Vallon VMH3CS Mine Detector

[kingswood]

Great work Eric.
I will be interested to see how the small coil goes.

[Dai]

Looking good there Eric, I am looking forward to the postman in the next few days to arrive with mine. Will then have to find some time to go out and play and experiment..being a full time dad can be interesting at times! Also noted is the leadwork..not often seen but should be mandatory with decking near or above damp course, good job there.
I have sent you a PM regarding arm supports if you have any available, Im not sure what or how you get a notification of message so have mentioned this here.
Looking forward to more nuggets of information and knowledge..and hopefully a wee little manual of hidden info on these machines.

[Ferric Toes]

I have been adding to my armoury of coils for the Vallon electronics. I now have one in a 12in shell, which I think would be my preference for beach hunting, and a 5.5in coil squashed into a small elliptical housing. These two latest coils worked first time with no problems, provided I kept the inductance, resistance and resonant freq. with certain limits. The Vallon coils I have range from 1.493mH - 1.512mH with resistances of 4 ohms and 160kHz f(res) with cable. It seems that you can go outside these limits to some degree as my 15in coil reads 1.556mH, 3.7ohms and f(res) 171kHz. That works very well.

The 12in coil was a bit closer with L = 1.493mH, R = 3.3 ohms and 160.3kHz. The 5.5in coil has L = 1.446mH, R = 2.6 ohms and 172kHz. The only worry was the low R, so I added a 1.0 ohm metal oxide resistor in series with the coil to bring it up to 3.6 ohms. Running the electronics on a bench psu set to 4.5V gave 372mA draw current for the 2.6 ohms, compared tp 332mA with the additional 1 ohm, so the resistor was cemented into the end of the coil housing. The latter level of current is similar to the standard Vallon coil at this supply voltage.

To get L close as possible to 1.5mH the 15in coil requires 39 turns; 12in coil 44 turns and 5.5in coil, 70 turns. Spiral wrap on the coil, then copper fabric tape as a shield. Nickel plated copper fabric tape is to be tried on the next coil but connecting the ground wire to it requires a different method as soldering is not possible. A thin drain wire is one possibility as the sample I have has conductive adhesive. The drain wire can be between the tape and the underlying spiral wrap.

The small coil in the elliptical housing can still detect a nickel at 13in and a 18K thin gold ring weighing 3gm at the same range. This coil I plan to use in cluttered areas, such as a field we own behind a watermill. The Mill goes back to the 13th century and a quick run with the standard Vallon gave a lot of signals quite close together.

Eric.

[kingswood]

Better day with the 30cm coil
I used it on one of the other Vallon's and it was able to run at sensitivity 12 without false alarming at all. I found that swinging at about 1m/sec was good. Picked up a metal staple at around 4 inches in a dry creek bed. No gold...yet !!

[kingswood]

Many thanks Funfinder.
We might have to wait until some VMX10's are decomissioned, to run big coils for large deep objects. I doubt that will be for a few years though.

Eric.
http://www.vallon.us/xypics/bilder/vmx10_leaflet_09_2013.pdf

Can't wait
It is interesting that the VMH3CS manual says: "Upon switching ON the detector electronics recognizes which search head has been connected and switches over the pulse control automatically". I guess from this they mean that the pulse rate changes when using the larger (60cm) coil???

[Ferric Toes]

Thanks for the info, Eric. Under such circumstances everything is fine and its a great idea
to built some larger coil (not too large) and to mod it for "civilian" hunting for high mineralized
locations and if discrimination is not that important.

Its a fantastic way for "refurbishing" such kind of detectors or just having a great experimenting time.

If this becomes "fashion" also people at countries with MD-restrictions can create some
much more useful coils concerning depth - your beercan in air test with the not finished coil
is already fantastic and such result never would've been possible with the small standard coil!

Many thanks Funfinder.
We might have to wait until some VMX10's are decomissioned, to run big coils for large deep objects. I doubt that will be for a few years though.

Eric.
http://www.vallon.us/xypics/bilder/vmx10_leaflet_09_2013.pdf

[Funfinder]

Thanks for the info, Eric. Under such circumstances everything is fine and its a great idea
to built some larger coil (not too large) and to mod it for "civilian" hunting for high mineralized
locations and if discrimination is not that important.

Its a fantastic way for "refurbishing" such kind of detectors or just having a great experimenting time.

If this becomes "fashion" also people at countries with MD-restrictions can create some
much more useful coils concerning depth - your beercan in air test with the not finished coil
is already fantastic and such result never would've been possible with the small standard coil!

[kingswood]

I find that it is necessary have to sweep at 1m/sec even with the 15in coil, otherwise the SAT reduces the detection range. Eric.

A few pages back I posted a bit from one of the reports that said there is a large error rate when the larger coil (in that case it was the 60cm) is swung at 0.1m/sec. They said no error when swung at a rate of greater than 0.9m/sec.....I think part of my issue with the 30cm coil has been swinging to slowly!...I was trying to follow the old adage of gold hunters, "Low and slow"....but I am not sure that works with the 30cm coil! Heading out for a bit of a hunt on this lovely Easter Monday, so I will experiment with a faster swing speed. This is difficult for the larger coil as our block has quite a few shrubs and over-burden, but will see how it goes. That is the beautiful thing about the standard coil...I have shoved it right into the middle of shrubs and it copes well !
I located a couple of old dry-blowing heaps on our block, so the larger coil may well work effectively on there....especially after I rake it down a bit ha ha

[Ferric Toes]

Hey Eric, this is a real good setup - congrats - lightweight coil-mover etc. - great, but the coil is still too small.
If this detector is sensitive enough you can work with some 60-70cm coil. Just try it.

Well, this MD is not the newest one but here you might find how it compares:

https://www.minelab.com/__files/f/266333/STEMD%20%28Mozambique%29%20Testing%20and%20Evaluation%20Report%202005.pdf

Personally I wouldn't rely too much on such over 12 year old things - especially if it comes to demining!
You have to know that modern plastic mines (full of x4 etc.) contain VERY SMALL & FEW metal parts.

You can mod such MDs for treasure-hunting (especially at countries where are no other MDs available)
but PLEASE don't use them for demining if your life is precious to you!
There exists meanwhile MUCH better detectors for demining.

Hi Funfinder,
The Vallon detectors that are on the market here in the UK are mostly 2009 - 2010 vintage and are VMH3CS, which is still listed as being in production today. There have been no VMH3's going back to 2005 that I am aware of, as mentioned in the report. The VMH3 has less features than the VMH3CS, the most obvious are the lack of a confidence signal every 2 seconds, no pinpoint button and no facility to change search heads. Possibly, it is also programmed differently.

The ex military units are usually battered, scratched and covered in dust with sometimes a broken armrest, but the internal electronics is remarkably well protected and being built to MIL standards is working perfectly. The technology is right up there with the best today and arguably exceeds most MD's for treasure hunting. It depends what you want to do with it of course. My tests, and by others, show that it is an excellent detector for the beach, right down to the water's edge in fully saturated sand. It also coped very well with iron mineralised ground up to the worst encountered in Western and South Eastern Australia. It has more than adequate sensitivity and detection range to gold rings and nuggets. Today, I air tested a small, thin, 18K ring weighing 3gm which was just detectable at 18.5in. My 18K wedding band weighing 10gm was just detectable at 21in. That of course was with my new 15in coil which is now fully potted and ready to go, and the re-housed electronics.

As far as using even bigger coils, I don't think this this would be the right detector. Vallon do make a 60cm coil for larger ordnance, but I believe the detector VMH3UXO is programmed to have a slower filter than is used for smaller coils. I find that it is necessary have to sweep at 1m/sec even with the 15in coil, otherwise the SAT reduces the detection range.

Nobody would use these decommissioned units for mine detection. It would be foolhardy to do so. The sole interest, and especially from my point of view, was to see how good they would be as a metal detector for hobby and professional use when looking for coins, rings, nuggets, relics etc., as a result of the good performances that have been reported in the demining literature.

Eric.

[kingswood]

Hey Eric, this is a real good setup - congrats - lightweight coil-mover etc. - great, but the coil is still too small.
If this detector is sensitive enough you can work with some 60-70cm coil. Just try it.

Well, this MD is not the newest one but here you might find how it compares:

https://www.minelab.com/__files/f/266333/STEMD%20%28Mozambique%29%20Testing%20and%20Evaluation%20Report%202005.pdf

Personally I wouldn't rely too much on such over 12 year old things - especially if it comes to demining!
You have to know that modern plastic mines (full of x4 etc.) contain VERY SMALL & FEW metal parts.

You can mod such MDs for treasure-hunting (especially at countries where are no other MDs available)
but PLEASE don't use them for demining if your life is precious to you!
There exists meanwhile MUCH better detectors for demining.

I dont think anyone who buys a 7 year old VMH3CS has any intention of using it to find land mines
Personally, I bought a couple to try and use for Gold....The very small and few metal parts that you mention are sometimes aluminium, such as the firing pin in the PMA-2...My theory would be that if the VMH3CS can find a tiny piece of aluminium, it should find gold too.
From lots of reading, including the trial report you linked, I am convinced that the VMH3CS is a very capable detector, that will excel on the beach and also, because of its ability to handle mineralized ground, will do well in the goldfields. My efforts so far in finding gold have not been successful, but the Vallon has done very well in the area I have used it in. I have no doubt that when the Vallon actually swings over a nugget, it is likely to find it

[Funfinder]

Hey Eric, this is a real good setup - congrats - lightweight coil-mover etc. - great, but the coil is still too small.
If this detector is sensitive enough you can work with some 60-70cm coil. Just try it.

Well, this MD is not the newest one but here you might find how it compares:

https://www.minelab.com/__files/f/266333/STEMD%20%28Mozambique%29%20Testing%20and%20Evaluation%20Report%202005.pdf

Personally I wouldn't rely too much on such over 12 year old things - especially if it comes to demining!
You have to know that modern plastic mines (full of x4 etc.) contain VERY SMALL & FEW metal parts.

You can mod such MDs for treasure-hunting (especially at countries where are no other MDs available)
but PLEASE don't use them for demining if your life is precious to you!
There exists meanwhile MUCH better detectors for demining.

[kingswood]

Wow Top work Eric!
That looks brilliant!....Good luck on the beach!

[daverave]

Hi Joe,

That is exactly what I did. With the teflon 7/0.2 wire I overlaid with spiral wrap and on top of that a woven copper screen. With 39 turns I got an inductance of 1.556uH, a resistance of 3.7 ohms and a resonant freq. of 180kHz. The stock Vallon coils average out over 10 units at 1.504 mH, 4 ohms with cable and 160kHz res.freq. With 2m of cable instead of 1.5m on my 15in coil brought the res.freq down to 171kHz. This works great and I don't anticipate any further problems. I will pot the coil over the weekend for field tests next week. I'm not looking forward to the digging I might be doing though.

Picture shows the configuration so far. Whites shaft with long fibreglass coil shaft. Belt mounted electronics with inbuilt step down transformer and filter for standard stereo phones. these are switched to stereo so that phones are series connected to give 60 ohms. Either volume control on phones adjusts both.

Eric.

[ATTACH]39492[/ATTACH]

that looks very impressive indeed.

[Ferric Toes]

Eric,

Try using a PE spiral wrap just with an ID a little smaller than the size of your coil wire bundle. The PE has a low dielectric so it will provide a spacer between the coil wire and the shield to help reduce coil to shield capacitance. If you measure the coil inductance when on the hook coil form the inductance should be a few percent lower than the final inductance when the coil is removed from the coil form, when the PE spiral wrap is added and when the shield is added. This should help you get your next coil closer to the stock coil that you measured. You can even try to put another layer of PE spiral wrap with a larger ID than the first layer, to keep the shield snug against the coil for more stability.

I hope this helps.

Joseph J. Rogowski

Hi Joe,

That is exactly what I did. With the teflon 7/0.2 wire I overlaid with spiral wrap and on top of that a woven copper screen. With 39 turns I got an inductance of 1.556uH, a resistance of 3.7 ohms and a resonant freq. of 180kHz. The stock Vallon coils average out over 10 units at 1.504 mH, 4 ohms with cable and 160kHz res.freq. With 2m of cable instead of 1.5m on my 15in coil brought the res.freq down to 171kHz. This works great and I don't anticipate any further problems. I will pot the coil over the weekend for field tests next week. I'm not looking forward to the digging I might be doing though.

Picture shows the configuration so far. Whites shaft with long fibreglass coil shaft. Belt mounted electronics with inbuilt step down transformer and filter for standard stereo phones. these are switched to stereo so that phones are series connected to give 60 ohms. Either volume control on phones adjusts both.

Eric.

[bbsailor]

Hi Joe,
When the copper fabric shielded coil was working it was giving identical ranges to the subsequent Scotch 24 shielded one. The former one is fine when the room temperature drops to 50C or below. Above that, the Vallon shows a coil fault and won't work. It may be a capacitance change caused by temperature. The resonant frequency is lower than the stock Vallon coil anyway, so maybe the detector senses that. I am now winding a third coil using Teflon insulated 7/0.2 which I hope will push the resonant frequency up to be nearer the stock coil.

Eric.

Eric,

Try using a PE spiral wrap just with an ID a little smaller than the size of your coil wire bundle. The PE has a low dielectric so it will provide a spacer between the coil wire and the shield to help reduce coil to shield capacitance. If you measure the coil inductance when on the hook coil form the inductance should be a few percent lower than the final inductance when the coil is removed from the coil form, when the PE spiral wrap is added and when the shield is added. This should help you get your next coil closer to the stock coil that you measured. You can even try to put another layer of PE spiral wrap with a larger ID than the first layer, to keep the shield snug against the coil for more stability.

I hope this helps.

Joseph J. Rogowski