Ground penetrating radar?

[JJames1610]

If anyone has any information about these metal detectors, i would like to hear from you. I mostly want to hear from people who have hands on experience, or have been in the field with people using them. Would like to know what is considered the easiest for two people to use. What brands are there to choose from, who in the USA sells them? Anything i should watch out for and stay away from. Thanks

 

[Mega]

Have been looking at a few from Europe,even the cheapest ones are pretty basic and also still very expensive,at the moment the maths just dont stack up in terms of cost to reward ratio,so going down the route and actually paid for a extra large frame coil for using on a Pulse machine that then should do what i want at the moment.GPR machines can be basically the skies the limit and only worth it if you are totally 100% certain the the finds will exceed the expense and time in mastering use one,which in my mind is out of the normal skill sets of a detectorists.

Next step will be testing the large 6ftx6ft frame mounting over the coming months,or the other option that i am also looking at is the 41'' Concentric coil for my Nexusb MP,once again the maths also have too stack up in my favour,the current Pulse setup should do exactly what i want at a very reasonable price as well.

 

[Tom_in_CA]

What type objects are you looking for ? Individual coins ? Then IMHO: GPR is useless for that. You're better off with a standard machine. The "shape-showing" ability of GPR is AT BEST pixel sizes of 1" across. Hence all the objects we find (nails, tabs, coins, rings, foil wads, etc...) are all ....... doh ... 1 pixel ! Hence you have gained no useful information.

Or if it's large caches you're after, I don't think GPR will benefit you there either. You don't get some sort of magical TV screen like picture of jar or box or whatever. Instead, you just get a "messy blotch of pixels". And the depth would be no better than a typical 2-box machine (like a TM 80.

 

[Mega]

@Tom_in_CA,totally agree with everything that you have mentioned,twin box i still reckon would be the best way forward,i use a Fisher TW-5 which will hit large targets in clrar ground deep.forget about small individual coins or artifacts,with a twin box the bigger the item the deeper it basically goes,but its more of a site specific use machine for going in for the kill on say a hoard or other large artifacts.

 

[Wayfarer]

I work with GPR at our office to do archeological research, and Tom is completely right. If anything, he paints a rosy picture. Ours is good for about 3” pixels. Our machine is on e of the less expensive ones at about $14,000. It’s great for identifying old foundations, tracing large underground pipes, or finding old cemeteries, but is useless for what we treasure hunters do. Maybe someday, but that day is far off.

 

[JJames1610]

Not looking for individual coins, cache type hoard. I would expect it to be of a stagecoach strongbox type container. Never dug one up so couldn't say the size.

 

[Wayfarer]

For a large strongbox type target, a GPR still wouldn’t be the best choice. Ours is very large and heavy and is mounted in what is like a big push lawnmower chassis. It’s very slow too with lots of computer analysis of the data. Id recommend a Whites TM 808 or similar for what you are looking to do. You can just walk along over any terrain and it will sound off immediately to any large deep metal object or cache.

 

[Mega]

For a large strongbox type target, a GPR still wouldn’t be the best choice. Ours is very large and heavy and is mounted in what is like a big push lawnmower chassis. It’s very slow too with lots of computer analysis of the data. Id recommend a Whites TM 808 or similar for what you are looking to do. You can just walk along over any terrain and it will sound off immediately to any large deep metal object or cache.

Yep,totally agree with you,i did own a 808 but for the last 5 years have been using the Fisher TW-5 which basically are the same type of setups,they dont get used very often,but its the right tool for the job in hand,if anything that is as big as a safe that has been mentioned then that will certainly nail the target that is if of course a safe is in the ground in the 1st place.

The earlier TM800 was possibly a better machine than the 808,but a twin box in a situation like that would be the right machine for the job.

 

[Mega]

Out of interest what detector setup have you been using or had you previously been thinking about using for this type of hunt ?? and have you all ready detected the area that you surmise it could be located,as a strong box container should be relatively easy too locate i would have thought due to the size of the thing.

 

[vlad]

and which antennae to use.....hi freq, or low? (high freq has better definition but less depth)
Interpreting the data is where you find the devil.........what's real, whats a reflection, or area once dug?
Tom is spot on about images. I agree with Mega on a 2-box---but would opt for a TM-808 ground cancel from Whites.
I'd look at a Deepstar PI with big loop--or some similar (think Deeptech makes one.)

 

[Tom_in_CA]

I work with GPR at our office to do archeological research, and Tom is completely right. If anything, he paints a rosy picture. Ours is good for about 3” pixels. Our machine is on e of the less expensive ones at about $14,000. It’s great for identifying old foundations, tracing large underground pipes, or finding old cemeteries, but is useless for what we treasure hunters do. Maybe someday, but that day is far off.

Good post. Ever since catchy glitzy advertisements showed up, it's been hard to dispel the notions. The depictions of cool star trek type computer screen images propel the misconception . And it's taken on a life of its own. Typically coming from 3rd world countries , where legends of hoards run amok. And they are all, of necessity "6 meters deep" blah blah . And you're a "poor sap" unless you spend $10's of k's on sophisticated crap. (A TM 808 on ebay for $300 is ... of necessity, not going to work).

People there hear these campfire stories, see the glitzy color ad depictions, and think they are going to buy a machine that shows them a magical TV-quality image of a jar, a statue, a box with hinges, or whatever.

 

[REVIER]

On one of the Hoover Boys vids they were at some historical site on a huge farm and in one out of the way area in some woods there was a headstone of a civil war soldier.
Supposedly his body was found in a creek close to that spot long after a battle and he was buried right there...but nobody knew for sure.
They brought in a GPR unit and scanned the grave and did find bones so that was pretty cool.

For the application you are asking about I agree with the others...a two box unit would just make much more sense.

 

[Tom_in_CA]

Sure. I'm not saying there's not certain applications. For example bottle diggers can discern outhouse pits, just by disturbed soil shafts. Or something like what you're talking about.

But for jars with metal, boxes of metal, etc... A person will get just as much information from the beep of a metal detector (telling him "metal is there"), than a magical image of a bunch of blotchy pixels (telling him "metal is there").

It's not going to show jar shape, or box shape, or tell you what the object is, blah blah blah

 

[Mega]

I personally think it all boils down too the 'cost to reward ratio' and with a GPR unless its a complete lost 'Aztec gold hoard' that you are 100% of find or a possibly story of a 'lost safe' then the twin box or even a decent Pulse like the TDI Pro with a large coil will also do the same job but a fraction of the cost of a GPR.

 

[Tom_in_CA]

.... even a decent Pulse like the TDI Pro with a large coil will.....

The problem with using any coin machine (especially a sensitive squirrelly beast like a TDI) is that they will not only do great depth on cache sized objects, but they will "ring the bells of notre dame" on everything else as well. Anything that can pick up coin sized items is going to mean that you'll spend forever-&-a-day trying to differentiate between large and small. Oh sure, you might THINK you'll just set your mind to mentally reject all smaller stuff/beeps. Right ? But no, it never works out like that. You'll spend all your time digging a bunch "just to be sure". And will perpetually have doubts if the little beep your hearing might not just be a big item that happens to be quite deep. See ?

Contrast to a 2-box machine which simply doesn't even see anything smaller than a soda can. Presto: The perfect discriminator for individual coins, nails, tabs, foil, etc.....

 

[JJames1610]

I have tried many detectors from just about all the makers of detectors. Including whites, Garrett, xp deus, deeptech vista, fishers, a lot just trust me. To go as deep as i need to go, you have to hunt in all metal, no discrimination, and cranked up. Its the only way to get deep enough on a larger target, i know because i have test targets from 1 to almost 4 feet deep. Problem is when you do set them up this way they pick up every mineral and iron rock around. When you start to add enough discrimination to fix that problem, your depth just went also. Very frustrating. I had a Garrett 2500 with a eagle eye depth multiplier. I got a good signal sounded just like a metal target. Dug a hole about 4 feet across and 3 feet deep. NOTHING THERE. Took a long time to figure out it was picking up mud. The dirt went from dry to very wet under the soil. It sounded just like a metal target. If you doubt this try it yourself. In the summer when its dry start your machine up and start running it on dry land, then head to the edge of a pond where you can see the difference between dry soil and muddy. Go across it and see what happens, a good signal.
Trying to figure out if someone knows a detector that will ingnore ground minerals, hoping someone could come up with some serious suggestions. I appreciate everyone's input, thanks.

 

[Tom_in_CA]

....
Trying to figure out if someone knows a detector that will ingnore ground minerals, hoping someone could come up with some serious suggestions. I appreciate everyone's input, thanks.

Don't take this wrong, but if you got a false signal from "wet ground" (and dug multiple cubic feet to figure this out), then me thinks "ground minerals" are the least of your problems. I have used scores of detectors also, for over 40 yrs. now. And regarding the Garrett 2-box set up you were using when you got the false wet-ground signal: While I can't say I've used that exact one, I have had experience with the TM-808. Which would be similar. And while you might get drift and flutters over anomolies (wet ground or whatever), you should have been able to tell the difference between THAT and a true target.

So I think you are mis-interpretting something in the audio, or are in some way not using it right. Without being there, I can't diagnose the particular issue. But just saying, that soil going from dry to wet will not cause a signal that the user can not discern via experience, audio, etc.....

 

[MI-AuAg]

Question for you Tom. (or anyone else with any thoughts on the subject)

I've never had occasion to use a two-box machine, but, I've always had interest in what's out there.

One thing that's puzzled me about the TM 808, and Gemini 3. Both are utilized for the same purpose, yet employ vastly different frequencies. The TM 808 around 6 or 7 KHz, and the Gemini 3, way up there around 80 KHz if I am remembering correctly.
What are your thoughts about the huge difference in frequencies used between these two, for essentially the same purpose?

 

[Tom_in_CA]

dunno. I've always thought all 2-box detectors (since the earliest fishers) were essentially the same. Dunno anything about "frequencies" of them, and so forth.

2-box detectors are sort of in a camp all by themselves when it comes to measuring detector ability. Because NORMALLY a "measure of ability" (when it comes to detectors ) is sensitivity. Right ? But ironically, when it comes to 2-box detectors , you DON'T want a machine that is "more sensitive". So for example, if you hold a domino sized metal object *just right* for the TM 808, you can indeed pick it up. (although it's designed only for large-objects-at-depth). Well gee, if you start to make the TM 808 more sensitive to GO DEEPER, then ... gee, what if that starts to make is sensitive enough to ring loudly on domino sized objects, or even smaller ? IT BEGINS TO DEFEAT THE PURPOSE .

But anyhow, getting back to your original question: I dunno

 

[MI-AuAg]

After asking the question, I was thinking, in the yrs. since I was looking at some two-box specs out of curiosity, perhaps the frequencies held in the cobwebs of my memory were off. I checked the numbers, gladly senility hasn't set in, YET. The TM 808 is 6.59 KHz, and the Gemini 3 is listed at 81.92 KHz. I think that's why it stuck in my mind, the huge difference.

I guess the mystery remains? Thanks for the reply!