conductivity

so how does the etrac(or any detector) exactly figure out the conductivity of a target? as the signal goes into the ground is it a change in the signal as it reflects back to the coil? i imagine that it is the same concept as sonar in salt water that figures depth the time between sent and recieved signals. but the whole concept of conductivty makes me question exactly why they cant boost the signal useing amplifiers in the coils? maybe i am way off the spot on this but just seems the adding an amplifier (or even a capsitor) to have a stronger signal would make sense. please add your thoughts. i have basic understanding of electrical concepts but just cant seem to find anything on the net that gives clear awnsers on the the way the machines honostly opperate internally and not really wanting to destray my detector i have now just to figure it out lol

OK, this is just me thinking, so it is not true facts. A detector determines a target id by the phase angle of the signal coming back to the receive coil. the type of metal determines this delay.
It is not so much conductivity as it is the ability to absorb the signal. thus increasing the delay. Precious metals that are pure can not become a magnet. So it has a shorter amount of time for the signal to be
returned to the coil. A ferrous target such as iron, can become a magnet. So as the signal hits the iron it will absorb the signal until be becomes saturated or the signal strength drops below it's charged level.
Thus this is causing a small delay in the signal back to the coil. A detector uses VLF which is a sinewave signal that is rising and falling based on the frequency. thousands of time per second. Now you are most
likely wondering how it determins a dime, quarter, penny. Each is a different size and metal compound that still gives a small amount of delay in signal phase.

It is like bouncing a ball, if you drop it on concrete ( silver coin) it will bounce back kinda fast, if you drop it on a rubber mat, (iron) it will bounce back but not as fast or as strong. The mat absorbs some of the energy until it becomes compressed, then it pushes the ball back up. Thus causing a time delay or greater phase angle.

Now again this is just me thinking and may not be correct................

Tom in SC

Minelab's website has some technical articles explaining how detectors work, and some of the methods they use.

I liked Tom's post as it sounded reasonable right or wrong...Actually I feel it varies a tad from manufacturer to manufacturer but of course just an opinion.

In addendum I drive my car to my hunting area and don't have a prayer how it works but of course we all differ and indeed knowing how your unit works could certainly help your detecting skills...

well my thought was this, if its an electrical signal then it can be manipulated! the depper the signal the weaker it is at the bottom or return area correct? why then is it not possable to add a capicitor to the coil with its own power supplky (still controled by the "head unit") to produce a signal double the strength but still the same freaquancy? wouldnt it make sense that the stronger the signal the more depth? take for instance radio waves ( from what i read its the same concept) if you amplify that signal you reach miles more, but no return. so in this case why not amplify the frequancy you want nullify the others and by my way of thinkiong (right or wrong) your looking at an additional 5 inches of target depth. i mean we can create smart phones and that reach thousands of miles useing relays but we cant make a machine that can detect a dime at 14 inches? seems like the tech. is there the willingness to use said tech is not. pulse induction does something similar but at 12k i doubt thats an option for most of us! with twin loop coils or even the double d cols with twice the width we still are only getting max of 11 to 12 inches on higher end machines ( again from my knowladge) i seriously thing that a multi phase capicitor with lets say a 12 volt power supply could infact be able to reach 15 inches given the right programming regardless of soil interferance or emi. i think that a single wrap transmitter and a double wrap coil could do just that. i myself think that multi frequancy detectors are capable already of this but have yet to figure out how exactly to get feedback elliminated to the "head unit".

Brain -- the "weak" signals of metal targets in the ground (relative to the ground signal) that are received by a receive coil ARE amplified, just as you mentioned. Gain adjustment helps the user control this to some degree...lowering gain will "silence" a weak signal, while raising gain will "amplify" it. On my Explorer, running gain at 10 means that all targets which the machine senses will be of the same volume, irrelevant of depth or size of target. The issue as I understand it is that transmit and receive signals the detector is using are attenuated by ground minerals, etc. Thus -- the deeper the target, the weaker the return, all else being equal. But, the ground signal is SO large, there comes a point for each detector when the several-orders-of-magnitude weaker target signal (as compared to the ground) simply cannot be reliably "recognized" or "separated out" from the ground signal -- and thus, there's nothing there for the machine to AMPLIFY (without also amplifying the ground signal -- which is useless and counter-productive, of course)

That's my understanding. I like to think of it in simple terms -- like person who is whispering, in a room with a fan running. If I am holding a microphone, hooked to a computer to record the person whispering, I will also be recording the fan noise. Running it through some software, I could "separate out" the person's whisper, and then amplify it electronically. But, as the person moves farther and farther from me, the whisper becomes increasingly hard to discern from amongst the background fan noise; still, as long as it can be "separated" from the fan noise, I (using my computer software) can isolate and amplify that whisper. At some point, the whisper is completely drowned out by the fan noise, and I reach a point where trying to find, separate, and amplify that whisper becomes impossible -- and thus there is a maximum distance at which I can "hear" the whisper -- DUE TO THE BACKGROUND NOISE. I have to be able to ISOLATE the whisper, before I can AMPLIFY it. While not perfect, this is one analogy that for my mind helps to illustrate the problem of detector depth limits. Better electronics can apparently help increase the depth SOME, but there is still a limit -- and NASA-Tom has said we have just about reached the limit that current technology (electromagnetic detection of in-ground metal targets on a magnetic, iron-dominated planet) can attain.

Steve

Keep it coming Steve....

Anyone that has dug in NE Pa. ground for deep targets would feel the same way as me as my units go as deep as I want to dig..

Gosh I watch some videos and ground sure is not like mine for digging deep.

I realize some of you relic hunters that hunt in the boonies carry a shovel and same goes for a sandy beach so indeed more depth would be a plus....

I think Tom has it pretty much right in that most that have read relates to phase and return signal strength being what is measured. I also have read that minelabs FBS can also get an idea of ferrous content as well. I have also read that the detectors are not really measuring conductivity or ferrous content but the data they do collect does correlate close enough to give us an idea of relative conductivity and ferrous content.

Now hear is some food for thought if there were one other physical property we could get a Realitive reading on which one would be the most useful. Size is an obvious one that with some skill we already have - note Garrett did have a detector that sized targets so doing this in the machine is not impossible because it has been done. How about density. If some how we could determine the Realitive density of a target along with its Realitive conductive and magnetic (ferrous) properties we may be able pass over a little more junk, a gold ring will have a lot more density then a pull tab or ball of foil.

Aloha

Bryanna

Very good reply Steve!!

And yes manufacturer's know this stuff..

And Brian the more Voltage you use will just barely increase depth...24 volts will not go double depth over 12 volt's...it might not go 1 inch more..Dave Johnson has explained this before...

Good thinking though

what we have to contend with is the laws of physics...VLFs are about tapped out...manufacturer's know this...they look for better ways to discriminate etc but depth is in other realms.....Different technology...maybe not in phase shift or conductance.. maybe in more like a ground penetrating M.R.I. machine..

see a true 3d image of ingroud target's to adepth of 2 foot...

Keith

Good thought's Bryanna maybe one day someone will find something...but the physical laws are something thats hard to change...LOL!!

Eddy currents are very stubborn!!Like things theyre way...

Keith

How about VLF combined with Ultrasonic. Ultrasound can give a relative sense of density.

Just an idea

Plus the FCC legally mandates how much transmit power a coil can produce.

Bryanna = Correct