VLF/PI Hybrid.

[Crumble]

Hi all, new to the forum. I was thinking about detector design, and am contemplating a hybrid vlf/PI machine... 2 seperate circuits, 1 multifrequency vlf, and 1 PI, in the same box, with a knob to switch between the 2. To me it seems like an obvious solution to the PI vs multifrequency vlf machines debate. Hunt in PI mode, and switch to vlf mode for the disc. On the deep targets dig out a few inches of dirt/sand to get in range of the vlf mode for disc. Pretty much how a lot of Excal users already hunt, but with a 4 inch or so depth advantage with a dedicated PI circuit in all metal mode. If you used a coil similar to the dual field coil, in vlf mode it works like a concentric, outer transmits, inner receives, in PI mode both coils transmit, then both receive.

I primarily beach hunt, using an Infinium LS, and soon will be buying an Excal/CZ for the trashy beaches. A hybrid vlf/PI would be revolutionary IMO, is there any reason why it can't be done? May be an interesting project to work on. So many guys trying to come up with a way to discriminate on a PI machine, this seems like a much easier solution...

Any thoughts on this?

[Qiaozhi]

Hi all, new to the forum. I was thinking about detector design, and am contemplating a hybrid vlf/PI machine... 2 seperate circuits, 1 multifrequency vlf, and 1 PI, in the same box, with a knob to switch between the 2. To me it seems like an obvious solution to the PI vs multifrequency vlf machines debate. Hunt in PI mode, and switch to vlf mode for the disc. On the deep targets dig out a few inches of dirt/sand to get in range of the vlf mode for disc. Pretty much how a lot of Excal users already hunt, but with a 4 inch or so depth advantage with a dedicated PI circuit in all metal mode. If you used a coil similar to the dual field coil, in vlf mode it works like a concentric, outer transmits, inner receives, in PI mode both coils transmit, then both receive.

I primarily beach hunt, using an Infinium LS, and soon will be buying an Excal/CZ for the trashy beaches. A hybrid vlf/PI would be revolutionary IMO, is there any reason why it can't be done? May be an interesting project to work on. So many guys trying to come up with a way to discriminate on a PI machine, this seems like a much easier solution...

Any thoughts on this?

As often happens, someone already thought of this [obvious] idea.
http://www.google.co.uk/url?sa=t&rct...Pex22Q&cad=rja

[Carl-NC]

As often happens, someone already thought of this [obvious] idea.

Looks like you have to switch coils to switch modes. A while back I designed a TX circuit that would drive an IB coil either as VLF or PI, with the goal of combining an MXT with a TDI, and the ability to switch back & forth on the fly. Never built it, tho.

[Crumble]

Looks like you have to switch coils to switch modes. A while back I designed a TX circuit that would drive an IB coil either as VLF or PI, with the goal of combining an MXT with a TDI, and the ability to switch back & forth on the fly. Never built it, tho.

After searching around, multifreq vlfs seem to be shrouded in secrecy... The PI circuit is no problem, information everywhere on designing/building them, but seems I would have to design the multifrequency vlf circuit from scratch... Is there no info anywhere on multifrequency vlf machines? Schematics? Seems that multifrequency technology is defended fiercely... Technology moves forward much faster when the technology is shared between groups...

[Carl-NC]

At least on these forums, there is not much MF info because there has been little interest in MF. It's really not all that difficult, perhaps someone would like to introduce a project?

Also, there are a few patents out there which do a credible job of describing MF techniques, but patents are typically hard to wade through.

[Crumble]

At least on these forums, there is not much MF info because there has been little interest in MF. It's really not all that difficult, perhaps someone would like to introduce a project?

Also, there are a few patents out there which do a credible job of describing MF techniques, but patents are typically hard to wade through.

Yeah, I was just looking at minelab's multifrequency patent. How were they even allowed to patent multiple frequencies?! Aren't you not allowed to patent the obvious...

[Mrand]

The hybrid detector exists already for a long time. Systems PI and VLFwork simultaneously and are complementary to one another. At present I can't write more because the patent application progresses.
Mrand

[Crumble]

Nice looking machine you got there!

Happen to be multifrequency vlf?

I need to buy/make myself one of these machines for beach hunting...

[golfnut]

The other option is a decriminating PI - there are a few around.

There is a guy on here eho had a patent for one, also candy had one recently with drwgs that looked the same.

[Taktyk]

Hi,

The combination of fields is not so easy - must provide tangible benefits. Two detectors in one box is not a method .. I do not even know if it is worth. They benefit from the study of signals, different in the time domain and in the time frequency. You have to really desire and experience to combine these two different poles.

Regards
Taktyk

[Rumcajs]

Hi all, new to the forum. I was thinking about detector design, and am contemplating a hybrid vlf/PI machine... 2 seperate circuits, 1 multifrequency vlf, and 1 PI, in the same box, with a knob to switch between the 2. To me it seems like an obvious solution to the PI vs multifrequency vlf machines debate. Hunt in PI mode, and switch to vlf mode for the disc. On the deep targets dig out a few inches of dirt/sand to get in range of the vlf mode for disc. Pretty much how a lot of Excal users already hunt, but with a 4 inch or so depth advantage with a dedicated PI circuit in all metal mode. If you used a coil similar to the dual field coil, in vlf mode it works like a concentric, outer transmits, inner receives, in PI mode both coils transmit, then both receive.

I primarily beach hunt, using an Infinium LS, and soon will be buying an Excal/CZ for the trashy beaches. A hybrid vlf/PI would be revolutionary IMO, is there any reason why it can't be done? May be an interesting project to work on. So many guys trying to come up with a way to discriminate on a PI machine, this seems like a much easier solution...

Any thoughts on this?

Hi all,

it is similar to my think... yes, in this case must be switching between circuits. But what is about VLF-coils?
For example if PI-coil is 22 turn, and VLF DD-coil is 100 turn, the VLF circuit is receive cca. 5-times higher voltage input, than voltages induced in the PI coil (air core transformator). It is only one.

If VLF-coil is disconnected, maybe higher voltages... if disconnected and shorted VLF-coil while PI working (short circuit): it is no good way;
1) lost power heating it -- battery life time is shorter;
2) dramatically decreasing the primer impedance (PI coil properties), when secunder circuit is shorted (transformator).
3) What is ground balancing a mainly (re)tuning(!) VLF with disconnected coil (thermal stability, ect.)?

Therefore i m thinking an ,,VLF-modulated'' PI circuit is better way: for example the PI circuit sending the approx 150-200Hz pulse to coil, while the pulse is modified with 5-10kHz VLF-signal and both detector receive our own signals. The (audio) output maybe mixed or periodically switched with an 20kHz(?) multivibrator. It is my idea (theory) only, producing numerous owful paper sketch, but currently no complete circuit dwg or PCB. Technically are very problematic the number of turns in the VLF receiver coil (with paralel supressor diode), and the VLF coil thermal stability (tourist frequency ) while PI-coil is heating it.

Good hunting!

Rumcajs

[Rumcajs]

Or another way:

http://www.freepatentsonline.com/7701337.html

Hybrid-technology metal detector
United States Patent 7701337

http://www.freepatentsonline.com/7701337.pdf



Brg

Rumcajs

[Sean_Goddard]

patents are typically hard to wade through.

Especially if they are padded out with made up stuff, plain BS, or copies of other peoples (when you don't understand the initial concept) Like Br**e C***y's ones!!

[Davor]

Sure, but this one has some interesting features. It applies weighting function (sine) which is much easier to amplify than the raw PI Rx. Using a chopper instead would work fine too, but this one is nice.

[mickeu]

Is good idea, i know this MD but UOD workers in company "SPEC-MAJ" who ordered this MD for battle mine clerance was'nt happy with this project. Sensitivity arround 20 cm for frag. grenade is not hihg standart for now. With the price os Garret AC PRO it will be nothing interesting.