A question on signals

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If one is using the same size coil, same kind of coil [DD], or for that matter mono, and the same brand coil on a 2100, 2200 3000, 3500 or 4000 ML, is there any difference in the size, [depth + width] of the signal, per detecter.

If so than I would think that it would account for why the signal from one detecter may cover just a bit more area and a bit more depth in the parallel sweep of the search pattern, over that of another detecter using the same coil.

Has anyone ever heard or read any comparison data on this??

Bob T.

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BOB, camparing the 2200sd and 3500, both with the Platypus coil . I would say that there is more tweeks on the 3500 to make the signal heard more easely. And a different tone. The 2200 was very poor with volume, even though I was running the same amp on both machines, I think the 3500 has a little edge over the 2200sd with the same coil. If I ever get my 2200 back from touring around the USA I will make a better comparison. Grubstake

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I know that detecting is a lot about the operator. Also the 3500 has a lot of tweeks that some of the others do not have. But the Volume, Tone, Audio ect. are only variants of the Threshold and should not change the electromagnetic field, or signal from the coil.

To clarify the question a bit.

A hypothetical example: For the sake of argument, say we use a 14" CT, mono coil.

An electromagnetic field is generated in the coil and a cone shaped signal is sent out.

Lets say we have this coil on a 2200 and the cone shaped signal is 36" deep and at ground level the cone is 12" in diameter, at 18" or midway to the bottom it is 8" in diameter.

Now if we put this coil on any of the other detector's mentioned, are the all of the detectors going to generate the same configuration of equal size or will some be of smaller or larger size. In other words, if we put the coil on a 3500 or a 4000, will we then generate a cone, maybe 38" deep, with a 14" diameter at ground level and 10" in diameter at the midway point?

Correct me if I'm wrong, but I believe that the detector is just the Transmitter and Receiver with many variants and the coil is the signal generator. Therefore the cone size should be the same in all detectors, unless, some units supply more power to the coil than other's, there by increasing the size and strength of the signal. :unsure:

Bob T.

Hey Flak,

I'm with you. I would also like to see three or four detectors, say 4000's, using the same coil.

Take one machine and get over a target at the extreme max. depth, to where you had a very, very faint signal, and then test the rest with the same coil on the same target.

It may well be a brow raiser. But then who knows. :huh::unsure:

Bob T.

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You really brought up a great observation here.

Yes, there are two very important 'ends' to a detector, throw one aside be it the coil or the source of power and your doing nothing more than "swingin' in the breeze". :unsure:

I must go back a few years here to explain my thoughts on this.

First lets say I've got a flying machine that will pin-point objects in the sky. The two parts used to do this are.....the 'power/electronics source' (Tx) and the 'antenna' (Rx) coupled to it. Since the 'marriage' of both accomplished the end means of a required task, no one did to much to improve performance either way until forced to do so!

Now lets say that someone changes or revises the power supply, in this flying machine, and its tuning/matching characteristics to only serve the 'original antenna' or coil.....Sooooo, how does the new power configuration react in responce to the same 'antenna/coil'? Well...

Here's my point, depending on the source power and adjustments available the 'antenna/coil' can be tuned to its maximum effect depending on what your searching for at any on time or, it can "mute" a target as well!


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Colorado Bob

I have never seen anything like that to compare units using the same coil.

I did a lot of research and reading and seen some comparisons with coin shooter machines but none with all the Minelabs.

My thoughts are that coils give off the same general pattern. They are man made so they may have some minor differances. The signal strenghts are differences as you see on folks increasing the voltage of their battery systems that can give more punch goinging maybe a little deeper and wider.

The signal processing has nothing to do with the coils except that it receives a change in the transmit and the receive signals strenght. This then is processsed and send you a specific pattern of sound to the headsets.

I can only see that the more expensive ML's have more advance processors that can identify more quicker and more accurately then older versions.

Disclaimer. I may be 100% full of it in my statement above.

But it is my idea of how it all comes down to finding gold.

Grub stake had it right 25% detector 75% operator.

I like the non techincal way Dennis tells me " LOW AND SLOW"


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In my test garden at home I have 5 sizes of lead that I smashed flat but still rounded, and all about 2 feet apart, and each of those 5 sizes I have 6 different depths all about 18 inches apart. Like columns of targets in the ground. Deepest are about 12 inches and shallow is about 3 inches. It's been in the ground about 5 years. What I have found on all detectors, -including my 2200 minelab- is that on the marginal signals it just depends. Sometimes a deep small target will be really loud and clear and obvious and then I'm swinging the coil and going back to it and that same deep, small target won't give much of a signal at all, real weak like ground noise. Maybe ground balancing out the target, but other times I'm not sure if that is what is going on cause with the minelab I'm in all metal mode and not tracking. Sometimes the deep, repeatable signal is only good for a couple of swings and then it goes away or gets unreliable. On the shallow targets this does not happen, its bing, bing, bing.. So when I am detecting and I get a good signal just for a couple of swings, and I am in a good area I will dig and figure out what it is. Sometimes it's not right in the center where I thought it was, it is on the side of the hole, and small, or rusty iron will do it too but once the ground gets disturbed the signal goes away. Remember when you were a kid and tried to ride somebody elses bicycle and the way it handled was so wierd, I think detectors are like that.

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Hi All,

This is an interesting thread and has a lot of valuable info plus it answers some interesting questions. Unfortunately, it also asks more questions. Now, for starters, the statement about low and slow should be viewed with open eyes. You might want to read what was posted on the Minelab Mods forum about going too slow.

Here is the link:


If the link doesn't work, here is what was stated;

"Another important variable in testing is sweep speed, particularly with DD coils. As Pi’s usually use some form of low pass filtering sweep speed can affect both sensitivity and depth. On the ML platform very slow sweep speeds may result in significant depth losses (up to 22%) and this is coil size, type, target and ground dependant. As well the settings that are used on the machine also affect the results as some settings on the Gp appear to slow down the integrators? (which helps reduce noise by averaging it out) but reduces depth and sensitivity. Other settings change the†mesh size†of the sampling windows or gate them (amplitude gates) so that some targets start to slip through or are rejected"

Now, what isn't stated in the above quote is detectors generally use bandpass filters which consist of a low pass and a high pass filter. Go too slow and the high pass filter reduces the sensitivity. Now, go too fast, and the low pass filter will reduce the sensitivity also. The trick is to find the ideal speed and stick with it.

So, techniques can become more complicated, especially if one realizes things change when you change settings on the detector.

Acronn pointed out something that is very true, detection of marginal targets can change from day to day. Even sweep direction will make a difference. This makes it even more difficult to compare coils.

As for comparison of power into the ground on the different ML's, I doubt one would be able to readily measure any difference if you were to compare each transmit signal even though the voltages were changed with the GP series. Now, what you can't see is just how the signals are processed and that has changed also from detector to detector and that can make a big difference.

To make matters worse, the processing is changed when you change detector settings. So, things change again, and depth capabilities and comparisons will change along with it.

In other words, it isn't as simple as saying one should use "this" setting or "that" setting and call it good. One really needs to get to know their detector very well to know what is the best settings for the location they are hunting.

I don't recommend a test of one to determine much. If you do, you will make others who follow you happy.

The guys over at Prospecting in OZ pointed out some quirks on the GP 4000, including the "hole" in the detection of a particular nugget. What wasn't determined is just how many holes there are and at what size of gold and at what detector settings. What else wasn't noted is the fact that most likely, all the other models have "holes" also and they depend upon the settings of the detector. I know the SD 2100 did on the one I tested.

Now, before anyone gets their dander up, this condition basically is true of all PI detectors using the common technique of dual sampling to determine and adjust the ground balance.

The bottom line isn't that one should defend or condemn what is happening or all the quirks that are pointed out, but rather to recognize that they do exist and know when they happen or might happen. Also, know what has to be done to circumvent the quirks. In most cases, it can be done. The trick is knowing how and why.



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Thanx Reg great thread, I've been following along on the thread you mentioned, talk about getting some controversy started but you are very correct about settings changes and how the parameters differ, probably the most significant change in the Minelabs now is the use of the Gain control which actually gives the operator a chance make real adjustments..I can remember talking to Jack Gifford one time and he pretty much blew the theory about cone shaped signals, he said they were actually more towards a balloon shape..Didn't make much difference to me as everytime I get something that interupts the threshold I tend to scratch some of the surface away and turn to check the signal from another direction, I've worn out a lot of RH shoe sides too. Can't believe how many Deep coins I found over in Hawaii this last month using this method again, saw a few other Detectorists hunting but watching their tecniques made me think these hunters were missing those faint interuptions. Found some nice jewelery Using my PI Pro and Excal....... :) HH...Geo

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Reg. I would say that swing speed is one of the things that seperate the men from the boys with a PI detector . I can make a weak but good signal either get stronger or weaker just by changing sweep speeds depending on the detector settings. Maybe even more important is a smooth controlled swing at a consistant height. I've had the opportunity to watch hundreds of people detect and can pick out the ones that will go on to find lots of gold , and the ones who probably won't ever find much unless they get really lucky with a big one or two. Some people just cannot get a smooth swing going no matter how hard they try. Wild ,erratic , inconsistant movement is a sure road to failure with a PI . False signals increase dramatically and weak targets aren't heard. The opposite can be true for a VLF operator. Some of the best with a GM3 or GB2 are a blur as they work around obstructions and cover a lot of ground in a short time. These guys really struggle when switching to a PI and some can never make the switch succesfully.

There is also another factor which most people don't consider and that is not even discussed and that is matching swing speed to forward progression. Many don't realize that they swing in a rythym with their steps. It is natural and more comfortable to the back and arm to have the coil to in a certain position as the weight passes from one foot to the other. As the forward progression picks up , the the swing speed unconsciously does also. Motion is motion whether side to side or forward . Even if the side to side swing speed remained the same when one doubles his forward progress , the effect is to increase the swing speed. The GPX4000 has the capability to adjust for this in several ways, but unfortunately many people will never make the connection. There are some things that can't be taught to some people. Some folks can learn because of a natural or learned understanding of the technical aspects of PIs. Some folks who have no understanding of the technical side have a natural ability to pick up on the language of the detector. None of us are created equal in all aspects. With the wide variety of settings now available, the guy who cannot force himself to swing slower or walk slower might have better luck with the faster swing speed settings. The tools are now there on the GPX4000, and I suspect on the Goldscan also.----Bob

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