A DD coil vs a Mono

Afternoon all. This is my first post on this forum, I had a few posts on the previous, now defunct one. I think this gold site forum has come a long way in the short time it has been around. I have enjoyed reading it & have learnt a lot, thanks to all. I know there have been heaps of comparisons & threads on Monocoils vs DD. I own a GP3500, with only its original 11" DD coil. I am seriously thinking of updating to one of Coiltecks new coils 14". The following statement might sound simple" if a DD coil can be switched to mono, then why bother buying a mono in the first place! With the DD coil you virtually have 2 coils in one. Now I am presuming that the DD coil switched to mono, would have the same capabilities as a mono in that same size.Eg 14" DD or 14" mono. Could some one enlighten me ? Davo

Davo, if you do a search of this forum there have been a few threads on the differences between pseudo monoloop mode with a DD and a true monoloop. Essentially it is due to winding size (a 14" Mono is a true full size winding compared to a 14" DD which is only half that size) but also the way pseudo mono mode works. Traditionally a Monoloop coil transmits across the whole winding then receives across the whole winding through switching, whereas a DD coil transmits on one winding and receives on the other, generating its signal response across the centre of the coil in a blade pattern. When in pseudo mono mode a DD coil transmits on one winding but receives across the whole coil but because of the second winding generates its response off the left winding (in the centre as per a normal DD response and then the left hand edge as per a Monoloop would on its whole edge).

A more traditional Monoloop coil will have far more depth than a pseudo mono coil due to the second winding nulling the coil (desensitizes), so generally speaking it is best to stick to shallow areas with numerous nuggets near the surface where a traditional DD would struggle due to lack of sensitivity but a monoloop would also struggle due to excessive ground noise and hot rocks.

For very good performance with a DD coil in high mineralisation but where the nugget trend to be on the smaller size try using the GP 3500 in DD mode, Deep audio, Sensitive timings, Auto tracking in the Medium tracking speed.

Hope this helps, for more info we have two videos on the GP series machines that go into great detail on the various functions in gold fields conditions www.aurumasutralis.com

JP

Hi Jonathan, I still find it very technical but do get the gist of it. I definately will be buying the mono coil as it must have more punch in relatively quiet ground. Ps I do have your video " The Outback Prospector" I can't remember if you claryfied my statement in your video. Must see it again real soon, Thanks kindly for you Pro- Help, cheers Davo

G'day again Davo and thanks for your support of our videos. The best way to describe the differences between a Mono and pseudo mono is to liken it to a computer, the Mono only coil is hardware based whereas the pseudo mono mode is hardware and software based (hardware being the need for a DD coil and software being the electronic trickery behind it to achieve the pseudo/mono result). In this instance because of the second winding of the DD coil maximum depth is not achievable compared to a monoloop of the same sized winding, but the tradeoff is the pseudo mono mode (software/hardware based method) will be quieter due to its DD type characteristics in high mineralisation (not as quiet as a DD but definitely quieter than a true hardware based monoloop)

Hope this helps,

JP

Gday Davo

The standard 11" gp series coil that comes with the gp3500 is an excellent coil, and deadly in the pheudo mono mode on small shallow bits, another advantage of using it is that the descrimination function will still work.

Another excellent coil on the 3500 is the coiltek 11" mono, you will get better depth with it but it can be a little noisier and the descrimination feature wont work with it so it may take some getting used to, if you are looking at getting a 14" coiltek dd coil then the later cream coloured dd pro one works quite well with it, if you are considering a larger mono coil then the nuggetfinder 16" super light mono works well on the 3500 and it really is super light weight so you can swing it all day, and you will also get the small pieces with it as well.

There have been some changes to the nuggetfinder coils, and they are now selling the advantage range of coils, they may perform a bit differently than the earlier model light grey one, they are now a darker grey colour plastic, so it may pay to check with other users before buying one.

cheers

stayyerAU



































,

G'day Davo,
There's another reason why I use a true mono as opposed to a DD in mono mode...weight....a mono the same weight as a DD equates to a much larger coil i.e. much more depth, and coverage.

I love my 14x9 Goldstalker for this very reason....it's so light (575 grams) many grams lighter than the stock 11" DD. I can swing it all day without a bungee, and even swing from the bottom of a creek bed right up the bank side above my head without aches and pains in my shoulder or arm.

Also when I go over patches again with the 18x12 Goldstalker I don't find much at all that's been missed by the 14x9, it's a little ripper, but it's actually only equivalent in winding size to an 11" round mono. For comparison though, the magnetic field developed from this coil would be roughly equivalent to the transmit winding on a 16" DD which would be half the weight again.

Incidentally Eric Foster one of the most knowledgeable Engineers in detection technology says that the 11 inch mono (some 600 square cms) is the best coil compromise over all, when seeking small to medium sized targets in difficult ground.

Detection depth is constrained by target size, soil mineralisation, magnetic field strength which is also constrained by power available to a handheld device and maximum allowable EMC levels, present electronics and physical laws….when all this is taken into account the old 11” mono is bang in the middle of averages.

Cheers
Grey

Hi again, Thanks to Jp,alchemist& stayyerAu for your useful replies. Have another question especially for stayyerAu. You are suggesting I go for the nugget finder 16". I owned a NF 20" 2 years back & found it reasonably light, but really had problems pinpointing a target. Obviously I was trying to find something large, but each time I thought I had a target, there was no way I could pinpoint what ever was down there. I had dug 30-40cm sometimes, but frustrated I gave up believing it was ground noise? Did you have any problems pinpointing a target with the NF16", & finally where abouts on the coil do you believe to be the most sensitive. Cheers Davo

Gday Davo

The reason I suggested the NF 16" mono is because I have used one on my 3500 and found it to be stable and even though its a largish coil you will still get good ground coverage and the little bits as well, they also do it in a 14" that should be similar in performance to the 16", but again it will be lighter than the coiltek 14" dd or mono coil.

Pinpointing is always an issue with large coils whether they be dd or mono, if you were using a large mono coil previously then you would have experienced some issues with it picking up ground noise as well, some deep targets will also sound like ground noise, so you have to just dig until you find out what the noise is, also with some experience you will soon be able to tell the difference in most cases.

The mono coils are sensitive all around the edge of the coil, but the most concentrated part is the centre, if you imagine that the coil is putting an inverted cone shaped signal into the ground, the centre point is the sweet spot so to speak, so you have to centre the target by passing the coil over it until you get the best signal response, either mark the ground with your foot or keep an eye on the spot, then turn 90 degrees to it and wave the coil over the ground again, doing the same thing, the intersecting marks will give you the position of the target.

The deeper the target the broader the response, if the target is reasonably shallow (or large) then the signal could be more defined, take care to start to scrape away the overburden well away from the signal centre, and then start to dig away well to the sides of the target, as you might end up damaging a good nugget with the pick, get the area nice and even, so you can wave the coil over the surface without any obstacles.

When you are fairly confident that you are close to the target, and providing you have created a large enough hole, you can turn the mono coil on its side and use the edge to pinpoint the target to some degree,( if you can not hear the target when you do this then its deeper down) if this becomes too difficult then put a small coil on, I have an 8" minelab mono for this (coiltek have just brought out a 6" mono) which would be good , or invest in a pinpoint probe, also a coiltek product.

This is the method I use, others may do it differently to me but it achieves the same end, sometimes if I have an iffy signal I just mark it and later in the day when I have had enough of the bigger coils I will go back with a smaller coil on and check it out again, sometimes when patch hunting I will also carry a small mono coil with me as well just in case, saves a trip back to camp.

Hope this info is some use to you.

cheers

stayyerAU

Good advise from stayyer on the use of a mono coil.
Please understand that using a mono coil will have you investigating more noises and broad signal responses than a DD, there will be a lot more hot rocks and mineralisation false signals that will have you digging. With practice you will get your own mental discriminator well tuned. Fatigue is your worst enemy with a mono on any machine before the 4000. There is only so many investigation digs a person can do in one day before you start walking away from signals. I would recommend to anyone new to this game that a DD is the coil to learn with and then move across to the mono for more thorough investigation of the ground you are detecting. Do the change to early and you will overload the whole experience.
Brett.

Stayyerau [SLR man myself] Echidna digger you raise some interesting points.
Look it seems to me a new chum should learn his trade with the dd. . . . At least
up to the 3500. Less confusion more positive input through the headphones.
Question which coil produces best results across the board? Ill bet you it’s the standard 11 inch coil supplied.
Here’s a tip for newbie’s .run your 11 inch coil on the ground and I mean on the ground.
Skid plates are cheap. I wear out one about every 14 detecting days.
Kick and scrape anything that causes your eyes to blink on the threshold.
When you feel confident move up to the monos to recheck the ground...
Regards Adrian

Adrian,
I believe you are right, the 11" DD is probably the sweetest coil for the rewards that it gives. 14" elliptical DD are very similar only more sensitive on small shallow ones. The 11" round may give a bit more depth. Either way they are sniper rifles as far as I can tell.
My opinion is: A new bloke should resist the need for big coils until he understands the small ones. Lets face it, if you have a huge coil you will miss the small ones that are prolific in comparison to the big ones and with a big coil in inexperienced hands a big deep target wont be noticed anyway.
Ive truncated the whole story but that's how I see it.
Brett.

Sorry Guys for the delay of my response! Sounds like you guys know what your talking about, I will resist in buying a too large coil. I'm thinking the NF 14" mono will be my next coil up from the original 11" DD. It seems to be light & powerful enough to do most jobs, especially combined with my GP3500. I'm reading between the lines that you think I'm a " newbie". I might surprise some of you, as I bought my first detector back in 1984.Minelab 15000 I think it was. I was working for Mt Newman mining at Port Headland, WA ( Pilbara region). As I worked 6 days per week, I realisticly was out of reach of the Goldfields for a day trip. One weekend I manage to have a few days off, so headed to Nullagine ( using David De Havilands " Gold& Ghost" great book for referance ) I drove through "Marble Bar" which looked promising back then, however restricted for time I kept driving. At Nullagine there was just a pub, ( only evidence of civilisation ) not far past it I drove in my old subaru parallel to a dry creek several ks north. Every several 100 metres you would see signs of private, small habitats & workings. To cut a longer story short, that early model detector went over heaps of gullies, hills & flat country side for a day & a half. Unfortunately my detector didn't come up with the goods. The area was extremly high in mineralisation & it had no hope in penetrating the ironstone. If only I had the GP with me back then 25 years ago. ( my mind boggles) Anyhow back to the present, just like to thank all the guys on this thread for devulging there experienced tips for me, keep it going, it's the best Gold Forum around! Cheers Davo