One coil induction metal detector

[neazoi]

Hello I have found this circuit

http://www.aha.ru/~aish/book2/final.htm

It is the most complex metal detector I have seen, more complex than the magnum one, yet it uses just one coil.
I am a bit confused, what type of metal detector is? PI or IB ?
The magnum is the most advanced DIY metal detector I have seen, what about this one? is it better or not? Please make a review.

[Qiaozhi]

Hello I have found this circuit
http://www.aha.ru/~aish/book2/final.htm
It is the most complex metal detector I have seen, more complex than the magnum one, yet it uses just one coil.
I am a bit confused, what type of metal detector is? PI or IB ?
The magnum is the most advanced DIY metal detector I have seen, what about this one? is it better or not? Please make a review.

The text is very difficult to read and understand due to the peculiar "English" that's been used. However, it is clearly not a PI or an IB. From what I can determine, it appears to be a relatively complex off-resonance detector. This is one-step up from a BFO. Some rudimentary discrimination is achieved, as non-ferrous targets will cause the amplitude to change in the opposite direction to ferrous targets.

It does not appear to be a very powerful detector, with a detection depth for a 25mm coin of 150mm (~6").

[neazoi]

Thank you for the information.
Could you suggest me a good IB detector from this page http://www.geotech1.com/cgi-bin/page...e=projects.dat
I think the magnum is a good one and there are instructions of how to build the coils.
Or maybe another dual mode (PI IB) detector?

Any better suggestions from this or other pages?

[Davor]

The way I see it - it is an IB kind of thing. It works exactly as the GB/Disc in common IBs work, by Tx signal deduction and multiplying a remaining signal with ~90 degree carrier etc. There is nothing wrong with this approach, except that off-phase Tx noise passes through undiluted, hence low sensitivity.

Using dual coil IB geometry suppresses both Tx and its noise, so it works better.

[neazoi]

The way I see it - it is an IB kind of thing. It works exactly as the GB/Disc in common IBs work, by Tx signal deduction and multiplying a remaining signal with ~90 degree carrier etc. There is nothing wrong with this approach, except that off-phase Tx noise passes through undiluted, hence low sensitivity.

Using dual coil IB geometry suppresses both Tx and its noise, so it works better.

Thanks, I got an idea now of how this works using a single coil.
What do you think about the magnum?

http://www.geotech1.com/cgi-bin/pages/common/index.pl?page=metdet&file=/projects/magnum/index.dat

In article reading it seems quite powerful.
Have you got a design better than this?

[Davor]

It works exactly as every other IB around, except the way GB/Disc controls are done in one single channel. The only big difference with nowadays MDs is that there is a 2 quadrant phase detector in every one.

The only difference that I think is done better in Magnum than in nowadays detectors is a low impedance preamp. Those were the times when you couldn't buy a half way decent opamp regarding noise, so BJT preamps were a commonplace. What is not so obvious when using a low impedance input is the way Rx and Tx coils interact. Nowadays IBs use low noise opams in their frontend, and instead of low impedance a coil is configured in a semi-tuned LC tank configuration. In effect a Rx coil sees a low but frequency dependent impedance, while opamp sees a high impedance, so everyone is happy. However, being near resonance, phase conditions change due to changing ground proximity - an effect not present with real low impedance input.

I am starting my IGSL build in a day or two (family maneuvers at hand) and I am considering trying a low impedance input

[neazoi]

Do you have any better metal detector to propose, for the home builder, than the magnum? I like the magnum because it has many modes and it gives exact instructions of how to build and align the coils. I have not found a more detailed article, have you?

[Qiaozhi]

Do you have any better metal detector to propose, for the home builder, than the magnum? I like the magnum because it has many modes and it gives exact instructions of how to build and align the coils. I have not found a more detailed article, have you?

Try this ->

http://www.geotech1.com/forums/showthread.php?t=15710

[neazoi]

Try this ->
http://www.geotech1.com/forums/showthread.php?t=15710

I agree this is very detailed as far as concern the coil winding! Excellent.
It has a dual channel as well to help discrimination.

What other characteristics make is better than the magnum one?
I mean what are it's features, apart from the ones I mention above, it is not very clear from the article and I cannot see any meters. The potentiometers are just 3 as well...?

[Davor]

It should work as good as magnum, but with much more straightforward discrimination. Plus there are many people who built it recently and you'll have their support all the way.

[neazoi]

It should work as good as magnum, but with much more straightforward discrimination. Plus there are many people who built it recently and you'll have their support all the way.

All right thank you!
They also have different types of coils. The magnum uses a pin-point coil which could be better for finding other sizes (and depths) of targets, whereas the tgsl uses a wide scan coil (which is easier to build indeed).

Also (correct me if I am wrong) the magnum may be more helpful in finding non precious metals (why one should want this?), since the TGSL is pre-set for non ferrous metals?

[ace4188]

Hi, is any one here frm south africa,i want to knw where in s.a i can buy a pi pcb with components,tried silverdog in the uk but no joy

[Carl-NC]

The GoldPic project is from Trevor Hill in SA, go here:

http://home.global.co.za/~trh