Multi-Frequency

[Davor]

It will help. I'm not saying you'll get more depth, because whenever you apply some sort of GB you lose some sensitivity. In that sense a pure all metal 2boxx is optimal for depth. However, multifrequency shall remove any mixture of ground and air, so I expect to have some edge with multifrequency over a difficult ground.

[Skippy]

I have done some investigation, and with the aid of "Google Translate", I have found this thread on md4u, where the Sovereign is discussed. I think there may be some useful info there, I have not looked hard.
https://translate.google.co.uk/trans...D77%26t%3D2227
Original page:
http://md4u.ru/viewtopic.php%3Ff%3D77%26t%3D2227

[Davor]

Unfortunately not. Timings and schematics are slightly wrong.
You might feel the whiff of simplicity there. The silliest thing is that you may produce a housewife-proof device that way and mass produce it for peanuts. The only reason major companies don't do it already is perhaps a fear of cannibalisation of the existing markets. You really can have a proper rig that is literally turn-on-and-go.
IMHO it is the principle worth following. Copying an existing device is not my thing. I don't think people at md4u grasp the working principle at hand.

[Skippy]

I suppose the Russians main interest in reverse-engineering is to help repair broken machines. Then academic interest will perhaps encourage further study. But few people would actually want to 'make their own', when the ML machines perform such a competent job as standard.
As I can't read a word of Russian, and the translation is patchy, I didn't give the thread more than a quick look.

[rickb]

Clarification needed

I would like some clarification of the voltage/current waveforms of the fbs/bbs detectors. Carl posted this http://www.geotech1.com/forums/attac...2&d=1426351535

This from the Minelab document.
http://p.briggs.home.comcast.net/~p....VED_SIGNAL.JPG

There is a big difference in the coil t/c or pulse width between the 2 current waveforms. Carl shows the higher freg pulsetrain integrated almost out of existance whereas the Minelab drawing is not. Is the difference meaningful or not relevant in terms of discrimination? Do the waveforms represent no target or ground influence?

Rick

[Carl-NC]

My waveforms are of the transmit voltage and current. Minelab shows the transmit voltage (blue) and a receive voltage (red) for a ferrous target. They don't show a current waveform.

[Larry WA]

Hello, new here.
Very interested in multifrequency VLF machine for mineralized areas, salt beach and other here in the Pacific Northwest (Washington State).
Just missed out on getting a Whites V3i for an excellent price.
Interested in a diy model. Have reviewed the multifrequency threads here, but have not seen any schematic or kit.
Is this a realistic diy goal?
Thanks.

[Davor]

Not yet.
Key Minelab patents that enable serious simplifications expired, but there are no amateur builds available.
You may find a Fisher schematic, but it is waaaay too complicated.

[Skippy]

"Is this a realistic diy goal?"
Sadly, it seems too great a step to make. It sounds like what you are wanting is what the commercial machines do well, so you should simply buy one of them, and get digging.
My main interest in dual/multifreq is related to making a machine that isn't like the commercially available ones, and that just adds a load more complexity.

[Larry WA]

I know almost zilch about electronics so please forgive my ignorance. I know there are several pulse induction machine designs out there-- Gary's at Chemelec, the Surf PI and others, and that PI machines work differently from very low frequency machines. I've been told a VLF machine is more complicated than a PI machine, but I don't understand why-- VLF machines have been around for a long time. I'm also wondering if it makes a significant difference whether one approaches this from an analog or digital perspective.
Two questions for now:
Why is it more difficult to build a VLF machine?
If there is someone who has built a VLF, how complicated would it be to add a (digital) function to broadcast and receive a set of frequencies? Could that be done with a pitch or sweep generator?
Thank you.

[rickb]

"I know almost zilch about electronics"


Time to start learning. Step 1, buy this book.

http://www.amazon.com/Inside-Metal-D...Metal+Detector (Written by the moderators of this forum and required reading if you are really serious about this.)

If, after reading it several times, you don't have a fair understanding of what's involved in building an I/B or PI detector and the theory behind their operation, then buy a commercial detector. You need the parts, test equipment, and experience to be successful even with a relatively simple detector. Spend a few weeks reading threads about others attempts, some successful, some not. It's not as easy as you seem to imply in your last paragraph. I could say a lot more, but more reading on your part will provide a better understanding.

[Larry WA]

Hi, Rick-- just found out about the book day before yesterday, and it's on my list to buy-- I'm sure you're right, it's not as easy as one might think.
Thanks.

[rickb]

Read the forum for this book.

http://www.geotech1.com/forums/forum...Metal-Detector

Don't buy it from the idiot on amazon trying to sell it for $49. It's only $29. And worth every penny.

[Davor]

Bottom line of various nowadays technologies:
- VLF has solid discrimination, sucks at salty beaches and heavily mineralised soil, has at least two channels in Rx, and therefore a bit more complicated.
- PI has flimsy discrimination - if any - but excels at beaches, seriously expensive machines work well on highly mineralised soil, easy build if you go for a beach detector.
- multi-frequency technology comes at various degrees of complexity, and discrimination, works for housewives and professionals alike, sadly, no amateur builds.

[Math]

post #43 ..id like to take up this challenge

ive been here around 10 years now and electronics was a mystery to me before i found this forum
thanks to everyone involved here who contribute in a positive way and keep this running ..ive learnt so much
time for me to give something back.. im still far from expert at electronics and will need putting right on much of the analog side of things but i will begin a design based on the new pic16f18426..
it has some excellent digital and analog peripherals, i believe 14 pins is all we need
for anyone whos not used a pic microchip before.. all you need is to download mplab software (free) and buy a pickit3 programmer (~£10) once you get started its easy to learn from the chip datasheets and mplab help.. i just use the basic assembler code around 50 instructions no need to learn C programming for this design.. i will post code up along the way

TX waveform we can generate from the DSM data signal modulator peripheral
It will be a multi frequency detector that is in harmony with the energies of our planet rather than working against them
Beginning at the Schumann resonance.. we have the fifth partial around 34hz.. the fifth of this brings us to 171hz
In music this is the note F3 at the 432hz (original) tuning.. from re-examining the work of Alexander Thom we find this is the tuning ancient sites around the globe were built to, energies here are both on and off planet and everything is electromagnetic energy. Taking the note F up in octaves to the light spectrum we find its the only note that lies outside of the visible. Its the link to the moon that Thom strove for.. being in harmony with the moon diametric.
Enough mumbo jumbo..

Pic clocked at 8Mhz we will use the PWM peripheral TX frequencies... 856hz for the DSM carrier signal.. x2 = 1.712khz for our low frequency on the first half wave of our carrier.. we will be using this for our iron discrimination and x8 = 13.7khz for our high frequency on the second half wave of the 856hz carrier.. this is our primary non ferrous detection frequency

Using a tuned coil resonant frequency to match our high frequency rather than the low one.. designed for 4x 13.7khz = 55khz resonant coil frequency we’re aiming for.. using this formula to design our coil TX and RX inductances and resistances (wire gauges)...

55khz coil factor = 55x55(squared) x 0.018 = 55(coincidence) and coil factor = Rsum divided by Lsum = Rtx x Rrx divided by Ltx x Lrx

Lets go for a 1mH TX with a 4x RX @ 4mH... then Rsum = coil factor x Lsum = 55x4 = 220R..

designing 8” coil turns and gauges.. back later