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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.
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!
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
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
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
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?