steve herschbach
New member
I have been laying fairly low with the Nokta Impact so far. Part of that is I have been busy on other things. The main reason however is I quickly zeroed in on how I think the Impact will best serve me as a detectorist.
In general I think I can speak for most people when I say we all like lighter weight detectors. However, one area where lighter is not better is when you use large coils. Balance is every bit as important as weight as it determines the amount of torque applied to your wrist as you swing the detector. A large coil on a very light detector creates a very nose heavy detector, one that will put more strain on you when you detect than a heavier but better balanced detector. It just so happens that the Impact with the rear mounted battery power/speaker module is a good design for a large coil from an ergonomics standpoint. This is especially true when in my experience Nokta has designed large coils that are quite light for their size. I was probably one of the first people that really zeroed in on the new IM40 15" x 14" DD coil when it was proposed for the Impact by Nokta. I got on an early wait list for the coil, and just received mine.
The IM40 DD coil measures 15.5" x 13.75" and comes with a fitted skid plate/scuff cover. The coil weighs 1 lb 13.0 oz or 822 grams as pictured with skid plate and cable and weighed on my postal scales. Yes, I had to say that as some people exclude cable weights from coils! For comparison the stock 11" x 7" IMP29 coil weighs 15.7 oz or 446 grams. I like the flat blunted ends on the IM40, which does help the Impact stay upright as the trailing edge of the coil acts as a flat bearing surface when the detector is at rest on the ground.
I am not usually a fan of larger coils and in fact tend to lean to smaller coils for a lot of my urban metal detecting. Large coils "see" more area which can work against them in highly mineralized ground or in areas with lots of closely spaced trash. However, large coils even if they do not get more depth in highly mineralized ground can cover more area faster, and often ground coverage is every bit as important if not more so than depth. In medium to lower mineral ground a large coil can also offer that magic thing all detectorists crave - more depth!
The Nokta Impact has another trick up its sleeve that favors large coils; the ability to change operating frequency on the fly. High frequencies offer more sensitivity to small items and quicker separation in dense trash as well as extended battery operating time. The main issue with higher frequencies is they also "light up" highly mineralized ground and hot rocks more so than lower frequencies. This can work against machines that are locked into higher frequencies when attempting to employ large coils in highly mineralized ground. Lower frequencies give up some of the high frequency "hots" on small targets but also are less sensitive to ground issues, including salt mineralization. The ability of the Nokta Impact to run at 20 kHz, 14 kHz, or even 5 kHz makes it very well suited for running very large coils. This is accentuated by the plethora of all metal modes available on the Nokta Impact which can deliver extreme performance when coupled with a large coil.
The bottom line is I think the Nokta Impact and IM40 coil may be one of the very best options available for a person wanting to run a large coil on a VLF detector, with depths in all metal modes and milder ground that will challenge many PI detectors.
For a lot of what I personally do, like gold prospecting or beach detecting, I will first attempt high frequency, high gain operation and then back off as ground or EMI conditions require. One thing it is important to know when running the Impact with large coils is how the gain control works. If the Impact is running at Gain levels that are too high, the OVERLOAD message will appear on the screen. Note: You can increase or decrease the overload volume with the on/off button. When the volume of the device is at maximum, the overload volume will be low. As the volume of the device is lowered, the overload volume will increase. The electronic Gain has at least three distinct levels. There are distinct boosts between settings of 39 and 40 plus again between 69 and 70. Settings over 90 are a sort of hyper-Gain region only obtainable in low mineral/low EMI environments.
Therefore I may attempt to start out in 20 kHz and a very high Gain. If overloading occurs I will lower the Gain for smooth operation, paying particular attention when I get down to 69.
From there on down I need more field time, but at some point it will be better to drop to a lower frequency than to continue to lower the Gain setting. So in theory if at a setting of Gain 39 I still have issues at 20 kHz, it is time to go to 14 khz and run the Gain back up high. If conditions are still not amenable to running at 14 kHz and high Gain settings, I would then drop to 5 kHz and again attempt to run higher Gain levels. Note: people hunting larger, higher conductive items like silver coins and brass relics may very well just start out at 5 kHz. My focus is usually on lower conductive, smaller items i.e. gold.
I so far have only done a small amount of detecting in a local park. I first tried Di3 and while it was working well enough the trash density was high and interpreting signals with a large DD coil can be challenging, especially when the coil generates multiple signals on very shallow items. I finally went to the unique GEN(D) mode and it was night and day. The GEN(D) all metal mode combined with the VCO effect makes sizing targets and identifying shallow targets a breeze, even in a trashy park situation. Shallow ferrous is easily identified also using GEN(D).
There are several all metal modes a person can employ on the Impact as well as the extended range ground balance available in the COG (COnductive Ground). While the Impact performs ground balance in the range of 20-90 automatically in the other discrimination modes, it ground balances in the range of 0-90 in the COG mode. This enables easier ground balancing on conductive grounds where normally ground balance cannot be performed at all or performed with difficulty, such as salt water beaches. Remember that ground balancing to salt conditions always comes at the cost of reduced sensitivity to small gold items.
There is more I could mention about this subject but I really need time to get the hours on the Impact running the large coil to get more into specifics about how to get the best performance out of it. Large coil VLF hunting is not for everyone and is not a magic bullet in any case, but it does offer possibilities for the more adventuresome detectorist. I will close with a picture of my Nokta Impact with new IM40 coil. The detector with this coil is only slightly nose heavy (keep the rod as short as possible) and weighs with batteries 5 lbs 2.0 oz (5.13 lbs) or 2322 grams.
In general I think I can speak for most people when I say we all like lighter weight detectors. However, one area where lighter is not better is when you use large coils. Balance is every bit as important as weight as it determines the amount of torque applied to your wrist as you swing the detector. A large coil on a very light detector creates a very nose heavy detector, one that will put more strain on you when you detect than a heavier but better balanced detector. It just so happens that the Impact with the rear mounted battery power/speaker module is a good design for a large coil from an ergonomics standpoint. This is especially true when in my experience Nokta has designed large coils that are quite light for their size. I was probably one of the first people that really zeroed in on the new IM40 15" x 14" DD coil when it was proposed for the Impact by Nokta. I got on an early wait list for the coil, and just received mine.
The IM40 DD coil measures 15.5" x 13.75" and comes with a fitted skid plate/scuff cover. The coil weighs 1 lb 13.0 oz or 822 grams as pictured with skid plate and cable and weighed on my postal scales. Yes, I had to say that as some people exclude cable weights from coils! For comparison the stock 11" x 7" IMP29 coil weighs 15.7 oz or 446 grams. I like the flat blunted ends on the IM40, which does help the Impact stay upright as the trailing edge of the coil acts as a flat bearing surface when the detector is at rest on the ground.
I am not usually a fan of larger coils and in fact tend to lean to smaller coils for a lot of my urban metal detecting. Large coils "see" more area which can work against them in highly mineralized ground or in areas with lots of closely spaced trash. However, large coils even if they do not get more depth in highly mineralized ground can cover more area faster, and often ground coverage is every bit as important if not more so than depth. In medium to lower mineral ground a large coil can also offer that magic thing all detectorists crave - more depth!
The Nokta Impact has another trick up its sleeve that favors large coils; the ability to change operating frequency on the fly. High frequencies offer more sensitivity to small items and quicker separation in dense trash as well as extended battery operating time. The main issue with higher frequencies is they also "light up" highly mineralized ground and hot rocks more so than lower frequencies. This can work against machines that are locked into higher frequencies when attempting to employ large coils in highly mineralized ground. Lower frequencies give up some of the high frequency "hots" on small targets but also are less sensitive to ground issues, including salt mineralization. The ability of the Nokta Impact to run at 20 kHz, 14 kHz, or even 5 kHz makes it very well suited for running very large coils. This is accentuated by the plethora of all metal modes available on the Nokta Impact which can deliver extreme performance when coupled with a large coil.
The bottom line is I think the Nokta Impact and IM40 coil may be one of the very best options available for a person wanting to run a large coil on a VLF detector, with depths in all metal modes and milder ground that will challenge many PI detectors.
For a lot of what I personally do, like gold prospecting or beach detecting, I will first attempt high frequency, high gain operation and then back off as ground or EMI conditions require. One thing it is important to know when running the Impact with large coils is how the gain control works. If the Impact is running at Gain levels that are too high, the OVERLOAD message will appear on the screen. Note: You can increase or decrease the overload volume with the on/off button. When the volume of the device is at maximum, the overload volume will be low. As the volume of the device is lowered, the overload volume will increase. The electronic Gain has at least three distinct levels. There are distinct boosts between settings of 39 and 40 plus again between 69 and 70. Settings over 90 are a sort of hyper-Gain region only obtainable in low mineral/low EMI environments.
Therefore I may attempt to start out in 20 kHz and a very high Gain. If overloading occurs I will lower the Gain for smooth operation, paying particular attention when I get down to 69.
From there on down I need more field time, but at some point it will be better to drop to a lower frequency than to continue to lower the Gain setting. So in theory if at a setting of Gain 39 I still have issues at 20 kHz, it is time to go to 14 khz and run the Gain back up high. If conditions are still not amenable to running at 14 kHz and high Gain settings, I would then drop to 5 kHz and again attempt to run higher Gain levels. Note: people hunting larger, higher conductive items like silver coins and brass relics may very well just start out at 5 kHz. My focus is usually on lower conductive, smaller items i.e. gold.
I so far have only done a small amount of detecting in a local park. I first tried Di3 and while it was working well enough the trash density was high and interpreting signals with a large DD coil can be challenging, especially when the coil generates multiple signals on very shallow items. I finally went to the unique GEN(D) mode and it was night and day. The GEN(D) all metal mode combined with the VCO effect makes sizing targets and identifying shallow targets a breeze, even in a trashy park situation. Shallow ferrous is easily identified also using GEN(D).
There are several all metal modes a person can employ on the Impact as well as the extended range ground balance available in the COG (COnductive Ground). While the Impact performs ground balance in the range of 20-90 automatically in the other discrimination modes, it ground balances in the range of 0-90 in the COG mode. This enables easier ground balancing on conductive grounds where normally ground balance cannot be performed at all or performed with difficulty, such as salt water beaches. Remember that ground balancing to salt conditions always comes at the cost of reduced sensitivity to small gold items.
There is more I could mention about this subject but I really need time to get the hours on the Impact running the large coil to get more into specifics about how to get the best performance out of it. Large coil VLF hunting is not for everyone and is not a magic bullet in any case, but it does offer possibilities for the more adventuresome detectorist. I will close with a picture of my Nokta Impact with new IM40 coil. The detector with this coil is only slightly nose heavy (keep the rod as short as possible) and weighs with batteries 5 lbs 2.0 oz (5.13 lbs) or 2322 grams.
