Some beginner questions about "two-box" metal detectors...

[Punchy71]

Hi,

1)What are "two-box" metal detectors designed to be used for?
2)How do they differ from a regular, standard VLF detector with an extra large search coil on it?
3)What are some pro's and con's to using them over a regular VLF detector?
4)Do they use the same basic technology as a VLF detector and the same frequencies?

Thanks

 

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[JrMack]

I use a Discovery 900-TF 2-box detector and will try and answer you're questions. The 900 is a predassor to the whites 808, some would say a better unit.

1)they are used for locating pipe lines in ground and any big objects at great depths, ie. compact car at 20 ft. but I pick up items like a horseshoe or even as small as a door hinge. It depends how you set it up. It can also tell if the ground has been dug up and filled in ie. mineralization
2)2-boxes have a receive antenna and a transmit antenna or coil--mine is about 16"X8" for each made of aluminum. these are carried parallel to the ground
3) they can cover a lot of ground quickly and not effected by really small targets,, manual ground balanced and are hard to determine deph within 6-12' in my experience
4) 900th is 12.5khz basic circuitry
Hope I have helped you out, checkout youtube for some videos of the 808 and good hunting

 

[Tom_in_CA]

JR-mack does a good job on your Q's. I would add:

1) 2 box detectors are designed for larger objects at depth. Eg.: Soda can to jar sized objects, and bigger.

2) Well, from a PRACTICAL standpoint: A standard machine with a large coil will admittedly probably get the jar, or toaster-oven sized object JUST AS DEEP as a 2-box machine. HOWEVER, the advantage of the 2-box machine is that you will NOT be able to detect smaller objects at all. Like individual coins, nails, tabs, foil, etc.... So the 2-box machine becomes the "perfect discriminator" to avoid all such pesky objects, if your quest was only for larger objects. Contrast to a standard coin machine: While, yes, it might go just as deep, yet you'll be perpetually digging small junk. And even if you set your mind to "only dig big signals", yet you'll be perpetually digging a bunch "just to be sure". Hence despite that each type could accomplish cache hunting, yet there's a practical benefit to the 2-box, over the standard type detector, for this purpose.

3) Addressed in answer # 2

4) Dunno about this one.

 

[signal_line]

Several years ago, the two-box were called Industrial detectors. No mention of cache hunting. Whenever you put a big coil on a VLF it is going to have problems with mineralization. Not much use if it can't find a one-gallon can at three feet. Not only not much use, worse than nothing at all because you think you checked the area. Pulse Induction has a much better chance of hitting deep targets in mineralized soil. I had an 808 and it does pick up small stuff like barbed wire.

 

[Tom_in_CA]

....Pulse Induction has a much better chance of hitting deep targets in mineralized soil....

Sure. But the devil is in the details: Heaven help the poor fellow who goes to try to use a pulse detector, for cache hunting, @ any ghost-townsy ruins type site. He will go psycho when the "bells of notre dame" ring on every nail, staple, pushpin, etc...

.... I had an 808 and it does pick up small stuff like barbed wire.

barb wire ? Maybe big hunks of it. But not smaller strands, eh ?

The smallest object I could get an 808 to hit on, was about a domino or silver-dollar sized object. And only then-so if finely tuned, and held close to the ground. So since we were hunting cookie-jar sized objects in a very junky farm yard, we deliberately held the 808 higher, and ignored teensy flutters.

 

[Carl-NC]

To answer #4: "maybe." The Discovery TF900 was a ground-balanced VLF but also had a basic TR mode. The last variant of the TM808 is basically a stripped-down 6000 circuit and is VLF-GEB only. The Fisher Gemini is, I believe, a basic amplitude-type TR design.

Of the 3, if you want to hunt for Mason jars full of coins then the TM808 is your better bet, mostly because you can buy one. If you want to survey-map ground nuances, then the TF900 (in TR mode) plus a data logger is what you want, but the TF900 is a scarce item. If you want to trace lines & pipes, the the Gemini is the best choice.

I have all three, and the only one I use is the Gemini for tracing wires & pipes. If I wanted to hunt caches, I'd probably use a PI with a 1 meter coil. And I'd probably have to build it.

 

[against the wind]

I used the M-scope for tracing plumbing services to houses and structures in NYC. You clamp the transmitter box to the water service at the inside wall of the property. Then you walk with the receiver box outside the property to trace your water service line back to the water main. The same can be done with your sewer service. In the event of a clay sewer pipe, you would run an electric sewer snake into the line and then clamp the transmitter box to the steel sewer cleaning cable. If the clay pipe has collapsed, the sewer snake head will usually stop at the point of collapse. That is where you would dig to make the repair. Used correctly, these machines are very accurate.

 

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[h=2]Interesting thread.\\ Seen this on craigslist

Over 100 pipe locators and metal detectors - $2500 (New Brunswick, NJ) hide this posting[/h][FONT=&quot]

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163 Livingston Ave.
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Have a huge inventory of used 2 box pipe locators / pipe tracers and Whites and Garrett 70s/80s high performance metal detectors. May work and have no time to test.Lots of coils! Will throw in a hoard of about 1000 Metal Detector/Treasure hunting magazines. First $2500 takes all. Bring a truck to carry away. Call first.

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