Coil

Nexus with dual 9'' coil

I do use a Fisher TW-5 on occasion

IDX Pro with 15'',old machine but really deep and also very cheap to buy for occasional use.

 

PI machines for extreme depth.

TDI Pro with 14x9 Coiltek,15x12 Commander Mono,18'' Detech Mono and 20'' Sierra Grande mono the big beast as i call it.

Crossbow PI with Garrett 14x10 Mono.

These coils cover most my needs,if you shop around you can get some amazing 'new' bargain,the 20'' Sierra Grande is normally a $500 just on its own,but after Jimmy Sierra problem with Whites the new coils had been sold off cheap,and including postage to the UK from across the pond it cost me just $190 for a coil of that size,it may sit around gathering dust for periods of time but not alot of money involved so this is why i have a fair few.

Regarding using large coils on detectors,before i invest in a new one i take into account the cost/use and reward ration on the initial invest in a coil,in the case of the 20'' coil above that more than ticked the boxes,so that is why i own it.Its great to speak to other detectorist that you have the largest coil going but unless its used and finds what you are looking for then it means nothing,just a bloody expensive lump of copper wire and plastic.

This is just my take on how i select adn use my coils for my hunting sites,we all of course use different setups.