Vallon VMH3CS Mine Detector

[waltr]

What is interesting with those graphs is the larger, single layer foil has the shortest TC.
As the foil is folded and thickness increases the TC increases.

A guess is that the TC of the single layer foil is just too short to be detected.

[KingJL]

Saw your post and quickly tried a 7in coil that I had previously made for the Vallon using a Whites shell. One inch square foil detected at 2.5" with two LEDs lit. I'm surprised the stock coil did not detect it at all. Will test again tomorrow.

Eric.

Eric,
I tried the 1" single layer foil with my 10 1/4"... could not detect. Switched to my probe and could detect at 2" (2 LED's).

[KingJL]

Eric,
I tried the 1" single layer foil with my 10 1/4"... could not detect. Switched to my probe and could detect at 2" (2 LED's).

Some more tweaking and I can detect 1" square at 1 3/4" - 1 7/8" with 10 1/4 in coil. My test environment is plagued with EMI. positioning for minimum interference and reducing gain to 8 LED's, I was able to detect while moving across target. But stopping even for a second the response ceased. This is inline with other findings that I have noticed... the Vallon is most sensitive to an increasing target signal. I also noticed this behavior when modeling the Vallon integrator.

[MTammet]

Some more tweaking and I can detect 1" square at 1 3/4" - 1 7/8" with 10 1/4 in coil. My test environment is plagued with EMI. positioning for minimum interference and reducing gain to 8 LED's, I was able to detect while moving across target. But stopping even for a second the response ceased. This is inline with other findings that I have noticed... the Vallon is most sensitive to an increasing target signal. I also noticed this behavior when modeling the Vallon integrator.

Made test with 10 inch (26 cm) coil. No response in my case. Have you analysed Vallon damping circuit? What are the best inductance windows for search coils? I think there are certain windows where damping is more effective.

Mihkel

[KingJL]

Made test with 10 inch (26 cm) coil. No response in my case. Have you analysed Vallon damping circuit? What are the best inductance windows for search coils? I think there are certain windows where damping is more effective.

Mihkel

See post 1479 ( http://www.geotech1.com/forums/showt...688#post244688 )

[MTammet]

See post 1479 ( www.geotech1.com/forums/showthread.php?23169-Vallon-VMH3CS-Mine-Detector&p=244688#post244688 )

Sorry, found no answer for my question. I have coils 0.8 mH; 1.14 mH, 1.26 mH, 1.36 mH; 1.56 mH they all work with my Vallon. Only one 1.26 mH refuses to work with one of my Vallons made in 2008 it works with Vallons made 2009 and 2010. Thank you anyway I will make my measurements according to the schematic and TP-s you provided.

[Ferric Toes]

Vallon Coil Tests

Sorry, found no answer for my question. I have coils 0.8 mH; 1.14 mH, 1.26 mH, 1.36 mH; 1.56 mH they all work with my Vallon. Only one 1.26 mH refuses to work with one of my Vallons made in 2008 it works with Vallons made 2009 and 2010. Thank you anyway I will make my measurements according to the schematic and TP-s you provided.

I decided to test the various coils I have made for the Vallon to see what the spread in resistance, inductance, and resonant frequency is. Coils tested were (1) the stock 6 x 10 inch truncated elliptical that comes with the Vallon. (2) 15 inch, (3) 12 inch, (4) 7 inch, (5) 9 x 4.5 elliptical and (6) the ferrite cored probe.

Resistance ohms------- Inductance mH------- Resonant f kHz.

(1) 3.5------------------- 1.473------------------162.06--------- Full length Vallon cable to electronics input.

(2) 3.9------------------- 1.506------------------207.66---------RG58 coax.

(3) 3.4------------------- 1.455------------------183.49---------RG58

(4) 3.2------------------- 1.512------------------174.45---------RG58

(5) 3.7------------------- 1.435------------------173.97---------RG58 with orange polyurethane outer. (underwater version).

(6) 4.2------------------- 1.798------------------179.36---------RG58

The Vallon coil (1) has the lowest resonant frequency and I wonder how important this is. Also, it is the only coil that uses Scotch 24 wire mesh as a shield, as seen in a cross section from a broken coil, whereas all of mine use woven copper, or nickel plated copper, fabric tape. The Vallon also has a long length of coiled thin coax which would add to the capacitance.
The probe (6) inductance is rather high and it only worked with the addition of 1 ohm in series with the winding. Very stable and low noise pickup as a result.

The new mystery is that the Vallon coil will not detect a 1" square of kitchen foil anywhere, but my 12" coil does. No great range, but a definite 1" on the coil axis and also signals positive adjacent to the coil edge. It is a true mono and not wound as a dual field as the shell might suggest.

Eric.

[green]

I decided to test the various coils I have made for the Vallon to see what the spread in resistance, inductance, and resonant frequency is. Coils tested were (1) the stock 6 x 10 inch truncated elliptical that comes with the Vallon. (2) 15 inch, (3) 12 inch, (4) 7 inch, (5) 9 x 4.5 elliptical and (6) the ferrite cored probe.

Resistance ohms------- Inductance mH------- Resonant f kHz.

(1) 3.5------------------- 1.473------------------162.06--------- Full length Vallon cable to electronics input.

(2) 3.9------------------- 1.506------------------207.66---------RG58 coax.

(3) 3.4------------------- 1.455------------------183.49---------RG58

(4) 3.2------------------- 1.512------------------174.45---------RG58

(5) 3.7------------------- 1.435------------------173.97---------RG58 with orange polyurethane outer. (underwater version).

(6) 4.2------------------- 1.798------------------179.36---------RG58

The Vallon coil (1) has the lowest resonant frequency and I wonder how important this is. Also, it is the only coil that uses Scotch 24 wire mesh as a shield, as seen in a cross section from a broken coil, whereas all of mine use woven copper, or nickel plated copper, fabric tape. The Vallon also has a long length of coiled thin coax which would add to the capacitance.
The probe (6) inductance is rather high and it only worked with the addition of 1 ohm in series with the winding. Very stable and low noise pickup as a result.

The new mystery is that the Vallon coil will not detect a 1" square of kitchen foil anywhere, but my 12" coil does. No great range, but a definite 1" on the coil axis and also signals positive adjacent to the coil edge. It is a true mono and not wound as a dual field as the shell might suggest.

Eric.

[ATTACH]44707[/ATTACH]

(1) calculates 750 ohm Rd, (3) calculates 839 ohm Rd. (pi*L*F res) KingJL schematic reply#1749 has Rd at 800 ohms. Would that difference be enough to cause (1) to not detect the foil?

[KingJL]

(1) calculates 750 ohm Rd, (3) calculates 839 ohm Rd. (pi*L*F res) KingJL schematic reply#1749 has Rd at 800 ohms. Would that difference be enough to cause (1) to not detect the foil?

Actually it is 820... look on the bottom side of the damp MOSFETs.

[KingJL]

"... and also signals positive adjacent to the coil edge...

Eric."

I noticed this same effect on my 10 1/4".

[KingJL]

I decided to test the various coils I have made for the Vallon to see what the spread in resistance, inductance, and resonant frequency is. Coils tested were (1) the stock 6 x 10 inch truncated elliptical that comes with the Vallon. (2) 15 inch, (3) 12 inch, (4) 7 inch, (5) 9 x 4.5 elliptical and (6) the ferrite cored probe.

Resistance ohms------- Inductance mH------- Resonant f kHz.

(1) 3.5------------------- 1.473------------------162.06--------- Full length Vallon cable to electronics input.

(2) 3.9------------------- 1.506------------------207.66---------RG58 coax.

(3) 3.4------------------- 1.455------------------183.49---------RG58

(4) 3.2------------------- 1.512------------------174.45---------RG58

(5) 3.7------------------- 1.435------------------173.97---------RG58 with orange polyurethane outer. (underwater version).

(6) 4.2------------------- 1.798------------------179.36---------RG58

The Vallon coil (1) has the lowest resonant frequency and I wonder how important this is. Also, it is the only coil that uses Scotch 24 wire mesh as a shield, as seen in a cross section from a broken coil, whereas all of mine use woven copper, or nickel plated copper, fabric tape. The Vallon also has a long length of coiled thin coax which would add to the capacitance.
The probe (6) inductance is rather high and it only worked with the addition of 1 ohm in series with the winding. Very stable and low noise pickup as a result.

The new mystery is that the Vallon coil will not detect a 1" square of kitchen foil anywhere, but my 12" coil does. No great range, but a definite 1" on the coil axis and also signals positive adjacent to the coil edge. It is a true mono and not wound as a dual field as the shell might suggest.

Eric.

The specs on my 10 1/4" search coil are: 4.1 ohm, 1.495 mH, 241 kHz resonant freq (including coax), 1 meter Belden 9221 mini coax (75 ohm coax).

[Ferric Toes]

Regarding the Vallon coil, in my view the construction is not the best. The tinned copper mesh screen appears to be helically wound directly on the coil bundle without any insulating wrapping material. If there is, then it is very thin. On a few Vallon coils, I have noticed that the detector sounds off if the coil is twisted. This indicates that the mesh tightens up and its conductivity is therefore increased so that it gives a detectable eddy current response. I presume that there is a gap in the mesh to prevent the shorted turn effect.

A quick test with the 7" coil and a 3" x 1" piece of mesh demonstrated that it gives no signal when loose, but when pulled tight gives a strong signal, particularly at the coil edge over the winding. Because of this borderline conductivity at short delays, it might have some additional damping effect on the TX switch off waveform. Could this result in the non-detection of the 1" x 1" foil with the Vallon coil?

This situation does not arise with the conductive fabric tape.

Eric

[Qiaozhi]

I suppose one way to resolve the question would be to construct two separate coils that are identical in shape and size to the Vallon coil, but with one wound with tinned copper mesh, and the other with woven copper (or nickel plated copper) fabric tape. If there's a difference, then the shielding material is the issue. If not, then the discrepancy is caused by something else.

[MTammet]

I use helical wound 5mm copper tape with conducting adhesive and soldered wire lead. No overlapping.

Measurements:

5x6 rectangular teflon 7/0.22 1.14 mH added 1ohm resistor at connector 3.6 ohm supper quiet rg58
4 inch round enameled 0.4 0.8 mH added 1ohmresistor to get 3 ohm noisy, but works rg58
10 1/2 inch round teflon 7/0.22 1.26 mH 3.3 ohm rg58
12 inch rectangular 7/0.22 1.56 3.6 ohm rg58
15 inch round 7/0.22 1.36 3.3 ohm rg58

Measurements without factory cable in Vallon. I use original Vallon. 2008 Vallon will work with all custom coils. 2009 I have will not work with 10 inch and 15 inch.

[jarrett]

Good Evening all,
I have recently purchased a Vallon dated 2010 with the obligatory broken armrest and are in the process of converting a pair of ear defenders to headphones using a pair of piezo sounders but am not sure what type to get be it active or passive or how to wire them either series or paralell and wondered if anyone knew, i found that the audio plug from British military radio series called Larkspur is the same orientation as used on the Vallon so may be available to our Canadian/Australian members, as well as UK, i did note commercial plugs are available but being a cheapskate took this route although i did have a plug knocking about