Vallon VMH3CS Mine Detector

[kingswood]

Hi Kingswood,
I used to correspond with Chris Hake who did a lot of nugget hunting on the salt lakes near Kalgoorlie. I built some special rectangular coils for him, which he mounted on a towable trolley. I seem to remember he used a SD2200 at the time and the combination worked fine. I would guess that the Vallon will work fine, but would benefit from the firmware upgrade so that you could slow the response down a bit, particularly when using bigger coils.

Unfortunately, Chris Hake, a very enthusiastic prospector with a great sense of humour, died a few year back.

Eric.

Thanks Eric. Shame about Chris
Yes there is still gold in lakes here....
I am waiting another week or 2 for the permit then its all systems go!! I have the old SD2000 with a choice of salt coils and DD's so have options if the Vallon doesnt like the mineralization! From what I have heard, my GPZ7000 will likely struggle due to the high salt content.
Will be very keen to see how the Vallon handles it!!

[kingswood]

Hi Kingswood,
I would guess that the Vallon will work fine, but would benefit from the firmware upgrade so that you could slow the response down a bit.
Eric.

Thats an interesting idea I know people doing mods on ML detectors (such as the SD and GP series) add in extra stuff that allows for timing changes...I wonder if thats possible on the Vallon?....I dont know enough about electrical engineering

[kingswood]

I have done so much reading over the last couple of days that my eyes are sore !!!
You guys are way to smart for me!....I wish I had done an electrical engineering degree instead of an MBBS!!
To elaborate on my post above:
Some blokes (like Woody, Ishmael and Barry Johnson) did/do mods on the ML PI detectors that add a variable pulse frequency control, variable gain and a timing change switch. I dont understand the Vallon schematic so I dont even know if that would even be possible.
Has anyone ran simulations (using that neat computer program!) to see if its possible??
Hopefully someone way smarter than me can help
After deciding to try some salt lake detecting, my interest in the Vallon has been aroused again!

[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.

[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]

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]

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, 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.

[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]

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

[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.

[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

[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.

[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]

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: