Depth Meter for a tf-900

[tesoro dog]

Hello All! I need help, so I asked myself,,, Who are the Smatest guys on T-Net Hmmm,,, then it came to me, of course the Tech guys !!

Hopefully some of you fellow Hunters can give me an idea, how to work this,,, what I need is a very inexpensive way to jerry rig a depth meter to a TF-900 Two Box Deep Seeker. I don't need to I.D. my target, just to find the depth before I start digging. By certain signs, I am figuring the target is about 9 or 10 ft. deep and it is buried in a desert wash, with very little mineralization in the sand. I have read that the Arc-Geo has an attachment that plugs into the earphone jack of the tf900, but I need to get the price down a lot! HA!

If you guys can help, you will forever be in my Prayers! PS. If this question has already been answered,, Please direct me to the thread. Thanks Amigos!!! td

 

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[EE THr]

I have never used that particular detector, but there are a few ways of approximating depth of a target, on a machine which has no depth indicator.

With an ordinary detector, you can simply raise the coil, until the signal fades out when scanning over the target. If you know the depth range of that detector, just look at the distance the coil is above ground when the signal faded out, and the remaining range will be the depth of the target. Although the air will have a slightly different response than the soil, this usually gives some idea, but you would need to know the approximate target size. And at over 5 feet deep or so, this wouldn't be easy!

Another way is to angle the coil at 45 degrees or so, and scan from the side. Then do this from the other side, and triangulate the position of the target below ground. Accuracy might vary. I haven't done this a lot with regular detectors, and I don't recall exactly how well it went. Actually the best way would be to keep the detector in one spot and twist the angle of it, rather than hold it at a certain angle and walk backwards---because increasing the distance to the target will also diminish the strength of it, whereas just changing the angle of it would minimize that effect.

Another way would be to reduce the sensivity to an exact point on the dial, but you would need to know what the maximum depth is at that point, by experimenting. Of course, the size of the target would also affect this method. This way would be less accurate to the extent that the size of the target is not known. For example, if the target indicates it has a shape of 3 ft. by 2 ft., you would figure it was certainly larger than a beer can, but if the same target were really deep, it might only indicate as one small pinpoint, depending on the shape of the field created by your coil configurations. But if it's a large target, that deep, then the first method suggested should also work, where the signal fades when raising the coil(s). But that still won't tell you if it's a large target, but very deep---or a small target, not so deep.

The depth problem is the same for detectors with detph indicators, though, because they go by signal strength, which is what the first and third methods above would use. Most regular detectors assume the target to be the size of a coin. Garretts makes one which apparently computes the time that the signal strength holds at a high value as you swing the coil over the target (and thus calculates the size of the target); against the target signal strength value itself, and comes up with what should be a more accurate depth indication. A coil swing of a certain speed is required for this to work best. I haven't used that one, either, though, so I don't know exactly how well it works, but it sounds interesting.

Someone else may have some better ways to suggest.

 

[JohninNC]

EE THr is right on track. A VLF machine uses signal strength to determine the distance. You could simulate this by taking a one gallon paint bucket full of brass and using it as your test bed. You would set up your detector at max distance it will detect the bucket, making sure there is nothing close by to interfere. Next you have to get a meter, probably a volt meter would work, and you have to connect it to the input of the receive coil on the box. Use a meter to measure the range of the voltage when the object is at max detectable distance and when it is at minimum detectable distance. For example the voltage may go from 0 to 2 volts. You would need to add a trim pot of say about 10k ohms in parallel with the meter and apply 2 volts while you adjust the trim pot to make this the max reading on you volt meter. Now when you connect your volt meter to the input of the receive coil it will measure the minimum and maximum detection distance. Now all you have to do is run your test with the gallon paint bucket full of brass an mark the increments on the volt meter for min and max depth. The only variable will be the difference in the size of the object detected with the bucket. But it will give you a pretty close range. Hope this helps.