Vallon VMH3CS Mine Detector

[Ferric Toes]

Wondering if someone with a Vallon could try an experiment. Detection distance for a 1inchX1inch piece of regular strength aluminum foil and a 1inchX1inch piece of regular strength aluminum foil folded twice for .5inchX.5inchX4layers.

Hi Green,
I tried your test, with the following results. Foil used was 0.02mm thick. An accurate 1inch square was cut and this was undetectable by the VMH3CS with the stock coil and standard settings in Normal mode. However, when folded twice and held tightly together it was detectable at 2.5inches under the coil. This figure did not change when switched to the mineralised mode (ground cancelling) which was previously balanced on a piece of Australian ironstone. If folded twice more to give 1/4inch square, the Vallon will now detect it at 3inches in Normal and GB mode.

Eric.

[green]

Wondering if someone with a Vallon could try an experiment. Detection distance for a 1inchX1inch piece of regular strength aluminum foil and a 1inchX1inch piece of regular strength aluminum foil folded twice for .5inchX.5inchX4layers.

[MTammet]

I use the same cable. Use lead wire under shielding and have good soldered connections.

[ionut_mtb]

This is cable error. What rg 58 you used. Use with tinned copper shielding RG58 CU. I had same problem with cheap RG58. It seems Vallon is very sensitive on cable. Use at least 1.5m cable with resistance (with cable ) at least 3 ohm. In my case it worked. I think it is somehow related to damping adjustment in Vallon firmware. There are only certain regions where damping can be adjusted. If your coil is out. Meaning too over or under damped Vallon gives this error.

I will do more experiments. I use good cable, tinned:

[MTammet]

This is cable error. What rg 58 you used. Use with tinned copper shielding RG58 CU. I had same problem with cheap RG58. It seems Vallon is very sensitive on cable. Use at least 1.5m cable with resistance (with cable ) at least 3 ohm. In my case it worked. I think it is somehow related to damping adjustment in Vallon firmware. There are only certain regions where damping can be adjusted. If your coil is out. Meaning too over or under damped Vallon gives this error.

[ionut_mtb]

Made 60cm coil (25”) 0.5copper wire, before shielding with fabric nickel tape i had it tested. With 2metter of rg 58 vallon give error. Without the cable(leads directly into the vallon connector) it works. What shoud i do? I did not check resonant freq. i’m afraid that if i complete the coil, will be to late for adjustments/moddifications.

[Clemente]

I wish I had, but I am working on it. I suspect that a lot of broken coils with their lower shafts have been scrapped as they come as one unit. I am trying to source some, as the lower shaft is essential for making other coil sizes which I could do myself. Without a lower shaft you have the problem of the connector and the male coupling piece to somehow make. If I can get some shafts, then there is the possibility of making 12in and 15in coils, plus probes. Unfortunately, I doubt that any aftermarket PI coils will work because of the unusual high inductance/resistance that is required for the detector to work.

Eric.

Hi Eric, PM sent

[Clemente]

I have spent the last couple of months doing an in depth analysis of the VHM3CS electronics. Eric Foster graciously made available an electronics unit for study. The unit displayed the dreaded LED error sequence 2&3 5&7 10&11 13&14, which I have repaired. I have kept Eric apprised of discoveries as they have occurred. This effort was not to reverse engineer the VMH3CS, but rather to gain an understanding as to it’s performance.

WhenI started this, I had assumed a complicated and sophisticatedtransmitter and simple analog pre-amp with digital sampling andprocessing of the receive functions. I also assumed that the reasonfor demonstrated performance on small resistive (fast tau) targetswas due to very early ADC sampling of the received signal. I couldnot have been more wrong… on all points! Most every day ofdiscovery brought with it another surprise.


Ihave since come to appreciate the VHM3CS as an eloquentimplementation of hybrid analog and digital processing. It utilizesthe appropriate application of 3 technologies... analog, digitalFPGA, and DSP processor. The transmit function is much more simplethan I had presumed and the analog processing of the receiver muchmore sophisticated than I had presumed. All timing signals aregenerated by the FPGA and are therefore ultra stable and precise. The DSP processor makes all determinations of the timing parametersthat are supplied to the FPGA as well as DSP receiver post processingand filtering.

Twoareas that truly impressed me are the efficiency and effectiveness ofthe pulse transformer MOSFET driver circuit and the sensitivity andperformance of the integrator circuits. I have documented myfindings/determinations in the following document.

Theattached “what we know” paper documents what I have discovered. The attached TX-RX (top)test points.pdf depicts the various testpoint that were amassed during this study. I present these to theforum to further discussion and discovery. Again, Eric Foster cannotbe thanked enough... as none of this could have been accomplishedwithout his gracious contribution of an electronics unit for study.

Letthe discovery begin… You do not necessarily need an ultra fast coilto detect small resistive targets!!!

Thanks for sharing.

[MTammet]

Recently I was searching on a wet uncultivated grassland with high grass and uneven turf. In 2012 detectorist reported one find. Viking sword hilt from 800+900 AD Archaeologists asked me to get a loo at that site. They used ML Sovereign and found one more hilt when detecting 5 years ago. So I decided to help them and took my Vallon with factory coil. Archaeologists had to reopen the case because more than 70 sword fragments with pommels guards ect were found with Vallon. All items were 25+40 cm in soil plus 15 cm grass and unevenness. When tested sword pommel was heard 60 cm in ground.

Mihkel

[Ferric Toes]

Yes, but you have mostly all kind of nails and some big iron in old settelments. Horisontal nails have very distinctive signature and also spike wire and they tend to give very strong signal. I pick only small signals because coins are small. I also pick some rusty iron pices. You just cant do nothing about that.

Many years ago I got permission to search a Roman villa site in Oxfordshire after the archaeologists had finished with it. Using a PI metal detector was very difficult because the site was littered with tiny Roman sandal nails. However, I persevered and eventually got a larger signal that I investigated. It turned out to be a very nice iron Roman door key, which made the day worthwhile.

Eric.

[MTammet]

Yes, but you have mostly all kind of nails and some big iron in old settelments. Horisontal nails have very distinctive signature and also spike wire and they tend to give very strong signal. I pick only small signals because coins are small. I also pick some rusty iron pices. You just cant do nothing about that.

[ionut_mtb]

How can you use vallon in old settlements? You have alot of iron there, many signals. I know vlf can’t go deep in mineralization like pottery, bricks, so pi is the best.

[MTammet]

Yes, i drilled it out the same way whith 25mm drill bit and sanded threads a bit. The only thing in my opinion which matters is resistance and capacitance and resonant frequency. I made one tiny 4 inch coil with 0.9 mH and it works too. It takes time for Vallon to check it but then it calms down. Large coil I made 1.5 mH.

[ionut_mtb]

You can also make a smaller coil for a bit better sensitivity on small gold. I have small rectangular(a bi for less sensitive to ground aed thatnd emi) 4,5x6 inches. Made from teflon 7/0.2 wire. I can detect flat gold nugget 0.3 gram from 3 inches in mineralized mode at 7. It is not much but for larger it goes deeper. But you can not get much more from changing coil size. Small silver coins 0.2 gram are detected at 6 inches. 3cm bronze round buckle brooch at 13 inches. It works good and quiet on wet sand and salt water. Coils are temperature sensitive so you have to accomodate them with environment about 2 -5 minutes. Ferrite rode Eric made is probably best for small gold. I do not know how it handles hot ground though. I left inductance at 1.15 mH it works ok so far. I think that even better than with fatory 1.5 mH. Better to use dielectric putty. I use glass fiber polyester. Dielectric material works the same way to RF as optical glass works for light. It helps a bit with emi in my opinion. We have experienced that when dealing with wind energy parks and radar technology. I am not an expert on PI detectors, but have some experience on radar technology. In my opinion factory coil is not the best choice for that detector. one thing I dislike is that signal will not increase gradually from small item to a bit large and ect. when you raise coil slowly. It tends to jump and scream. Whith the small coil I made it works ok.

how does your vallon not going into alarm for not using 1.5mH?

Thank you for your usefull posts. I managed to find a coupling for water hose with same tread as vallon connector. on the inside i had to trimm like 1-2mm to fitt.

[MTammet]

You can also make a smaller coil for a bit better sensitivity on small gold. I have small rectangular(a bi for less sensitive to ground aed thatnd emi) 4,5x6 inches. Made from teflon 7/0.2 wire. I can detect flat gold nugget 0.3 gram from 3 inches in mineralized mode at 7. It is not much but for larger it goes deeper. But you can not get much more from changing coil size. Small silver coins 0.2 gram are detected at 6 inches. 3cm bronze round buckle brooch at 13 inches. It works good and quiet on wet sand and salt water. Coils are temperature sensitive so you have to accomodate them with environment about 2 -5 minutes. Ferrite rode Eric made is probably best for small gold. I do not know how it handles hot ground though. I left inductance at 1.15 mH it works ok so far. I think that even better than with fatory 1.5 mH. Better to use dielectric putty. I use glass fiber polyester. Dielectric material works the same way to RF as optical glass works for light. It helps a bit with emi in my opinion. We have experienced that when dealing with wind energy parks and radar technology. I am not an expert on PI detectors, but have some experience on radar technology. In my opinion factory coil is not the best choice for that detector. one thing I dislike is that signal will not increase gradually from small item to a bit large and ect. when you raise coil slowly. It tends to jump and scream. Whith the small coil I made it works ok.