mcjtom

Hello, I’m not sure where to post it: would anybody know a good documentary on metal detecting/treasure hunting (technology, applications, history) of interest to upper high school students? Cheers!

I found this white paper from Minelab that discusses the ground balance technicalities: https://www.minelab.com/__files/f/11043/KBA_METAL_DETECTOR_BASICS_&_THEORY.pdf

Also a somewhat related question: am I right to assume that pressing All Metal button opens up all the discrimination notches but doesn’t change the current recovery speed (it inherits the recovery speed from the mode the detector was on before engaging the All Metal button)?

Thank you! Out of curiosity, if a single or multi frequency machine has a GB adjustment, what does it actually do to the return signal (as compared to filtering low phase shift signals by notching them out)?

Upon further reading, the matter seems a little more complicated than I thought...

With the detector such as the Vanquish 440, which performs auto ground balance (or Noise Cancel - I imagine trying to reduce the Ground noise and the EMI somehow combined) on startup and is multifrequency - does it make sense to either pump or swing the coil during the startup or keep it 'stationary' near the ground as the manual instructs?

I started thinking about buying Minelab Vanquish 440. The closest distributor from Bangkok (according to the Minelab website) is in Kuala Lumpur - that's a different country. It looks like it is possible bo buy this detector in Thailand from online sellers - but I really don't know who they are. Is that a good idea to use the online sellers? If not, how do I do that from Thailand?

Metal detectors often seem to have a 'Depth Gauge'. How is it calculated? Is it the strength (or inverse of it) of the amplitude of the return signal? So, for instance, everything else being equal, the 'deep' target would mean either a stronger target at greater depth or a weaker shallow target?

Hi, my detector came with the manual as well (same as on the picture). I was just looking for more technical information on it in my first post. Interestingly, I paid an equivalent of about 50 NZD for it in Thailand. I'm already learning from it and from all the kind comments by more experienced members - so it was a worthy investment for that alone. p.s. This correlation of swing speed and ID values (the ID values for a surface conductive target clearly and consistently increasing with sweep speed, not necessarily getting more variable) doesn't let me sleep at night - is that unique to the Mental Detector? Even so, why would the phase shift (which I imagine the IDs use) increase with the faster swings?

Thank you! While I think I understand the idea that consistent, overlapping swings with the coil at constant height, parallel to the ground would produce more stable IDs, I can’t figure out why the ID values increase with higher swing speeds and decrease with slower ones, reproducibly, with the same easy test target, everything else being equal (or close to it)?

I wonder what is the physics behind my Mental Detector showing higher VDI (larger phase shifts I gather) for the same conductive target when the sweep speed is higher?

Hello, Many thanks to all! I went out to see what this "Mental Detector" does, trying to learn. I took 4 modern baht coins, of different sizes made from different alloys: 2008 (RAMA IX) / 2018 (RAMA X) VDI 1 Baht - Nickel-plated steel (3g/20mm) 0 2 Baht - Aluminum bronze (4g/21.75mm) 20-30 5 Baht - Nickel-plated Copper (6g/24mm) 70-80 10 Baht - Cupronickel / Aluminum Bronze (8.5g/26mm) 19-25 I put the coins on the surface of what I thought was a relatively clean area. The 'thing' does, at the very least, detects metals and seems to discriminate between them the way that makes some sense to me given the alloys. An unexpected (at least to me) finding was that the VDI was correlated with the speed of the sweep - faster sweeps consistently corresponded to higher numbers (the scale is from 0 to 100). Why would that be, I wonder? I imagine that those ranges of VDI for the same and easy targets like coins on the surface are fairly wide by the standards of other detectors. Is that correct? Would better single frequency detectors be able to narrow down those ranges? I also imagine that multi-frequency detectors would be even better at discrimination? Many thanks again! EDIT: I mixed up the VDI in the original table - now it should be what I've seen.

Many thanks for help. It came with basic manual, I was just looking for some more information or experiences to calibrate my expectations. It was relatively easy to buy in Thailand, based on description it wasn’t that different from similar models, and while I already found some metal detecting specialty shops selling famous brands, they are obviously much more expensive and I don’t know how to choose yet. Cheers!

Hello, I'm a total newbie. I bought an inexpensive detector called Quick Shooter MD3030. It came from China to Thailand and it also doubles as 'Mental Detector' judging from the picture below. I think I understand more or less by now what it does - there is a sensitivity and selectivity (including notching out in 6 phase shift ranges) target identification value display plus 3 tones audio for different ID ranges. It operates on single frequency of some 6 kHz and seems to have round coils. There is also 'depth indicator' on the display, which I imagine would be the return signal/target strength (or the inverse of it)? I'm not sure if I understand how VLF detectors know the depth of the target. Would anybody be vaguely or intimately familiar with this detector and are there is any technical info or reviews, beyond what I know that I can consult to learn more about it? I don't even know who the manufacturer is... A related question: since this detector doesn't have a background threshold control, would decreasing sensitivity play a similar function? I know that this particular model may not be up to the Board Members' standards but please help the newbie. Many thanks!