mono coil discrimination.

[minersright]

Can some body tell me if mono coils can be used as a discriminating coil on a VLF detector??. And a PI detector??

Thanks in advance Minersright.

[Qiaozhi]

Can some body tell me if mono coils can be used as a discriminating coil on a VLF detector??. And a PI detector??

Thanks in advance Minersright.

No they cannot. A "mono" coil is exactly that - one coil. A VLF (induction balance) detector needs two coils. One for transmit and the other for receive.

[Geo]

If you use a PD3200 PI detector then Yes you can use the mono coil as a discrimination coil for PI.

[Max]

Can some body tell me if mono coils can be used as a discriminating coil on a VLF detector??. And a PI detector??

Thanks in advance Minersright.

Hi,

yes is possible. But first you have to define what's a VLF!

It's a definition problem: often we talk about VLF just referring to TR configurations and so what really are "IB machines" using VLF op. frequency.

As stated above by Qiaozhi, you cannot do disc with a single coil in a VLF/TR system... cause one coil is intended to generate transmit (tx) ac field and other(s) as receive coils (rx). But it's obvious... you need at least 2 coils in a TR detector...

If for VLF you just mean "very low frequency" detector you could have:
- a "straight" BFO detector in the VLF freq range and all its versions...
- an Off-resonance type (bfo too, but different approach)
- a VLF/TR system as above, that incidentally would be induction balanced too, and various configurations for that model
- a VLF/TR two-box type for long range
- a variable Q detector with center frequency in VLF range

So... as example assume you have a VLF version that is a BFO or off-resonance-BFO... and you could disc things using inductance variations of a monocoil...
You get the picture ? You can disc even with a monocoil !

Of course you need special circuits... filters etc but it's possible (and also reliable). Examples are e.g. VLF-PLL (bfo), off-resonance (bfo), old-fashioned disc BFO (tru beating ones)... and on var-Q they could disc using same principle for disc and amplitude variations for just detecting in all-metal.

So answer is yes "you could disc even with a monocoil vlf".

About PIs... well there are monocoil machines that could disc stuff... e.g. PulseStarII etc but disc is never "safe" on PI detectors cause time domain analisys is farther complicated respect to e.g. phase shift or frequency shift in the freq. domain (as described above... using PLL or phase comparing networks).

So answer for PIs is "at the end: yo" (yo have to discriminate... digging the hole...).

Best regards,
Max

[Leto]

One coil induction (ballance?) detector

Hi there
There's very interesting project by Andrei Chtchedrine right at geotech site..
http://geotech.thunting.com/pages/me...rei/index.html
any comments?

[Max]

Hi there
There's very interesting project by Andrei Chtchedrine right at geotech site..
http://geotech.thunting.com/pages/me...rei/index.html
any comments?

Hi Leto,
"One coil induction (ballance?) detector "

Don't think there is any induction balance. Just a monocoil...
For sure there is induction! She's always there!

"
For little iron objects both filter output signals will be synchronous: output voltage swings first to minus, then to plus and comes back to zero. For nonferromagnetic metals and large iron objects the response will be different: output voltage of only the first (upper filter in diagram) swings first to minus, and then to plus. At the output of second filter reaction will be opposite: output voltage swings first in plus, and then in minus."

Seems could be ok... but problem is that have low performance on small items:

18cm diameter coil -> coinÆ 25 (mm) - 0,15 (m)

Also Magnum could beat ! Anyway I think is a good project to understand some VLF machines working... expecially old-fashioned.

Best regards,
Max

[Qiaozhi]

My assumption here was that Minersright was asking about an induction balance machine when he stated VLF. Both BFO and off-resonance detectors can be VLF, but nobody uses these nowadays. Their use is relegated to children's toys.

[minersright]

mono coil discrimination

Qiaozhi, your assumption was correct, I was thinking about the newer model vlf detectors, garrett, tesoro, minelab,etc. I should be more specific when asking a question. Thanks to all that replied to my queries.
Regards Minersright.

[Max]

My assumption here was that Minersright was asking about an induction balance machine when he stated VLF. Both BFO and off-resonance detectors can be VLF, but nobody uses these nowadays. Their use is relegated to children's toys.

Hi Qiaozhi,
yes you are right. BFO and off-resonance aren't advanced machines today, of course.
I know just one person that uses (seriously) a good BFO (tru beating one, gives increasing or decreasing tones around 2KHz) and that could identify target using sound from headphone...

Of course, his detector (cannot identify it, think is an old UK made product, he don't remember brand and now is very old)
don't go so deep... but he can disc using ears! That's the interesting point!

He found many good things that way... and tested newer machines too... but remains with his older BFO! He feels good with it.

Best regards,
Max

[Nihil Roma Maius]

The VFA 90?

Maybe one of the best BFO was made by C-Scope. Read part of old post 01-18-2006. Diggerbarns wrote:

The best BFO I ever used was an Arado detector. The VFA 90. This had a search frequency of 9khz. This is very low for a BFO. This was mixed with a reference frequency of 9 mhz in some way. This was a very pleasant detectos to use. Great on a salt wet beach with very good discrimination against iron, and very stable. Wish I had kept it.

9 khz and 9 Mhz? Mix in the 1,000th armonics???

[Max]

Maybe one of the best BFO was made by C-Scope. Read part of old post 01-18-2006. Diggerbarns wrote:

The best BFO I ever used was an Arado detector. The VFA 90. This had a search frequency of 9khz. This is very low for a BFO. This was mixed with a reference frequency of 9 mhz in some way. This was a very pleasant detectos to use. Great on a salt wet beach with very good discrimination against iron, and very stable. Wish I had kept it.

9 khz and 9 Mhz? Mix in the 1,000th armonics???

Hi,
don't know if it's arado vfa-90... I know is probably a UK made product, think that would be something about 1978-1980... but I don't know more... and the person who own it can't remember which manifacture was ...now that stuff is in orrendous conditions due to the heavy use but still working as I know.

He said me that he requested the unit on suggestion of another person that used it before... and requested by a local dealer from manifacturer.

Could be an ARADO ?

"Mix in the 1,000th armonics???" uhm seems not easy task... cause you know that harmonics tend to drop amplitude with distance from foundamental. I don't know... but guess that beating freq. was obtained by mixers running at much higher frequencies...
I saw a BFO running around 700KHz! That's a crazy frequency for a metal detector... but it was an OFF-Resonance type. But performances were too bad... just 10-15 cm. And it becomed crazy with also a small piece of cigarette silver paper...

Best regards,
Max