Treasure Talk

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Which X-TERRA coil is best for me? - Part 3

April 13, 2012 04:10pm

Randy Horton
Randy Digger Horton

There are several things to be considered when choosing a coil for your X-TERRA. In Part 1, I mentioned that larger coils detect larger targets deeper, small coils are more sensitive to smaller targets, concentric coils provide a more accurate TID, and Double-D coils separate targets better than comparably sized concentric coils.

In Part 2, I explained how to check your soil conditions to determine if a Double-D coil might be beneficial.

One important piece of functionality we find unique to the X-TERRA is the ability to change the operating frequency of the detector by simply switching to a different frequency coil.

Just as when outlining the attributes of coil size and design, there are a couple generalities to be considered when considering coil frequency. Higher frequencies are designed to maximize their response to targets with lower conductivities, such as gold and iron. Lower frequencies are designed to maximize their response to targets with higher conductivity levels, such as silver and copper.

Don’t get the wrong impression that specific frequencies only detect certain targets. Each of the X-TERRA coils are capable of detecting anything metal. Some coils just do a more proficient job than others, at specific sites.

For example, higher frequency coils are considered the best coil for gold prospecting and jewellery hunting. This is because, on the X-TERRAs, high frequency coils expand the target ID range for low conductivity targets and compress that target ID range on targets with high conductivity levels.

Conversely, the low frequency coil expands the target ID range on high conductive targets and compresses that range on targets with low conductivity levels.

If you’ve read my eBook, Understanding your X-TERRA, you know that I prefer using the 3-kHz coil in and around old homesteads because it provides a very distinct audio response on deeply buried iron. If you've ever hunted an old homestead, you know how much iron can be buried in the ground!

With the high frequency coils, and to a certain degree the medium frequency coils, the audio response on deeply buried iron does not provide the harmonic audio distinction that I get with my 3-kHz coil. The response from this coil greatly reduces the “wrap around” effect often encountered when trying to separate deeply buried iron from an old coin.

This example not only takes into account the low frequency providing good information on high conductive targets, but also demonstrates how we can use this technology to assist us in identifying targets whose conductive properties are not “favored” by a certain frequency. This can best be depicted by comparing the width of each notch segment when using each of the three different coil frequencies.

3 coil frequencies

In Part 4, I’ll offer some practical advice for making a coil choice. And, finalize this discussion on X-TERRA coils.

Randy Horton (Digger)
You'll never know for sure... unless you dig it!


Thanks Randy. I just received my new X-TERRA 705 Gold, and have been wondering about a second coil for all around hunting, coins, treasures, beaches, kind of areas. Maybe I don't need a nother coil, sounds like the Double-D will do just fine.
Thanks again

Don S
Posted By: on April 19, 2012 11:05pm
Glad I could be of assistance, Don. As I've said, any of the X-TERRA coils will find all types of metals. Some just do it better than others. As I point out in my blogs, lower frequency coils are better suited for higher conductive targets, such as copper and silver coins. And higher frequency coils are better suited for lower conductive targets, such as gold. The elliptical coil that came with your Gold Pack will serve you well for much of the hunting you will do. However, in addition to the frqeuency differences, remember larger coils will detect deeper and smaller coils will separate targets better. What you could benefit from depends on the specific sites you hunt. If you decide you want to purchase another coil, you might consider getting a different frequency as there are definite differences in the manner they respond to various targets. But as I said, the elliptical coil that came with your Gold Pack is a great "all-around" coil. HH Randy
Posted By: Digger on April 23, 2012 01:18pm
The comment section regarding your E-book was closed but I wanted MY chance to say thank you for the attention and hard work that you surely, put into it and articles such as the above. The availability of your E-book was one of the deciding factors in which detector I would purchase as my first.I now own the X-TERRA 705 Gold and love it! I am still in the early stages of learning but am hanging on every bit of advice that you publish. I have printed out and read your entire e-book for the FIRST time and will reference it often in addition to my manual. Don't wear yourself out but, keep it coming as you can? Now, I'm heading back to this sites search engine to see what other pearls of wisdom and/or experience that I can learn from! Thanks again! ;D
Posted By: HotDiggity on April 30, 2012 12:35pm
Thanks for the kind words D. I always appreciate hearing from those who benefit from my efforts. Although the ebook should give you a headstart on becoming proficient with your X-TERRA, hands-on experience in the field will be your best learning tool. Thanks again for taking the time to comment. HH Randy
Posted By: Digger on April 30, 2012 12:59pm
Digger I have set up a sort of test field in my back yard and find it very useful in determining how my X-TERRA 705 works. I am just about ready to try to detect in a school yard and State park. I was thinking about doing some testing there also such as going over the area first with my 6" Double-D, mark my signals, and without digging change coils to my 9" Concentric and mark again. After digging I should be able to see if one of my coils has missed different targets. I have studied your instructions on setting up the 9" coil,AND FIND COINS AS DEEP AS 9",I would ask if I use the same settings for the 6" coil, maybe with minor changes. Do you have a suggestion for me. Thanks I take your writings as encourgement because I was getting discourged before. Where do you suggest I study setting up for prospecting mode as I have devoted most of my time on treasure hunting with my X-TERRA 705. STUBFINGERS
Posted By: stubfingers on May 21, 2012 07:22am
Thanks for the questions. If you are using Automatic GB or Tracking, chances are you won't see a lot of difference in setting up your detector with the 6-inch DD at 18.75 kHz. However, the design characteristics of the DD coil allow it to compensate for the mineralization better than your stock concentric. Add to that the smaller diameter and less soil being analyzed at any one time, and your ground phase reading should be markedly lower. This should result in quieter operation with less falsing. But again, if you are using Auto GB or Tracking, don't worry about making adjustments. They are taken care of by the electronics in the X-TERRA. A suggestion for going back over the same turf with the 6-inch as the 9-inch is to make sure you overlap your swaths with each. Sometimes when using the smaller coils, it is easy to get in a hurry and not overlap the swaths. Another suggestion would be to work the area at a 90 degree angle to the initial direction. Coins that are on edge will certainly provide better target signals from one direction than another.

If you are hunting an area that is highly mineralized, detecting with a small DD coil in Prospecting mode will greatly improve the detector's performance. As to Prospecting Mode "tips", when using Prospecting Mode, know that targets will be identified by audio response only. Prospecting Mode does not provide target ID on the display. Also recognize that the numbers on the screen represent the level of Iron Mask discrimination, not characteristics of specific targets. If you do a google search for X-TERRA Prospecting Mode, you should find several good videos from folks demonstrating their techniques. Among the best is a video provided by Des Dunne of Minelab. Although it was originally developed for the X-TERRA 70, the same prinicipals apply to the X-TERRA 705. If you've not found the Findmall X-TERRA forum, I encourage you to take a look at it. There are a lot of very knowledgeable folks there who are always willing to help fellow detectorists. And If you have any specific questions regarding the X-TERRA for it's functionality, please don't hesitate to ask! Thanks again for responding to my TreasureTalk blog. HH Randy
Posted By: Digger on May 21, 2012 12:05pm
Hi Randy, really enjoyed this mini-series I hope we will soon get Part 4.
Is there any benefit running in prospecting mode on beaches with a 10.5" DD or is the beach mode the better alternative, given your comments about the 6" DD coil
Thanks D
Posted By: DDazzzle on June 05, 2012 01:36am
Thanks for the comments and your question. Unless you are intent on digging every target at the beach, I'd opt for using the Coin / Treasure - Beach Mode, opposed to Prospecting. Although Prospecting might provide a bit more depth, it has limited discrimination (only iron mask) and doesn't provide target identification. The Beach Mode not only provides a full range of discrimination options, but it provides both ferrous and non-ferrous Target ID. In addition, by activating Ground Balance Beach, the X-TERRA's ground balance system sets the proper ground phase for any combination of magnetic mineralization, as well as the conductive mineralization typically found in salt - sand environments. One additional tip.....if you implement Ground Balance Tracking in Beach, ferrous targets and some very low non-ferrous targets may be "balanced" out. For this reason, I'd recommend that you not use Beach Tracking in areas where targets are close together. HH Randy
Posted By: Digger on June 05, 2012 01:05pm
Hi Digger,
Im a few months into metal detecting and starting to get the hang of my Minelab X-TERRA 705. It came fitted with a DD 9inch 7.5 and I search mainly large ploughed fields in England at rallies, often sites that have previously been searched. I find the X-TERRA really good for large deep stuff. However, I am sure I am missing the smaller thin silver hammered coins which club colleagues pull out at a rate of probably 3-6 on a typical dig and the half grats are tiny often elizabethan or even earlier. Whereas I tend to find the odd large penny, crotal bells and every horseshoe in the field (I get mixed signals for horseshoes). I note all the stuff I find is large and deep.
As I would like to find the small hammered silver coins should I be thinking of a different coil with higher frequency and what do recommend. Or have I bought the wrong machine for my needs?
Appreciate advice
Posted By: fenlandspaniel on September 02, 2012 05:29pm
I've used about everything out there and find the X-TERRA to be an excellent choice for hunting in areas where the soil has been broken. If I am hunting a plowed field, you can almost bet I'll be swinging my X-TERRA 705. Considering the small size of the hammered coins you seek, I'd opt for either the 6-inch DD at 18.75 kHz or the elliptical DD at 18.75 kHz. The higher frequency DD coils will be more sensitive to smaller targets. And the DD design will help neutralize the effects of the mineralization you have there. The "solid bottom" will allow either coil to be worked without getting hung up in the stubble. Admittedly, the elliptical coil will cover more ground with each swath. But don't underestimate the depth of detection of the smaller 6-inch. In the fields I hunt, the 6-inch coil has been "more productive" than the elliptical. Very easy to navigate up, down and in between the furrows. HH Randy
Posted By: Digger on September 10, 2012 01:42pm
Evening. I am not really new to detecting, I have had Whites and Bounty Hunters since the early 1980's but have not really gotten out that much. I now have a X-TERRA 705 Gold Pack and since I retired, I'm getting out much more. In this area about the only real place to detect is Sand and Gavel mines, in the glacial drift. I am trying to learn the new detector but my 68 years are working against me. After 23 years as a aircraft mech then a missile electronics tech and 3 College Degrees, you would thing this would be easy but I will keep plugging away at it.Your book and articles do help immensely ! Thank you for all of your assistance and I look forward to reading more of your advice.
Posted By: bill7929 on September 15, 2012 01:13pm
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