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Nokta Impact And New 15"x14" IM40 Coil
Posted by: steve herschbach
Date: May 30, 2017 10:31AM
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.





Minelab GPZ 7000, Gold Monster 1000, Equinox 800; Garrett ATX; Makro Gold Racer; White's V3i/Bigfoot; Garrett Carrot; Sun Ray Pro Gold



Edited 1 time(s). Last edit at 05/30/2017 10:59AM by steve herschbach.


Re: Nokta Impact And New 15"x14" IM40 Coil
Posted by: Beyonder
Date: May 30, 2017 11:05AM
Impressive write-up Steve as usual! Thanks for taking the time!

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Re: Nokta Impact And New 15"x14" IM40 Coil
Posted by: Cal_Cobra
Date: May 30, 2017 03:02PM
Steve thanks for sharing your findings on the impressively sized IM40 Impact coil !!

I've found 20Khz to be my go to frequency. The couple of places I've attempted to run 5Khz, EMI prevented it's use, whereas 20Khz ran fine. I'd really like to run 5Khz for deep silver detecting, so hopefully other sites will allow it. Your notes on the GEN(D) mode are good info, that's definitely a mode I'll try a couple of sites that it seems like it might be beneficial at. I wonder if it's deeper then DI3? DI3 is also turning out to be my go to tone mode.

hh,
Cal

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Re: Nokta Impact And New 15"x14" IM40 Coil
Posted by: steve herschbach
Date: May 30, 2017 07:54PM
GEN(D) is one of the four "all metal" modes on the Impact and in theory these are the deepest seeking modes.

From Nokta Impact Owners Manual, pages 12-13:

Static Mode (STA)

This is a non-motion mode. In other words, the device will generate an audio response when you hold the coil stationary without swinging over the target. The audio response increases in volume as the coil approaches the target. This mode is recommended for larger and deeper metals.

In the STA mode, the device will generate the same audio tone for all metals and it will display the target ID on screen. At the same time, the ID scale will fill up to the right in proportion to the signal strength.

Target ID range is 00-99. 00-40 are ferrous and 41-99 are non-ferrous metals. You can discriminate out all IDs below a certain ID by using the Disc. setting and simply avoid these metals in the field.

When the device detects a discriminated metal, it will not produce an audio response or an ID. However, the ID scale will fill up to the right in proportion to the signal strength.

The threshold in this mode is internal and cannot be adjusted by the user. Changes in the ground and temperature may lead to drifts in the threshold. Threshold drifts will be reflected in the ID scale either in the positive way (right side) or the negative way (left side). The device may emit an audible response in the positive drifts but not in the negative ones. When the threshold drifts, pull the trigger once to retune the detector. Retuning periodically while searching in this mode is recommended.

IMPORTANT! For a more stable operation, try keeping the coil consistently at the same height above the ground where you retuned the detector.

IMPORTANT! If you retune the detector over a target, the threshold will drift to the negative side and the device will no longer detect the target until the detector is retuned. In addition, the depth of the detector will also decrease.

If the drifts are substantial and retuning does not improve the situation, increase the iSAT setting in the Expert Settings to a level where the drifts are eliminated (for detailed informa- tion on iSAT please refer to page 24). As the iSAT is increased, the device may detect weaker signals but will not be able to detect the targets anymore if you hold the coil stationary or sweep back and forth over the target. If the drifts still continue frequently, drop the gain to 39, decrease the iSAT and re-ground balance.

Static Delta Mode (STA (D))

In principle, it works the same as the static mode. The difference is that the static delta mode will generate the same tone for ferrous and non-ferrous targets at fringe depths but it will discriminate the shallow ferrous targets by emitting a low iron tone. Also, Disc. setting is not available in this mode.

Please refer to Table 2 at the end of the manual for different settings used in STA and STA (D) modes.

General Search (GEN)

Different than the other modes, this mode features a threshold tone which is continuously heard in the background.

General Search (GEN) mode is used in 2 different ways in the IMPACT: 1) with the Disc. setting disabled at 0 2) with Disc. enabled (non-zero). When the device is first turned on, Disc. setting will be off. When the Disc. is set at 0, the device does not discriminate targets and detects all targets (metals, mineralized rocks etc.). ID of the detected target is shown on the display (except for negative hot rocks) and the same audio tone is provided for all targets. The audio tone increases in pitch as the coil approaches the target. This is the typical All Metal mode found in most detectors.

When using the Disc. Setting in this mode, the device will emit a low ferrous tone for all targets below the Disc. Setting, and a higher tone for all targets above the Disc. setting which changes in pitch as the coil approaches the target. Let's say you set the Disc. to 20. The device will generate a low iron tone for all metals with 0-20 ID and a higher tone for all targets with 21-99 ID. Upon target detection, the threshold will momentarily go silent and only the target audio response will be heard. The duration of the threshold's silence is directly related to the level of the iSAT.

Gain, threshold and iSAT settings in this mode are optimized to provide the best perfor- mance on different terrains. You can modify these settings based on ground conditions.

We recommend using the GEN mode when discrimination is not important and not using it in heavy trash areas or areas containing many hot rocks.

Audio Boost in the General Search Mode
This feature is not included in the settings on screen. Boosts the sound of weak signals received from small or deep targets making it easier for you to detect those uncertain targets. It is recommended that audio boost should be used on a temporary or as-needed basis because it will not only boost the target signal audio but it will also boost the volume of ground noise and false signals along with the threshold hum.

Audio Boost consists of 5 levels (b1-b5). At start up, the Audio Boost level is set to low (b1). To increase the Audio Boost level, pull the trigger and press the minus (-) button simultaneously. Audio Boost will only work in the GEN mode.

General Search Delta (GEN (D))

In principle, it works the same as GEN mode. The difference is that the Gen (D) mode will generate the same tone for ferrous and non-ferrous targets at fringe depths but it will discriminate the shallow ferrous targets by emitting a low iron tone.



Minelab GPZ 7000, Gold Monster 1000, Equinox 800; Garrett ATX; Makro Gold Racer; White's V3i/Bigfoot; Garrett Carrot; Sun Ray Pro Gold

Re: Nokta Impact And New 15"x14" IM40 Coil
Posted by: dbado1
Date: May 30, 2017 11:17PM
Thanks, Steve! Great write up.
I like Gen(D) in areas that aren't too trashy. Gives me audio overload if there is too much trash.
I took the Impact nugget shooting the other day to a patch that we have hammered with the GPX, SDC, and Gold Racer. No gold for me on this hunt, but the Impact performed well in Gen mode picking up tiny bird shot and fragments of bird shot in moderately mineralized ground. It easily identified hot rocks with recognizable "hot rock" tones and bird shot was a nice sharp "zip-zip". Great distinction. No mistaking the differences. I really like the tonal qualities of the Impact. I don't do a lot of nugget shooting with a VLF anymore but I feel that the Impact is a very capable VLF nugget machine.

The large coil looks to be a welcomed addition to the Impact coil line. Thanks again!

Dean

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Re: Nokta Impact And New 15"x14" IM40 Coil
Posted by: Mudwhale
Date: May 31, 2017 05:58PM
Great info Steve!!! I am a new Impact owner...
Cheers Ed

Re: Nokta Impact And New 15"x14" IM40 Coil
Posted by: CCadrin
Date: May 31, 2017 08:48PM
Quote
Mudwhale
Great info Steve!!! I am a new Impact owner...
Cheers Ed

Ed, have you been out with the Impact yet? This is charly-in-ct-ri from from the other forum.

Re: Nokta Impact And New 15"x14" IM40 Coil
Posted by: NCtoad
Date: June 03, 2017 02:25PM
Wow, thanks for sharing your knowledge! I'm a new detectorist and don't even own a Nokta, but found the information you posted on coil size and frequencies very interesting and helpful.

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Re: Nokta Impact And New 15"x14" IM40 Coil
Posted by: Mudwhale
Date: June 16, 2017 05:03PM
Quote
CCadrin
Quote
Mudwhale
Great info Steve!!! I am a new Impact owner...
Cheers Ed

Ed, have you been out with the Impact yet? This is charly-in-ct-ri from from the other forum.

Sorry for the Lapse Charly! Yes I have been out hunting and getting used to the machine. Coming from an ATP and an ETRAC it's a learning curve but when I finally get used to it I think it will be my favorite weapon of choice. My best find so far is a tiny St Christopher in the deep woods at about 7". It's only 8K but it was deep, banged hard and was not a pull tab...




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Re: Nokta Impact And New 15"x14" IM40 Coil
Posted by: Stoof-tabsallday
Date: June 22, 2017 09:47PM
You guys are really making it hard not to buy an impact.... Lol



Stefan (Michigan)

Nokta Fors Relic 7x11", 5.5x10"DD, 5", 5.5x10 Concentric


Makro Racer 2 - 7x11", 5.5x10", 5" DD


:tesoro: Mojave
:tesoro: Deleon - Troy shadow super 7",
:tesoro: Compadre 8
:tesoro: Compadre 5.75
:tesoro: Bandido II Micromax
:tesoro: Outlaw
:tesoro: Cibola- GB/all metal toggle mod
:tesoro: Vaquero
:tesoro: Cutlass Micromax 8

Lots of coils

*Not listed in any special order*

Tools:
Garrett carrot, lesche shovel, Killer B Wasps, my bare hands

Re: Nokta Impact And New 15"x14" IM40 Coil
Posted by: alecoman
Date: June 26, 2017 03:54PM
Hi Steve

Since you hunt gold nuggets and got the Impact..
Could you share with us the VDI reading on 1 and 2 grams nugget in DI2 and Deep mode if that is possible.
I tried on a few specs that i have which add up to less than 0.5 grams in total.
Got those two modes to give me a vdi reading but not the others.
I got 18 to 16 on DI2 and 45 to 41 on Deep .. 20khz / 95 gain air test with the IM19 coil.

Thanks in advance.

Re: Nokta Impact And New 15"x14" IM40 Coil
Posted by: synthnut
Date: June 28, 2017 08:05AM
When I saw the ad mentioning "multi frequencies " , I have to admit it caught my eye ....... After readiing more threads on this machine , I see it's still a single freq machine as the frequencies are chosen individually and do not run all inclusively ......IT's more a case of OR rather than AND ....... That alone will keep me on my other inclusive frequency machines as I do a lot of beach hunting .....GREAT job on the write up though ..... Good read !!.....Jim

Re: Nokta Impact And New 15"x14" IM40 Coil
Posted by: shelton7522
Date: August 31, 2017 12:45AM
Good job. In my opinion with big coil you should remember about low mineralized soil and low EMI place. Both values too high and even with middle range of gain we get high noise from ground. Too much information. So with this coil we should work on lower gain in this situation.

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Re: Nokta Impact And New 15"x14" IM40 Coil
Posted by: steve herschbach
Date: September 02, 2017 09:40PM
Quote
alecoman
Hi Steve

Since you hunt gold nuggets and got the Impact..
Could you share with us the VDI reading on 1 and 2 grams nugget in DI2 and Deep mode if that is possible.
I tried on a few specs that i have which add up to less than 0.5 grams in total.
Got those two modes to give me a vdi reading but not the others.
I got 18 to 16 on DI2 and 45 to 41 on Deep .. 20khz / 95 gain air test with the IM19 coil.

Thanks in advance.

Hi,

Sorry I missed your question earlier - and it may be you never see the answer now a couple months later. But here goes anyway.

This by accident may be very informative possibly for people who do not know exactly how VDI numbers are generated. The short story is they are a combination of the target conductivity and the size of the target. In other words, silver is more conductive than lead, so two identical items, one made of lead and the other silver, the silver item will have a much higher VDI number.

For two items made of silver (or lead, gold, whatever) where one item is larger than the other, the larger item will generally have higher VDI numbers.

The Nokta Impact is unique as far as I know in that it has two different target id (VDI) number scales that are used in the various modes. The Impact VDI scale runs from 0 - 99 but as I said there are two different ways the scale is divided. One set of modes uses 0 - 15 as ferrous, all else non-ferrous. The other modes use 0 - 40 as ferrous, all else non-ferrous, expanding the ferrous range.

I did not want to sort nuggets all night so came up with a 0.90 gram nugget and a 2.03 gram nugget, both from the same Nevada location, and both of similar shape although one is obviously larger than the other. Here are the results...



The 0.90 gram nugget using the DI2 0 - 15 equals ferrous scale has a VDI number of 37. The same nugget in the Deep 0 - 40 equals ferrous scale reads 63.

The 2.03 gram nugget using the DI2 0 - 15 equals ferrous scale has a VDI number of 32. The same nugget in the Deep 0 - 40 equals ferrous scale reads 56.

Here we have a smaller gold item giving a higher VDI number than a larger gold item. How do we explain these results?

Gold nuggets are not pure gold. These nuggets are probably around 85% - 90% gold. The rest is mostly silver. Here is a strange fact. Silver is more conductive than gold. You would think adding silver to gold would raise the VDI number. However, reality is pure metals conduct electricity better than alloys, and so adding silver to gold actually lowers the conductivity and therefore the VDI numbers. In this case the size, shape, and most importantly, alloy composition of the larger nugget is causing it to read lower than the smaller nugget.

This is a great example of why if you are looking for gold nuggets you at a minimum dig all non-ferrous targets. And because weak nugget signals (very small nuggets or large nuggets deep) in mineralized ground can read as ferrous, the only truly safe approach is to dig everything.

Here is a photo of a large variety of gold nuggets and some coins I tested with the White's DFX, which uses the same -95 to 95 scale as many White's detectors. Again, you can see that size and VDI numbers do not correlate due to shape and purity differences. In general the paler gold has higher silver content.





Minelab GPZ 7000, Gold Monster 1000, Equinox 800; Garrett ATX; Makro Gold Racer; White's V3i/Bigfoot; Garrett Carrot; Sun Ray Pro Gold


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