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TWO METAL DETECTORS
Does anybody have information on using two metal detectors like a LRL. From what I have heard, two detectors are modified. On is placed on the ground and the other one is used to detect the signal the same way the rods due in a LRL. The difference is that the receiving detector makes a sound and is used to trace the signal ine to the target. This was told to me by an old timer who could not find the instruction on how to modify the detectors. Thanks!
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Wish this would work, BUT???
CoilMan, I think your friend could have mistaken an old/OLD Two Box detector for this configuration, or may have misunderstood a discription of a Twin Probe Earth Resistivity Meter setup for Imaging under ground.
I read another post in the "I Think" GeoPhysics forum about a 4 probe setup with high Freq/Current That isn't EXactly the Standard form of ER survey but a varation of such. I haven't tried this method but I have read about in the 60's where the same technique was tried to precharge the metal targets in the ground with an eddy current hoping to gain Depth.
Sincerely
Bill Adams -
Coilman,
If you've ever been in a competition hunt, then you probably know that two detectors operating at the same frequency will interfere with each other. So, if you have two such detectors, turn one on, lay it on the ground with the coil flat to the ground, and set it for max. transmit power.
Take the other detector, run it in all-metal mode, and see what you pick up. In my own experiments (years ago) using two White's analog detectors, I could get interference at 10's of feet away. Some radials were stronger than others, likely because of variation in ground conductivity, and this can give the illusion of "signal lines" that might be misconstrued as being caused by a buried target. Not so. In my experiments, my buried test targets produced zero effect on the radiated interference signal, and were only detected when my search unit was right over them, just like normal.
Some years ago, Ralph Shull of NJ was advertising a "long range locator" based exactly on this premise. It did not work, of course, and Mr. Shull is now deceased. Other people have proposed (and sold) various schemes that involve transmitting signals and then detecting a "signal line" to a buried target, usually by means of dowsing rods. But this "signal line" only exists in their imagination. If it were otherwise, some very simple tests would prove it out, and we would see products from every major manufacturer utilyzing this method.
- CarlComment
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Carl I see what you mean...BUT.....
My friend uses and XLT and I use the old Eagle Spectrum, when we get around 15 feet apart, the machines both give a SIGNIFICANT increase in depth. Any closer and they interfere, and further and no result.
I think there must be something in this idea, or are they performing like a two box machine?Comment
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Hi Sean,
I have the Gemini 3 two-box made by Fisher. There is one transmitter and one receiver that make up the two-box combination. If you place the transmitter over a buried pipe or large wire, you can trace the route of the buried object with the receiver. You can also accomplish other tasks with the two-box, such as a deep seeking metal detector.
Therefore, to answer your question…No, when running two metal detectors in a close proximity is not performing like a two-box.
Hope this helps, JimComment
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Two Box or Mutual Inductance???
Sean, I can see where your two machines could ADD when in Proximity to each other.
Det.1 is emitting a Freq. ??? which induces a eddy current in a Target ???.
Det.2 is doing the same on the target.
We all know that MOST Circuits DONOT produce Perfect Sign waves.
And we know that Square Waves are made up of ??? fundamentals and Harmonics.
Additionaly we know that most filter circuits opperate within + or - ??? MHzs, KHzs by a few or more ???Hzs of the Optimumn the Designer set the Center Freq for.
So, If one machine is Radiating a +or- Freq around a Center Freq and the next machine is receiving at a higher or lower freq that will overlap on the plus or minus ENDS of the first freq then I don't see why that Sean's OBSERVED Apparant increase in depth wouldn't be possible. You would be ADDING some portion of each machine's Harmonic Freq to the other.
Sorry, folks if the Above isn't Clear, I haven't had to use my EET training since 1989, so am VERY rusty on the Termanology and Theroy.
Hope Some of you Other, More up to Date, EET techs can either Flesh out the above or SHOOT it down or Steer it in the correct direction.
Sincerly
Bill AdamsComment
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Hi,
This is a very old thread, but I thought I would mention something that might be the device in question. The idea is unique and could be used as a basis for experimenting. Who knows, maybe a new unique design could be built that would detect objects deeper.
Many years ago, before Compass went out of business, I had a conversation with one of their engineers, a John Earl I believe, and he mentioned a device something much like one in the question here.
It was his idea that a very large coil could be built and driven by a high powered transmitter. Now this coil would be very large, possibly 25 to 50 ft in diameter.
A second device would serve as the receiver only and rely on the large coil as the only transmitter. The receiver would be tuned to the frequency of the transmitter.
A person would walk within the large coil while operating the receiver and listening for any radiated signals from metal objects.
I have no idea of such a device was ever tried, but it was discussed.
RegComment
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Hi Again,
Sorry for the second post, but I forgot to log in so I couldn't edit my first post.
Now, what I didn't mention was the large transmit coil would simply be placed on the ground and searching would be done by walking within the coil using the special receiver. The large coil would then be moved and another large area searched.
RegComment
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Well maybe this should be on another thread but how about a different approach?
1. Two pulse induction units using the same coil and never run at the same time.
2. They would be a GP3000(shaft mounted) and the GS5(hipmounted). Both use the same coils.
3. A button on the GP3000 handle which would disengage power to the GP3000 and engage GS5. A Nautilus headphone system.
4. Why? Combine the strengths of each (depth vs metal ID) Woo/Wee respones are going to be different on each to the target. A method of further IDing different metal types. PI nautilus version.
Yep this may be outrageous but I am bored today.
GeorgeComment
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I very much doubt this would work. My first thoughts are that any signal from a buried target would be completely swamped by the transmit signal. In a normal detector coil arrangement the RX and TX coils are arranged so that the residual received signal is very close to zero. With the arrangement you have described, the RX coil is being moved around within the TX coil. The only possibility might be to record the RX signal strength within the TX area, plot the results, and look for any anomalies. Personally, I cannot see that this one will fly.Originally posted by Reg
Comment
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Bruce candy proposed placing a large coil on the ground and working within and slightly outside using a 18" mono (Aus patent 633536).
He says...
"A conventional DD uses coils of the same size. The sensitivity to small target objects of these coils decreases as a 6th power law.......<snip>.
The sensitivity to a small target object of the very large transmit and "normal" sized receive coils decreases as cube power law with distance of the object from the rx coil for distances of the object from the rx coil of the order of the dimension of the receive coil but less than the dimensions of the tx coil.
Such a system has the advantage of being more sensitive to deeply buried objects for the same magnetic field interrrogation strength in the region nearby the receive coil."
Qiaozhi,
There isn't a problem with the the target being flooded by the tx as the sampling is done after the tx has been switched off in pi designs.
Rob.Comment
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OK - I agree, if you are using pulse induction, but no-one has mentioned that until now. So far, BillNEWAST compared this idea to a 2-box detector (which is induction balance), Sean Goddard described a scenario with an XLT and an Eagle Spectrum (both IBs) and Jim talked about a Gemini-3 (an IB 2-box).Originally posted by robby_h
As none of the detector manufacturers offer such a system (as far as I'm aware) I can only assume that it doesn't work very well. Unless (of course) you have a good imagination and can get a good "signal line" to the target.
Comment
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Hi Qiaozhi,
Again, the discussion about this design happened about 1992 or so, so the idea isn't new and I am sure it has been thought of by many engineers in the field.
Now, I am not sure, but I would think it would work even with a VLF design. At least, I do not see any reason it wouldn't
As for why no manufacturer ever built one, I can't say except most companies build detectors aimed at the mass market, which this one isn't. Also, most manufacturers work on a tight budget that leaves little money or room for extended experimentation with dramatically new ideas, especially if the future sales may be very limited.
So, I can see why little or no actual work has been done in this area.
RegComment
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Hi Reg,
Interesting thread.
I have been experimenting with multi coil designs for a number of years with mixed success. Most of my work is based around UXO demining designs and in particular PI. There are a number of designs within this discipline that have attempted to use either a fixed (ground layed) transmit loop in which multi- recieve loop arrays are used to search within or, a large fixed array of both transmit and recieve coils (usually mounted to a vehicle). The transmit coils , sometimes more than 8, are controlled in such a way as to enhance any vector responses from the recieve coils that are produced from the larger UXO targets (against both ground noise and other smaller metal fragments).
Current research worldwide is centered on methods to detect the smaller and more obscene mimimal metal personel mines which litter some parts of the world in very large numbers. The attempt is to use similar methods together with other technologies GPR and chemical ID.
It is a very real prospect, that the same metal detection technology will one day be used within the ranks of hobby and gold detectors.
Cheers
Brian KComment
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