Interview Metal Detector Aftermarket Coil Leader Coiltek

Coiltek is a recognized name in the metal detecting community for making aftermarket coils for metal detectors. The company, which was established in 1996 out of Australia, is well respected by detectorists, serious prospectors, and large mining companies around the world.

Coiltek Coils Minelab

Trevor Ferraresso, who holds the title of Sales & Technical Director, and has worked at Coiltek since 1999, answers my and readers’ questions below. Prior to working with Coiltek, Trevor worked for Minelab. 

See the interview questions and his answers below.

History of Coiltek

How and why did Coiltek start? Who founded it, and what was their background in metal detecting or prospecting?

This goes back to the very start of Minelab really (the early 1990s). Minelab was just a bunch of smart individuals, Bruce Candy was the brains behind the technology, and they had the ideas and ability to put together the first detectors from this start-up *innovative company. They were making their own coils to suit the detector, and these were produced by John Kah, who was part of the early production team. From my understanding, John then started to see the potential of demand in 1996 and moved out from his home shed where he was building the coils to the factory that we are still in today in Salisbury South, South Australia. This is when he created the company Coiltek Pty Ltd and ran it with his wife and a small team of skilled individuals who were making the coils under the Minelab brand. John was never really ‘into’ metal detecting itself but was very clever with manufacturing and became very familiar with how and why the coils work and refined this to ensure a high-performing, high-quality coil. I started with Coiltek in 1999 and worked closely with John and ended up managing the company in 2005. John moved on from the company in 2007, which is when my wife and I bought the business and continued to innovate and create the Coiltek coils of today.

Coiltek Goldhawk

Metal Detector Coil Technology

Please explain to our readers the technology behind a round DD coil and a DD oval coil. When would one be better than the other?

DD coils are the most common coil type in the market today, especially on the coin and treasure detectors. The main difference between round and elliptical is the width of the coil’s transmit and receive windings. The wider the windings are, the better the magnetic field produced and received is punching deeper in the ground. As we squash the windings to become more elliptical, we are essentially reducing the detection depth to a degree. There are other factors that contribute to this like target size, orientation, and soil types, but the narrower the coil (of any configuration) the shallower it detects. However, there is an added bonus to the elliptical shape… you will increase your sensitivity to the smaller, shallower targets, and pinpointing them can be easier. The elliptical shapes are also better at separating targets – when trash and treasure are lying close together in the ground, the smaller elliptical coils can decipher between them easier. For the more open ground where targets may be deeper than the top 8-10 inches the round coils are very well suited and have a good coverage and performance ability. If the terrain becomes more rocky or overgrown, where a larger coil is harder to swing, then the elliptical coils are great to maneuver around and have a sharp target response. Ultimately, it’s always good to have a few coils in your kit as not one coil size and type will get all the targets – this has been proven time and time again by many detector operators when they go back to a successful area with another coil size. 95% of the time they will get more treasure.

For those detectorists who don’t know, please explain when it is wiser to have a solid coil disk versus an open coil.

Sometimes it’s not always an option to choose between these designs as the coils that are made today tend to mostly be open web for treasure hunters. The main reason is for weight reduction, which is a big factor for the modern detector operator. In years gone by, we had an open web range and solid coil range for the GPX5000 Gold machines and some loved the solid coil design, especially when there was grass and light vegetation growing. The solid coil was able to push to the ground easier and get through this terrain easier. The open coils would get caught up in the undergrowth and fallen sticks etc and hinder the swing. If there is an option for your detector, then decide what is best for your hunt when you look at the terrain. Open coils are lighter weight and good for most detecting environments but may need more controlled swings when in difficult terrain. Solid coils are great for open areas and can push through vegetation easier without getting caught up.

Some of the newer detectorists might not understand what DD coils are, what the two DD’s stand for, and what is a concentric coil, also known as a monoloop coil, can you go into detail and explain?

Now this is the bit I like talking about being more technical and I love understanding why the coils work. The three most common types of coil configurations for the coil windings are DD, MONOLOOP, and CONCENTRIC. A coil has multiple laps of copper wire inside and the wire type required differs between the detector technology and models that are in the market. 

A DD coil essentially has two different windings in the coil. One is a transmit winding which sends the magnetic field signal into the ground and the other is the receiver winding, which then picks up any metallic objects’ field responses as they return to the surface/coil. These coils are good for discriminating between targets and work best in highly mineralized soil types as they balance out any interference from this soil type.

A MONOLOOP (MONO) coil type only has one winding in the coil, and it transmits and receives from the same winding. These are only used on the pulse induction type detectors, like GPX and SDC from Minelab. I do not know of any MONO coils working on treasure detectors. The detector and coil need to transmit a signal, turn it off, then listen for a signal response and convert to audio if received, and then repeat the process many times per second to be a successful coil for depth, sensitivity and balance on the ground conditions. The MONO coils will generally go deeper and have better sensitivity than a DD coil of equivalent size when used on the pulse induction detectors. These are the main go to coil types for the GPX6000 users today.

A CONCENTRIC coil is essentially a DD coil, but the windings are circular and like a donut in the coil, with the transmit being the outer ring and the receiver being the inner ring of windings. The receiver coil needs to be tuned to the transmit so that the windings do not interfere with each other when the detector is pulsing its signals for detection. I have not had a lot of experience in making this type of coil as we find the DD and MONO coils are better suited to the majority of soil conditions and detectorists with the modern detectors.

Goldhawk Series
Available in 3 sizes, Fits Minelab GPX 6000, Waterproof 1m / 3ft. Two-Year Warranty

Is there a reason why most manufacturers are using the DD coil configuration these days? The reason for the last question is, if you look back at older designs, coil structure was all over the place culminating in the bigfoot coil; then all of a sudden, everyone moved to DD and has sat there without much design change for the last couple of years, but now some manufactures are venturing back to concentric coils.

DD coils, from my understanding, perform better in the majority of ground types experienced around the world and I believe this is the main reason for them being so popular with manufacturers. The Concentric coil types tend to struggle with the mineralized ground and are more temperamental than the DD. The DD coil configuration is definitely better for this purpose and the main reason for the concentric types to not be the coil choice for the major manufacturers. You will find concentric coils available for some types of detectors, but for me, I would always prefer a DD and MONO over a concentric until there may be a new innovation to change that in detector performance.

Coiltek Technology & Build Quality

Regarding basic coil layout, how different does CoilTek make their coils when compared with the coils from the manufacturer? 

We definitely have our own technique when it comes to coil manufacture and we take pride in that ability and keep as many techniques a secret from our competitors. Having said that most manufacturers of coils, whether OEM or Aftermarket, will need to ensure their coil follows the technical specifications required by the detector. You cannot push these parameters too far out of the tolerance required before the coil starts to behave poorly and customers get frustrated with extra noise or low sensitivity. They are quite an art to get right time and time again, which is why we have strict policies and procedures which need to be followed to ensure a great performing coil. As all manufacturers know, you don’t get it right every time as the coils are mostly hand built, which can sometimes bring in small issues, but it’s our quality checks that ensure we keep the coils performing well. Some of our coils are tested at four different stages during the build to eliminate the most obvious or even subtle issues. It’s the small differences in our manufacturing techniques and the fact we are always innovating and reviewing our processes to keep in front of the game. We also encourage and appreciate real feedback from our customers, as they are the ones who truly know how the coils are performing. Any feedback is gathered and communicated to our technical team to review and make changes if approved.

Are the coils built in Australia or are they built in another country?

We build all of our coils within Australia, in our factory in Salisbury South, South Australia. We do get around 25% of raw materials from international suppliers as it’s difficult to find certain things within Australia, but we do our very best to use local suppliers and support the Australian Market. We have a team of dedicated people who love building the coils and hearing the success stories of gold and treasure being found with Coiltek Coils. We have no intention or desire to send manufacturing offshore.

Coiltek Nox Series
Available in 3 sizes. Fits Minelab Equinox 600, 700, 800, 900 & Xterra Pro. Two-Year Warranty.

Coiltek Warranty

Can we talk about your warranty? For example, if you own a CoilTek coil and your coil’s ears break, is it covered under warranty?

We have a 2-year manufacturer’s warranty so any manufacturing defects or issues from the purchase date are covered for 2 years. We take great pride in our service and warranty ability and always do our best to help the customer with issues as quickly as possible. For the instance of the coil wings/ears, we review if the coil ears have had a manufacturing fault or if they have had excess pressure in a sideways motion to make them crack. In the rare case, a user has either fallen or used the detector as a way to stand back up after getting their target, and the shaft is moved too far out of straight to make the wings flex too far and then break. This is something to always be aware of and take care of your coil as this will ensure you have great detecting experiences each time.

Do you feel coil stiffeners help or hinder a coil, making the coil ears break more easily, or do you recommend being proactive and using a coil stiffener not to have ear coils break?

I have not had any experience or investigation for coil stiffeners. We build our coil wings very strong and have not had any major issues with them breaking. For the Coiltek coils, I would say that people do not need to use them, but it is a personal choice if they do.

When sending in a Coiltek for warranty, what is the average turnaround time for getting the coil back?

Coiltek metal detector

This does depend on where the customer is located and our stock situation. We keep a small amount of coils for warranty change outs, but there may be instances where we are out of stock and we then move production of the coil through fast. Most of the time, we endeavor to rectify any warranty claims within 10-14 days. My team is instructed to communicate within 48 hrs of receiving a claim and keep communication up as best as possible during the time until it is replaced. If our dealer network in the region required has stock of a coil, we can also request for them to help the customer by swapping it out in store or mailing and then get the bad coil to us for review. This can speed up the process in some instances. We also try to get as many coils back for review as possible, as we can learn from these failures and see why it failed and put actions in place to rectify during production if deemed necessary. Any failure is a lesson learned for us and our team is very solution orientated to keep improving the performance and reliability of the coils.

I see that warranty is transferable. How does someone who bought the Coiltek second-hand transfer the warranty?

Yes, correct, if the coil is sold during its first two years to another detector operator, the warranty will continue until two years from the date of the original purchase. I recommend the new owner to contact us to say they have taken possession of a coil they believe to still be in warranty. We can then do checks on the type and serial number to confirm this and if they have an issue, they must contact us to inform us so we can assist.

Counterfeit Coiltek Coils

What are some signs your Coiltek coil could be a counterfeit? 

This was a big problem for most manufacturers around 10-12 years ago. The market was so crazy for detectors and coils going into the African region – I have never seen anything like it and we most probably won’t again to that scale. As demand outweighed supply, it allowed the counterfeiters to swoop in and copy detectors and coils making poor quality products and satisfying their ‘make a quick buck off unsuspecting customers’ egos. It still frustrates me to a degree today to think that people can feel good about what they are doing when counterfeiting. If someone is ever unsure if their product is counterfeit or original, please send us several images of the coil, the wings, labels and plug so we can review this closely and keep in touch with the person to assist. Counterfeiting is nowhere near as prevalent as it was and most of the counterfeit products are no longer in the market but It’s always good to triple-check. Sometimes if a deal for a detector or coil is stupidly good it may be because it’s not original, so buyer beware at every purchase and make sure you are buying through a registered dealer which can be found on our website.

Where has Coiltek seen counterfeit Coiltek coils pop up for sale online and geographically?

Mostly online through marketplace selling hubs, but these are more aware of manufacturer’s rights and do take steps to remove any suspect listings. It is up to the manufacturer and customer to ensure the listing is genuine. People living in the Middle East and Africa have been the most targeted as the markets were not as established back 10 years ago so people did not have the awareness of genuine and fake. As these markets matured, we have seen greater awareness from the people as well as many companies as well as Coiltek have taken steps to provide education and awareness to the consumer on how to watch out for counterfeits and ask the manufacturer for confirmation. Again, the best thing the consumer can do is buy from Authorized dealers or direct through manufacturer’s websites to ensure genuine products are purchased.

Future Coiltek Coils

Minelab Manticore users are wondering when you will release coils for the Manticore.

This is definitely a question we are being asked a lot and we can’t say too much on this topic at the moment. We have an excellent collaborative relationship with Minelab so all I can say is that we have had talks about Coiltek Manticore coils, but as far as when and what, people will need to wait for more info if it comes. Best to subscribe to our newsletter via our website as we do let those on the list know before the rest of the world.

Will you be making coils for The Legend from Nokta?

There are always possibilities for Coiltek coils to be made for other manufacturers, and Nokta makes a great product that many people like to use. Having more coils for this brand would definitely assist the user with increased options when detecting. Again, you never know what may come in the future.

Do you have any other future developments that you think our readers would like to know about?

We have some exciting news to come out in the later half of 2023, which will certainly be a great option for the serious detector operator. Again, join our mailing list and watch our socials for the latest news and release information. We may have some sneaky leaks of info in the next few months.

I would like to thank Trevor Ferraresso from Coiltek for answering the above questions.
Please remember, if you are interested in purchasing a Coiltek coil, contact a certified dealer and ensure they have an International Coiltek Dealer Certificate. To learn more about Coiltek, please visit their website at or their social media channels Facebook (, Instagram (, YouTube (

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