Which Coils For Which Situations

[oldmancoyote1]

I bought somebody's GPX 4500.  It came with 4 coils.  Then I realized that I don't have a clue what are the strengths and weakness of the different coil configurations.  What are some general principals to guide folks in matching coils to the situations that they encounter?  I don't recall having seen any guidance on this.

Thanks

[phrunt]

What coils did you get with it? 

Congratulations on getting a 4500 by the way, nice detector.

[1515Art]

I general you find mono coils and double d coils there are different windings sometimes spiral windings for one and different shapes and sizes and to add to that coils made by different manufactures. In simple terms mono coils tend to be more sensitive and dd run smother under certain conditions. Match the coil to the terrain aiming to keep the coil close to the ground, rocky areas favor smaller coils and wide open spaces larger coils, larger coils can give more depth and ground coverage trashy target infested ground I prefer a smaller coil to better separate target signals. Start with a coil that fits the terrain and get to know all your coils you’ll likely find a favorite in a smaller to mid size coils Phrunt is right to ask what coils you have there are a few really good popular ones if you have one usually an elliptical it will become a favorite you will tend to use most of the time decent depth and coverage good sensitivity and easy to shove under brush where nuggets hide.  Phrunt has every coil ever made ( I’m exaggerating) he knows them all well but post up what you have, include pictures and he’ll know but most important try them all the most important thing is knowing your equipment. After that… buy more coils, lol. Good luck out there and be safe.

[Steve Herschbach]

Use a mono when you can, and a DD when you have to (due to hot rocks and mineralization). Keep in mind that what matters as far as depth is the size of the receive coil. With a mono that is roughly the size of the coil itself. With a DD it’s maybe 60% of the coil area or less. So a if a mono coil and a DD coil are the same size physically, electronically the DD is the smaller coil. The DD handles the ground not only by separating the transmit and receive coils, which are the same winding in a mono, but by also “seeing” less ground. The DD is less prance to EMI for the same reason - smaller receive coil. Which goes back to use a mono if the ground/hot rocks and EMI allows, as you are getting more bang for the weight.

DD coils were more popular prior to the GPX series, but the GPX was designed to take advantage of the inherent pluses in running a mono coil, and mono coils dominated from the GPX 4000 and after. But for the worst of worst ground a DD still has it’s place.

[oldmancoyote1]

Thanks for the info so far.  I have these coils:

14x9 Double D Evolution Nugget Finder

11” Minelab Mono Commander

11” Minelab GP Series

8x6 Sadie Advantage LITZ Wire  Nugget 

When I first bought these coils, I asked Ray Mills which he would recommend for someone new to PI machines.  He recommended the Sadie.  Now that I am a  little more comfortable with a PI, I want to know how I ought to adjust my choice of coil according to the conditions.

Thanks

[phrunt]

So, I'm guessing your GP Series is a DD 11", and you've got the Mono Commander also, the Sadie being a mono and the 14x9" EVO which I am sure should be a Mono not a DD, what makes you think that one is a DD? 

If the EVO is in fact a Mono I'd be using that over the Sadie, more sensitive to small gold, and only use the Sadie if edge sensitivity or getting into tight spaces is required.   The Sadie is bundle wound, the EVO will be flat (Spiral) wound so it's edges aren't as hot but the middle of the coil is a killer on small gold.

That 11" GP Series if it is the DD would be your choice for high EMI areas.

 

[oldmancoyote1]

10 minutes ago, phrunt said:

So, I'm guessing your GP Series is a DD 11", and you've got the Mono Commander also, the Sadie being a mono and the 14x9" EVO which I am sure should be a Mono not a DD, what makes you think that one is a DD? 

If the EVO is in fact a Mono I'd be using that over the Sadie, more sensitive to small gold, and only use the Sadie if edge sensitivity or getting into tight spaces is required.   The Sadi

I'm down in Mexico for the Winter so I can't answer your question.  I think I just screwed up because in my lack of experience I thought the elliptical shape meant it was a DD.

[phrunt]

2 minutes ago, oldmancoyote1 said:

I'm down in Mexico for the Winter so I can't answer your question.  I think I just screwed up because in my lack of experience I thought the elliptical shape meant it was a DD.

The good news is it's a mono, and one of the best coils available for the GPX in my opinion.

[RickUK]

I am aware that this is oldish thread,but it is very relevant to me at the moment,i have a selection of GPX mono coils that i use/d with my TDI Pro.But since i have just recently got my GPX4500 i started buying DD coils to take advantage of the iron rejection.

This has had me thinking am i buying the right coils ie DD for my type of detecting here in the UK which is predominately hoard/artefact hunting,currently have my GPX setup with a 11'' DD AI coil but after reading this road i am having my doubts ??our ground here in the UK is very mild infact very very mild compared with say some areas across the pond and in Aussie land.

As i will be mainly using the GPX on cleanish ground conditions i am having 2nd thoughts about going totally down the DD route,these are these smaller sub 15'' coils that i have the option of using for hoard hunting.

Stock ML 11'' Mono

6'' Coiltek Mono

Coiltek 14x9 Mono

Detech 11'' DD AI coil

ML 15X12 Mono

ML 15X12 DD

Detech 18'' Mono

I dont really want to use the large coils unless i really have too,so was wondering is the Coiltek 14x9 a candidate for a everyday use coil for pasture or deep ploughed or just use the stock 11'' Mono,this thing about not really being able to use the iron rejection is really niggling me,or should i just keep using one of my VLF machines till the time to say locate the hoard and then change over to the GPX with a Mono coil.

Any input would be most welcome as i am going around in circles changing coils over thinking that i have the right coil combination for the GPX.

[Redz]

I presume you are using the 4500 PI because you want depth. Otherwise you would use VLF with target ID. If you want depth then the larger monos are your coils. Iron discrim doesnt work very well at depth anyway.