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Concentric Versus DD Coils On White's MXT


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7 hours ago, auminesweeper said:

I try to run a concentric as much as possible and where the 9.5/950 might struggle with hotter ground the 5.3 is more tolerable because it see's a lot less ground than the 9.5 and not only that what the 6x4 see's at 1" the 5.3 will see at 2.5 to 3", Add that to how it ID's things better when the junk is pretty thick means I am not loosing targets due to using too much disc.

Was talking to my sister yesterday (she has an MXT w/10" DD and 4"x6" DD).  She said she was headed to a construction site with lots of rubble (rocks, dirt clods, piles of excavated ground) and wondered which to use?  She lives in Colorado which, in my limited experience, has just moderate ground in the parks and school-yards.  With your timely post, I'm wondering if the 5.3" Eclipse is the solution.  No more head scratching; just post here and get good answers!

Second question -- I cut and pasted this Dave Johnson quote from Steve's excellent review of the MXT here (Equipment Review sub-site): 

"Back in the late 1990's and very early 20th century, the MXT was developed around the 10x6 elliptical DD. When you're used to that searchcoil, stick a 950 on and the 950 feels downright clumsy with its muddy response and bad masking characteristics. Downright insufferable. The 950 searchcoil geometry was designed for completely different platforms.

But, if you ask "does the 950 work?", well, yeah, it does. Wrong question.

Sometimes engineers/designers view things from a different 'angle' than end-users.  You obviously like the 950 coil on the MXT.  Care to comment?

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Sorry Mate I just wrote a report and my computer just eat it, £%$& it,

So I will try again, 10"DD Vs 9.5/950.

the claimed figures for the 10"DD 17.9oz/507.45g actual figures = 23.670oz/671.10 grams =5.77oz heavier/163.65grams

the claimed figures for the 9.5 (Con) 18.4oz/521.63g actual figures = 20.617oz/593.0 grams = 2.217oz/71.73grams

figures for the older 950 coil 18.931oz/536.70grams = 4.7 ounces/134.40 grams lighter than the 10"DD,

If I am going to use a DD then I prefer the Detech 14x10 because not only does it cover more ground but it has much better balance than the 10"DD and I bought 2 of them because one weighs about 5 or 10 grams lighter than the 10"DD and one weighs the same But the bonus is that it gives quite a few inches more depth. and again the balance is great, where as the 10"DD makes the machine feel nose heavy.

As for the 4x6, One would think that for a small coil that it would be able to see smaller things, well it "can't", It is no more sensitive than the 6x10DD. Now as for the depth 4x6 = 4"+6"=10" / 2 =5" so 5 maybe 6 inches is the most depth that you can expect from a DD of that size on Coin sized targets,, It's a well known fact that a Concentric can and will achieve up to 1.5 times it's size In Depth , Some claim as much as 2X the size. I prefer to error on the side of caution and say that 1.3x the size is more realistic, so with the 5.3 (6") Coil the 6" X 1.3 = 7.8" but 8 to 9" depth is not unheard of on coin sized targets when using the 5.3 Coil.

The 4x6 has been the go to coil for Snipping etc but when you compare it's sensitivity to that of the 5.3 it is blind as a Bat. Where the 4x6 will struggle to see bits any smaller than 0.03 to 0.02 grams on the surface, The 5.3 will see bits down to 0.006/0.003 grams "or" 0.0002oz and 0.0001oz which is close to the size of two Sugar grains., So the 5.3  has at leased 2 or 3 inches more depth on coin sized targets but on tiny nugget type targets it is also 3x hotter than the 4x6, because what the 4x6 see's at 1 inch the 5.3 will see at 2.5 to 3 inches. and because it is so small mineralization does not seem to worry the machine as much as the larger concentric's.

So what are the benefits 1) weight is a major factor with the MXT/DFX/V3i where coil choice  can add almost Half a pound in weight to the machine not including the 12"/300mm Coil and as a side note as these coils have been released the above machines have got heavier and heavier which gets stated more and more these days. 2) the depth can be up to as much as 1.5x deeper than it's size. 3) the sensitivity of the smaller Coils really come in to their own, hence why the GB II is still the King of the specks. and 4) EMI does not seem to bother the machine as bad when running the machine up at Max levels.

Don't get me wrong DD's are great coils but picking the right time to deploy them is one of the most misused or misunderstood things about coils. Like I said before if your GND meter is reading from the mid 70's IE 75 to 78ish then that is the time you might start thinking about using a DD, But anything below that you are loosing depth because DD's only come in to their own when ground really hots up, you only have to watch GPX users to see that, because most of the time they want the depth and sensitivity that Mono Coils offer, And a Concentric Coil is a VLF's version of a Mono.

hope that helps.

John.

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My vote would also go for the 5.3 coil i use one on my DFX and it's deadly on really trashy saxon sites,why its called a 5.3 seem to baffle alot of folks but its not actually 5.3'' it is a 6'' coil,possibly one of the windings in side is that size but most folks call a coil by its coil case size but this is not the case with the 5.3.

Just had the combine on one of my permissions right at the bottom of my garden about 100 acres,so till christmas time will be hitting this field hard as it will be the last time till the new housing estate is built on it next year,the stubble is soft barley stubble so the best tool for the job will be either the DFX with the 5.3 coil or the T2 with the 5'' coil on,both will allow me too get right down to the ground in between the stubble rows.

Tomorrow is a lovely sunny day so guess what i plan on doing most of the day :smile::smile:

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A while ago I weighed the MXT and it proved to weigh a lot more than the factory claimed weight, Which is not an Issue for me because If I like it I will use it, But you can lighten the MXT by quite a large amount just by Coil and Battery selection alone without voiding your warranty,

Assuming that you can get away with using the 9.5 or the (Better/Lighter) older 950 Coil, We already know that the 950 weighs 4.7oz/134.40 grams lighter than the 10"DD, Well battery selection can also reduce the overall weight, using and off the shelf generic Alkali Battery brand weighing as little as 23.916 grams/0.843602oz X 8 = 191.328g or 6.748oz

Now using NiMh batteries, 1x AA = 30.031g/1.0593oz X 8 = 8.4744988oz / 248.24g. Add the weight of the 10"DD

the difference between the two types of batteries Is, 48.92g / 1.7264944oz.

Now add that weight to the weight difference of the Coil So 48.92g +134.40g = 183.32 or 6.466 Ounces Lighter.

Now Get it wrong and you will see a massive weight difference, As much as 191.302g / 6.748oz which is the same as removing the standard battery pack when fitted with the 10"DD,, REMEMBERING how many Ounces there are to a pound

Although Air Tests don't mean much these days But the 10"DD Coil breaks the rules in that it Air Tests as good as the 950 Concentric So again unless you have fairly hot ground then you are loosing nothing by switching to the 950 coil or the 10"DD. but you are saving a lot of weight along with using less disc, less EMI, better Iron ID etc.

Think about batteries for a second,, if you use NiMh batteries and charge them up, The MXT uses such a small amount of power that unless you are detecting 24/7 then the next time you use the machine there is a good chance that they will be flat,  and then you have to waste another day charging them back up, But by using Duracells or Energizer's you will get over 60 hours out of a set, One thing we see a lot of is when people are posting how their brand of machine runs for 20 or 30 hours using 4 AA's and yes that is good But the MXT will run for over 60 hours using 8 AA's so it is six of one and half a dozen of another, Running Duracell/Energizer's will hold their charge just make sure you don't leave them in the machine or bad things can happen, Using NiMh batteries in machines like the MXT is a very Grey area due to the power consumption and their weight and to be honest I only ever use them when testing or for the TDI SL.

So if your MXT is over weight just take another look at the Coil and batteries you are using.

food for thought, Aye ?

John.

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@auminesweeper,John,i use the RNB battery pack in my DFX and IDX Pro,is a fair amount lighter than either the rechargeable pack or the alkaline battery case as well,i do carry a spare pod and batteries in a spare pack just incase anything was too happen,but as yet never needed to use it.

 

 

 

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Yeah Rick, they a great battery packs but I would not use them In any of the E-Series machines because they can put out well over 14 volts which is a bit risky because there is very little known about what the limits are in the E-Series machines, Where as Duracells and Energizers can put out 12,6 to 13.0 volts +/- and Energizer Ultra lithium's can put out 1.84/1.87 volts per cell which is 14.72 volts to 14.96 volts which is a 25% increase in power on the input side of things, These machines were made with the current Battery tech in mind back in the 90's /00's and these newer batteries are tempting fate, "Yes" they will work but for how long ? that is the question,

The V3i and the TDI SL are battery hog's and the SL has a bit more wiggle room when it comes to Voltage but the older E-Series are voltage controlled and have much tighter tolerances so over powering them is not a risk I would be taking. Unlike the SL the E-Series does not benefit from the higher voltage,

I was playing with an LED Lantern and I saw it had a charging point/plug socket, being fed up with cranking the handle I pluged it in to a power adapter and it was charging good, and after a few minutes it started to get warm and every thing was fine but after about 30 minutes it melted the solder and the wire to the charging circuit became un-attached,, The thing I am pointing out is that if you go putting to much power in to the MXT/DFX you stand a good chance of melting the solder joints where the battery Tabs on the circuit board are soldered to the board, I repaired the Lantern and now I use a solar charger hooked up and it is always ready for action and no more worries, personally I would I would not use the RNB in anything but the TDI SL because it is adding about 33% more voltage and where there is voltage there is Heat and although you can't feel it buried within that big metal box does not mean it is not there, so just be careful, Ok.

John. 

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John,i take your point about the RNB battery pack,but in the case of the DFX have been using it for over 2 years and never had any problem thus far,my way of thinking that if anything was too go wrong it would have done all ready,over 2 years is alot longer than a small lanter of just 30 minutes use,the IDX Pro is of course alot older than the DFX and have also not noticed any problems again.

It would be 'sods law' that when i go out tomorrow for the day detecting something will fail,but this is why i always carry a backup or 2,just incase did happen while i am away on a dig.

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Rick I don't see anything wrong with the RNB packs because I think they are great, But I have just got my A/P doing / behaving as I knew it could and knowing my luck it would not end well, If I want more power then I just change Coils.

I don't post  about the power of the Coils but they can see from grains of sand sized items to huge things way down deep,  And that 14x10 will have a person digging way deeper than they want only to find a Beer Can, so heaven forbid what a large paint or Gerry can would come up at, I have already dug a small toy soldier at 17" using 10"DD on my old Sov GT and the 14x10 can be Brutal when it comes to depth.

The RNB as far as the TDI SL is concerned is a must have Item because the hardware is built in to the SL in order to run the RNB packs but as yet I have not managed to get my hands on one for the SL, But as soon as the truck is sorted I will get my hands on one.

John. 

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26 minutes ago, auminesweeper said:

Yeah Rick, they a great battery packs but I would not use them In any of the E-Series machines because they can put out well over 14 volts which is a bit risky because there is very little known about what the limits are in the E-Series machines, Where as Duracells and Energizers can put out 12,6 to 13.0 volts +/- and Energizer Ultra lithium's can put out 1.84/1.87 volts per cell which is 14.72 volts to 14.96 volts which is a 25% increase in power on the input side of things, These machines were made with the current Battery tech in mind back in the 90's /00's and these newer batteries are tempting fate, "Yes" they will work but for how long ? that is the question,

The V3i and the TDI SL are battery hog's and the SL has a bit more wiggle room when it comes to Voltage but the older E-Series are voltage controlled and have much tighter tolerances so over powering them is not a risk I would be taking. Unlike the SL the E-Series does not benefit from the higher voltage,

I was playing with an LED Lantern and I saw it had a charging point/plug socket, being fed up with cranking the handle I pluged it in to a power adapter and it was charging good, and after a few minutes it started to get warm and every thing was fine but after about 30 minutes it melted the solder and the wire to the charging circuit became un-attached,, The thing I am pointing out is that if you go putting to much power in to the MXT/DFX you stand a good chance of melting the solder joints where the battery Tabs on the circuit board are soldered to the board, I repaired the Lantern and now I use a solar charger hooked up and it is always ready for action and no more worries, personally I would I would not use the RNB in anything but the TDI SL because it is adding about 33% more voltage and where there is voltage there is Heat and although you can't feel it buried within that big metal box does not mean it is not there, so just be careful, Ok.

John. 

John, the RNB packs for the GMT, DFX, MXT, etc. are 3-cell packs. max voltage is 12.6...perfectly safe in those models. RNB doesn't make a 4-cell pack in that configuration. To my knowledge, the only person making, and selling the 4-cell pack is Reidman. You defintely don't want to put a 4-cell pack in the aforementioned detectors, but it works terrific in the TDISL.

Jim

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Cool Jim, and good to see you, you handsome devil.

Jim, to be honest I only knew of the hi power version that fits the TDI SL, which is why I was a bit concerned, I can't count the times I've wished that I had left well enough alone, Me and Murphy's Law have some explaining to do and we don't see eye to eye, lol.

I will check out the other packs when I get time so thanks for that.

John.

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