Gold Signal Response from your detector

My understanding has been the coils field enters the ground and excites the particles in the gold and ground material and when the detector switches from transmit to receive there is a break long enough for the field to dissipate in the ground minerals but enough energy is left in gold that the detector then amplifies on the receive and that is the signal which is heard.
I would think if this is the case the mass of the gold would be the only influencing factor in regard to the signal size in relation to depth but the orientation and exposed surface area of a nugget has proven to be a major factor in the signal generated which to my way of thinking is more of a reflective type or radar response.
How many times are small gold signal responses lost whilst digging a target and then when you shift the target in the dirt heap which improves the surface area to the coil it's, once again easily heard.
I know this topic has been covered before but in the field the answer does not add up to my way of thinking.

ie- Gold being the best conductor for electrons to pass through would mean less lag of electrons in relation to other metals such as steel yet gold produces a better signal in relation to size ?

Cheers Mark

Very easy Mark.

The sum of the squares of the lengths of the legs of a right triangle is equal to the square of the length of the hypotenuse eg: a2 + b2 = c2

actually I understand it as much as I understand the crap I wrote above. I do get curious as to the how's and why's sometimes but then I have another drink and figure I'll leave that to the boofheads on POZ or the geniouses at Minelab and just going back to not caring as long as they know what they are doing and my damn machine works

all I know is I wave my coil over the ground and if I'm lucky enough to wave it over a target it goes "woohoo". I dig it up and if it's gold I then go "WOOHOO!"

Hi Tuna
Yes I guess I asked for that and true to a point who cares as long as we find gold, but I am interested in the whats, whys and how the differing signals gold makes and after digging many targets including gold of all shapes and sizes in varying ground types, I am now at a point of listening carefully to the odd sounds my machine makes in the hope of pulling gold that others have missed.
The days of walking across virgin ground especially in SA and Vic are coming to a end ,especially on known public areas and a better understanding of how your machine responds means more gold.
The last 12 months for me has produced well and I can say I'm not doing more work but understanding more what my machine it telling me.
Mark

actually Mark...I'm looking forward to some replies as I would like to know myself, though in laymans terms I can understand.

Curious though, I hired a 4500 a week ago and I found it was chalk and cheese compared with my 4500 even when running the exact same coils.
This thing was so much sweeter to use even down to the tones when running the exact same settings

Hi Guys, This is not gonna help much but interesting even laughable or just plain bull dust!! ,
as stated the field from the coil energizes the target and this is how we get a response, well I only heard a whisper a few weeks ago while having a beer and not to say there is any truth to this but this is what was stated, someone may of heard of this as well.

An experiment was being undertaken by a couple of blokes who used a generator to electrically charge the ground energizing any targets in the ground, they say that there was a big difference in response once this had been done. makes sense I guess but I'm not gonna be lugging a generator around in a whell barrow as well.

I think those blokes may have started drinking a lot earlier than you

Harp

Have you already had a beer or two? I could not help to crack myself at your comment! You really do have a sense of humor.

Keep it up. (That is your humor, of course!)

Best

Kudu

Guys the bottom line is eddy currents induced in the target.Not taking into account all the variables in the goldfields,there is a simple formula called flemings right hand rule.In simple terms it says you need 3 things to produce electrical current in the target,movement,a magnetic field and a conductor(gold hopefully).Once current flows in the target a 2nd magnetic field will be produced.This then produces an eddy current in the receive coil(same coil on a mono) to produce the tiny voltage sensed by the detector.
Eddy currents flows best in good conductors ie:gold,silver,aluminium etc which explains the good response on detectors.The magnetic field must cross the conductor by 90 degrees to get max current in the conductor.Im guessing here that a large surface area or cross sectional area will give the best induced current and not neccessarily the mass.
This is my best guess from engineering studies so I hope it helps.

Hi All,
Just a quick warning, DON"T USE A GENERATOR TO ENERGISE the ground it will probably KILL You,
A guy in Bendigo died earlier this year next to his generator while was trying to get worms.
Cheers Mark.

Interesting point kingfish
I agree creating an electrical field in close proximity to any conductor will induce a flow of electrons from within and as in our case the metalic target but the field generated would be stronger at 90deg . but in practice an example of a piece of wire laying flat on the ground will generate a stronger signal than if it was stuck in the ground pointing up to the coil ?
Another thought if the machine is only sensing the left over electrical energy left in the target after a period of delay the unit would be able to sence this energy with a stationary coil to target which we know does not happen , tape a metal object to the coil and nothing is heard ?
If the target is reflecting energy back to the coil and there is movement of either target or coil then there would be a warp or variation in the field and to me this makes more sence in what the unit is monitoring to create a target response .
Mark

[quote="MS"]
How many times are small gold signal responses lost whilst digging a target and then when you shift the target in the dirt heap which improves the surface area to the coil it's, once again easily heard.
I know this topic has been covered before but in the field the answer does not add up to my way of thinking.



Gday Ms


The 'halo" effect around the nugget while buried and undisturbed seems to make the nugget appear larger than it is to the coil I think, when you disturb the nugget by digging it it shift the position of the nugget and breaks up the "halo" so maybe the coil does not detect it as well.

Apart from that if the nugget is flattish and it gets turned on its end the surface area is smaller and limits the response by the coil, sometimes I wonder if this is why from time to time you will find a small nugget in an old dig hole, the original finder has given it a bit of a dig and shifted it, then you may come along from a different direction and ping it, the size of the coil is also a factor too I suspect.

I did this myself one time and messed about with digging a small piece, as it was hot and I got frustrated I left it and pushed a biggish rock over it thinking I would come back later and get it then, anyway I forgot about it and had to leave early, so after I left a so called mate went over it and dug it out, 3 grammer, but flat and skinny, didnt tell me about it for some time, he watched me messing with it and after I went he sleezed back over and got it out, must have needed it more than me.


cheers



stayyerAU

One thing to remember with PI detectors is the on time for each pulse is very short only about 4% of the duty cycle.During a sweep of the coil it would be very easy to miss a target on its side.If we had a hundred pulses per second and say the coil moves at 1 meter per second each pulse would occur every 10mm.Hence the need for a number of sweeps to get an accurate signal on small targets.
Another thought on the halo effect is it possible that over time some metal leaches around the target into the surrounding compacted ground especially ferrous metal or metals that oxidise.This may result in a target appearing larger until disturbed.
Found a very informative link on metal detector theory that may interest some:
http://www.thomasathomas.com/Metal_detectors_work.htm

[quote="Adrian SS"]
[size=12]The different decay rates for the ground matrix and precious metals are known values so by changing the time that the receiver waits before switching on enables the PI detector to ignore certain ground mineral conditions while still responding to precious metals.


G day Adrian and thanks.
So given the above why can't we ignore everything except gold?

Brett

G/day fisherman,
be great wouldn't it, maybe one day it will happen.
Trouble is part of the decaying fields from the ground and other metals occupies the same territory as that from the gold and other metals, or in other words there is still some of the ground signals remaining when the gold signal is being sampled. Salt and iron mineralisation is relatively easy to ignore with a PI detector but metallic iron and other metals are a major problem to "iron out" so to speak for a gold only PI metal detector.

I think hand held PI detectors like the Infinium,TDI and the ML detectors have done a pretty good job given the current technology.

Another thing to realise about PI detectors is that unlike VLF machines that respond to anything that alters the shape and electrical balance of the transmitted field, the PI responds only to the magnetic fields generated by the eddy current flow in the target material, you can alter the shape of the PI transmitted field until the cows come home and you won't get a signal response unless the object causing the shape change has eddy currents flowing in it that produce a strong enough magnetic field to create a signal in the PI receive coil

Adrian

Thanks Adrian for an easy to understand answer.
I'm guessing the varying size, shape, density and depth of nuggets don't help the cause either.

Brett

Yes Adrian, thanks from me too. A good post Brett.
Jigalong

I agree very good post replys Adrian ss and Kingfish ,that has given me something to think about, I think it's important to get a sound understanding on how things work that way you can intemperate and get a better understanding in what you machine is telling you which hopefully can lead to more gold.
I guess in todays world most people don't care much how something works as long as it does, but I'm a bit more old school and like to pull things apart and see what makes them tick.
Cheers Mark

yep some beaut replies thanks!
Mark I used to be the same, pull it apart to see how it works, until I realised once back together they usually never worked properly again
Now I'm not so much concerned with how it works, but more how to work it

Thanks for the feedback chaps.

Cheers,
Adrian SS

Need some help with this one people.....After receiving a strong signal i have proceeded to uncover something which i did not think was AU as the signal appeared to sharp a response, after excavating down to about a foot deep the signal was not in the hole so i proceeded to check the dirt that had come out of the hole.....the signal had become very soft and only just audible, so i pass handfuls of dirt over the coil till nothing is left .....no signal???? level off the dirt and wave the coil over the hole and there the signal is again strong and loud....so i go thru the process of digging out the hole again, passing the soil over the coil and nothing again couple of expletives .....level the ground out pass the coil over it.....the signal is back again only this time i tell it to jam it and walk away with it marked on the GPS for future reference.

Any ideas??? this the 3rd time this has happened

Were you in Tracking mode ?
Detector might have been balancing out mineralised soil and playing games with you.

You are probably being introduced to reactive clays or clay domes. They are indeed a menace. A red colour is usually a dead giveaway. The signal can mimic a target all too well. If you are unsure, ground balance over the material you have dug out. If the signal is diminished or has gone from the hole, there's your answer.
The other options are that the target is so small as to become bl**dy hard to find or you have shot it out of the hole with your pick. I have done this several times so now, if I lose a signal, I automatically scan the surrounding area.
Hope this helps

Hi U308,
I have come across exactly the same sort of ground you are talking about, i found a small quartz blow on top of laterite ground and recieved a good signal and proceeded to dig and dig and dig trying to isolate this signal.

The ground was lateritic and the bigger pieces were exactly round 6-8mm diameter and like you, had to leave the signal, i went back to it a few months later and dug some more but still couldn't isolate the signal.i eventually left, still not satisfied what it was all about, the only thing i didn't do was to pan the stuff i dug out as it could be fine gold.

I wonder if it is one of JP's "annomulous " grounds.

Regards Ron

Hi U308,
I'd side with Robert on the "clay dome" explanation. They are a real menace at times and seem to be especially prevalent after good rains. I've dug them to 18" deep chasing what I thought was a deep target. If you leave the hole open for a few hours and let it dry out you'll find the signal is gone or vastly diminished, AND then you fill the hole in of course. The 4500 likes them even in Enhance timings, especially the green coloured clays I find. RD and I dug an 18" hole a few weeks ago beside a large tree for one of these menaces.

I find that digging on one of these doesn't seem to lower the response like hot ground does, and it doesn't lessen either.
If we suspect we have one of these we lower a slightly smaller coil into the bottom of the hole. Moving the coil slowly from side to side in the hole should make the detector scream if there is a metallic target present. If the response is small or zero, then fill it in. Cheers.

Thanks fellas....Appears this may indeed be the explanation as 2 of the signals were in a reddish brown clay and the other signal was in laterite.
The signal in the laterite was the type that never got any louder as the hole got deeper, i ended up giving it away as it was a tough gig towards the end 15 minutes for 1 inch.... don't mind finding AU but it is recreation not a job.

The signal in the clay was more of a sharp response rising quickly before dropping off....whereas AU seems to have a slower response as in (woo hoo)

Anyway cheers fellas

So much to learn so little time

Hi U308, I think your experience is very common. In similiar circumstances I usually dig out a reasonable little heap of the ground (digging a narrow hole and getting dirt from down a bit) I usually balance very thoroughly on top of the dig out dirt and the signal in the hole usually becomes so subdued i can walk away.

But sometimes the deep signal response is still there. Sweeping the coil the same as i did before i balanced I usually find the signal will now appear stronger on the edge of the hole, the target centre has definitely moved!!!. I use this as an indicator of hot ground and walk away. ( but i make sure i centre the signal well at the start)

I done a balance over the signal (the hole) and found the signal then goes away. I walk away. (I have dug many of them to be sure and they were not metal targets. The ones that were gold or iron i was not able to balance out the signal to any huge degree (but hot ground signals do disappear) . I realize many people would say i balanced out a possible good target and would tell me i am mad.

The biggest issue i have is on the odd occassoion with a good sized coil where the signal has a solidness about it and is really deep. You must hook in and dig out a heap of dirt before you can confirm (with a bigger coil) if it is a hot ground target or a metal signal. Don't make the mistake of walking away from huge deep nugget.

Tributer