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I like the Ground Phase on the MXT's, Although it can be used to follow the black sand "50" is the mid way point/starting point So a GND reading of 86 is fairly hot but also a reading of 14 is equally hot because they are both +/- 36 of the 50,  Numbers above 50 relates to the amount of Iron Oxides present and numbers below 50 indicate the amount of Alkali's (Salt) are present, with this system or any other for that matter can help you decide which coil type or size would be the best option, More so when in ground with lower numbers because detectors loose sensitivity the further the numbers dip below 50 So that is the time to deploy something like a small concentric in order to recoup some of the lost sensitivity.

High GND numbers are a double edge sword and can bite you on the rump, Because for one you have to drop the gain and the bigger the coil the lower you have to go, People often blame the Ground for this but ? in a way it is to blame but when your detector picks a high Ground Phase number to suit the ground conditions, It actually makes the detector very sensitive to tiny bits of metal and ground conditions, You can prove this to your self, If you own a Whites machine or and MXT/GMT get your self an 0.02 gm bit of lead and stick it to a ruler and set the machine in tracking and turn it on and once it has fired up then lock the GB and the GND meter will be locked to 50 now max out the gain and wave the bit of lead in front of the coil and if you are lucky the machine should just about pick it up,  and make a note of the distance, Then shut the machine off and leave the tracking locked and switch the machine back on so it's GND/ground phase reads 85/86 and max out the gain and wave the bit of lead in front of the coil again and check the distance and compare the two tests.

The change in distances between the two is quite a bit, When out in the wilds and your GB is reading in the high 80's the machine is going to tell you to turn it down so you are going to loose depth and sensitivity and the only way to redeem some of the sensitivity is to go to a coil like the 5.3 and work the gain back up until the machine starts to get noisy and back it off just a touch. If you want to find the small stuff with a VLF in hot ground then forget the 6x10's and go smaller because the smaller the coil the less ground the machine see's and the higher you can run your Gain, Mix that high Gain with the high GND/Ground Phase numbers = sensitivity to tiny Items helping you to use the higher GND/GP in your favour and in shallow bedrock and soil less that 8-10" deep you won't be missing much.

Air test don't mean much apart from show how different coils react But if you air test you machine at it's mid GB point and then up near it's higher limits you will have a good idea how it will respond to tiny bits in hot ground and if you back the gain down to 75%ish it will paint a better picture of real world usage,

hope that helps,


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On 8/9/2018 at 11:29 AM, EMField said:

I've always liked the fact that many of Dave Johnson's detector designs have ground mineralization, and Fe304 readouts.


9 hours ago, EMField said:

I think my favorite detector for providing the operator relevant information was the Fisher F5.

It's a general use detector at 7.8KHz, that does well on silver.

To tie your two posts/comments together, Dave J. also played a major roll (chief designer?) of the Fisher F5.  35+ years in the business and his trophy case of successful designs is difficult to ponder.  No doubt he has had help along the way.  First Texas had a crack staff even before Carl was hired.  If there were a Hall of Fame in detector designs Dave would be at the top of the inaugural class.


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3 hours ago, auminesweeper said:

I like the Ground Phase on the MXT's, Although it can be used to follow the black sand "50" is the mid way point/starting point So a GND reading of 86 is fairly hot but also a reading of 14 is equally hot because they are both +/- 36 of the 50,  Numbers above 50 relates to the amount of Iron Oxides present and numbers below 50 indicate the amount of Alkali's (Salt) are present

Actually this is completely wrong John. Ground Phase (the ground balance number) relates the TYPE of mineralization, not the AMOUNT. The is the entire reason Dave Johnson added the Fe3O4 meter to the GMT and many of his designs that followed. The MXT does not have this feature. That is not to say the TYPE of ground mineralization does not matter, but what you are saying directly contradicts Dave Johnson (and others - see link below), and in this matter my bet is on him.

GB Numbers = Mineralization?

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Some detectors have the ability to measure the Type ground-Ground phase number, ... but also the terrain mineralization power-Strenght mineralization size...at ground balance setting from my G2 detector-teknetics, Rutus Argo-6.6kHz, Rutus Optima-16khz, and most developed by Whites Spectra V3-in ground probe- there is the possibility to deduct the difference in the strength of mineralization at work in 3f versus 1f- result in percentage of force 3 frequency of mineralization in 3 frequency- is more or less the same as in the work on 1 frequency- so can multifrequency better work in mineralized ground....

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It was my understanding that Iron oxide was the base layer/ingredient for Iron, As in one of the three main ingredients of Iron. Fe2 o3, So I call it Iron Oxide because it is a lot easier to call it that or remember how to spell or pronounce  Magnetite  (ferrosic oxide) Fe304 OR Maghemite  Fe203(gamma ferric oxide) Both of which I copied from that link you posted. bottom line is they are all Iron variants, So I find it easier to stick them all under the one label.

When heated up like back when the big bang happened Fe2o3 then turned black and became Fe304 or Black Sand (magnetite).

QUOTE:- from Page 19 from MXT Pro/All Pro Manual.
B. Checking outcropping or veins, the ground phase
can also be useful in a similar way by indicating the
consistency or change of the veins ground phase.
Generally speaking, the ground numbers will hold fairly
consistent in most open terrain areas, such as hydraulic
sites and desert areas.

GND readings in the high 70’s and 80’s are considered heavy iron mineralization. Alkali or salt areas will display much lower numbers, possibly into the 30’s and 40’s.

NOTE- Watching the change in Ground Number in the upper right of the display, you will first look for a change to a high number indicating high mineralization or black sand. When that streak is identified you will then look for the Ground Number to lower again at one end of the streak indicating where the flour gold or gold ore may be concentrated.       End Quote.


Iron(III) oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare, and iron(II,III) oxide (Fe3O4), which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main source of iron for the steel industry. Fe2O3 is ferromagnetic, dark red, and readily attacked by acids. Iron(III) oxide is often called rust, and is acidic in nature and to some extent this label is useful, because rust shares several properties and has a similar composition. To a chemist, rust is considered an ill-defined material, described as hydrated ferric oxide.

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8 hours ago, Steve Herschbach said:

Actually this is completely wrong John. Ground Phase (the ground balance number) relates the TYPE of mineralization, not the AMOUNT. The is the entire reason Dave Johnson added the Fe3O4 meter to the GMT and many of his designs that followed. The MXT does not have this feature. That is not to say the TYPE of ground mineralization does not matter, but what you are saying directly contradicts Dave Johnson (and others - see link below), and in this matter my bet is on him.

GB Numbers = Mineralization?

Yes but numbers from 50 and Up mean Iron and the higher the number the worse the content, It does not mean how much there is just means that it is higher meaning Worse and below 50 means Alkali/Salt based and the lower it goes the worse it is, Although it is very rare to find levels where the numbers go below the 30's, I only picked those numbers 14/86 because they were equal parts but from the opposite end of the scale to each other. They are not measurements of how much Iron there is, Above 50 = Iron, Higher =Worse, Below 50 = Alkali and lower means = higher in Alkali. These figures do not relate directly to the Three scales below.

A number of 57 is quite low in Iron but a number of 84 should tell the user that the Iron content is quite strong, Any of these systems are only a guide and it gets confusing because the MXT uses half of what the GMT says via a GND reading, but if you run the 2 machines side by side the GND numbers do not match and then you have the three versions below, So with 5 variants all claiming to be a measurement of the ground it makes it impossible to know which is right, 

Whites has their GND and Disc scales as do Fisher and ML have their version and their disc showing Fe/Co and then there is the scales used by companies from the EU, The whole thing is a mess because there is no standard measurement, The Whites system seems to be the best with -95/+95 and the GND meter with Iron on the Disc being below Zero and Non Ferrous being above Zero. because zero being the starting point as with Speed whether it is MPH/KPH and Temperature and the list goes on, but when it comes to detectors the whole thing is a Mess.

0 – 10 Wet salt and alkali
5 – 25 Metallic iron. Very few soils in this range. You are probably over metal.
26–39 Very few soils in this range -- occasionally some saltwater beaches
40–75 Red, yellow and brown iron-bearing clay minerals
75–95 Magnetite and other black iron minerals

7 Bars -------- High over 1 over 2500
2 to 6 Bars -- Medium .026 - 1.0 61 - 2,500
1 Bar --------- Very Low 0.006 - .025 15 - 60
none -- less than .006 less than 15

3 --- 7,500 --- uncommon but not rare, heavy mineralization
1 --- 2,500 --- heavy mineralization, not uncommon in goldfields
0.3 --- 750 --- heavy mineralization, but not uncommon in some regions
0.1 --- 250 --- medium mineralization, typical
0.03 --- 75 --- light mineralization, but common
0.01 --- 25 --- light mineralization, often low G.C. setting
blank <14 --- quartz & coral white beach sands

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16 hours ago, GB_Amateur said:


To tie your two posts/comments together, Dave J. also played a major roll (chief designer?) of the Fisher F5.  35+ years in the business and his trophy case of successful designs is difficult to ponder.  No doubt he has had help along the way.  First Texas had a crack staff even before Carl was hired.  If there were a Hall of Fame in detector designs Dave would be at the top of the inaugural class.


I totally agree GB-A!

I think Jorge Saad was the lead guy on the F5 project, but as you said, DJ most likely had a "major roll".

Right now, there is a huge amount of detector design talent at First Texas.  With the addition of Carl Moreland as you mentioned, and their collaboration with the French physicist on their new Pulse Induction programs, I expect some pretty good stuff to come from that group in the near future.

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