Not wrong!

[Anonymous]

First , I enjoyed yours reactions, this prouved I am not wrong...
Second, i read every day the Forum ( Mr.Bill) and I participate sometimes, SINCE the beginning , years ago...
Third, SINCERELY everybody, if you check the technical knowledge last years or before (remenber when Eric speak about to write a PI book), IT WAS GOOD, very good level in PI tecnical research , it was a PI CLASSROOM !!!! for many of us.
Finaly, I Know IT IS NOT ERIC'S FAULT but OURS because we do not participate enough to bring new technical papers on the table...
And finally , I do not feel it is a stupid comment!!! - human being has the right to express himself freely and it is thanks to the marvelous way of Internet WWW and it genious creators.....
Alex.

 

[Anonymous]

Alex... You expressed yourself better this time. I now see what you meant to say, and my "stupid" remark does not apply. You're right, there's not as much technical talk as there use to be, maybe because there's nothing new to say. Don't forget, this forum is for both the tech guys and the non-tech guys. If people ask questions about certain brands, there's nothing wrong with that. Everything works in cycles, so sooner or later you'll see more technical info. <IMG SRC="/forums/images/smile.gif" BORDER=0 ALT="">

 

[Anonymous]

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[Anonymous]

This forum was not started just for the technology minded people only. The purpose of the forum was to inform All who were interested in PI design, and operation, correct information. There was, and still is a lot of mis-information out there about the PI detector, and how it works.
This forum works because it is geared toward all users of the PI detector, not just those that desire technologic information. The end user is the big reason we are all here. With out them, where would the designers be ? We need input from the end user so those that are designers, and engineers can learn if there moving in the proper direction.
This is a commercial site. Meaning that someone has to pay to maintain this page. With me it

 

[Anonymous]

Hi Alex
Yes, there is a bit advertising of course. But if you don't like it than don't read it.
My mailbox at home receive every day many ads. as well. I just ignore them and read the interesting one only.
Don't be angry with my comment on this..... I just want to let you know that there is another PI FORUM without ads. in the net. Check it out www.pulsdetekor.de
It's a German speaking forum & with good PI projects. Some of the conversation is in English. If there is a post written in German and you don't understand German than you can use a web translator and reply in English.
For your info. Most of the Germans can speak English.... Maybe not perfect. But I notice that many Americans have problems with there own language too (if you read there comments...in forums, on ebay, chat rooms...etc).
Or swap to the geotech forum at
http://www.thunting.com/cgi-bin/geotech/pages/forums/index.pl
This forum is quite good.
Chris

 

[Anonymous]

Well said Mr Bill, loved the saying "one hand washs the other", great sense of humor ,but also reality.
JMhammered

 

[Anonymous]

[No message]

 

[Anonymous]

Eric is one of a very few commercial detector designers (three, total, that I'm aware of) who will even discuss detector design. You won't get this from Garrett, White, Gifford, Candy, or any of the engineers working for their companies. But, as an illustration, if Jack Gifford were to start a VLF tech forum, it would probably center around Tesoro detectors. I would expect that, and be damned thrilled that he was willing to share any tech info at all.
I think a whole lot of people have benefitted from Eric's forum (I know I have), and those who own one of his PI detectors probably have one of the best made.
- Carl

 

[Anonymous]

Alex,
How about sharing with us details of the tests that you did with mono versus DD coils, and explain why you say that DD is a waste of time. That would be a good technical contribution to the forum and no doubt start a thread of discussion that would be independant of any specific detector?
Eric.

 

[Anonymous]

Hi Alex,
I like Eric's idea about a discussion comparing DD coils to mono coils on a PI, and I also hope you will share your viewpoints in greater detail on this subject.
I am curious just what size coils you have built and how they compare depth wise to a similar sized mono coil.
I am also curious as to why you feel that a DD coil has little advantage in reducing ground signal. I suspect the reason is because of the type of ground where the experimenting was done.
So far, I have built 4 different sized DD coils, a 11" round, a 8 1/2" by 11", a 10" by 14", and a 11" by 16". I have also used the same forms to build mono coils and even have experimented with figure 8 coils in the same forms.
By the way, for people interested in trying to build their own coils, all of the above size coils were made using pre-formed ABS plastic housings made either by Rick Schroeder or Bill Hays (Hays Electronics). The forms make building the coils much easier, at least assembly wise.
At the present time, the 11" round housing has to be modified to get the proper width of overlap. However, Bill Hays informed me he will be working on another form that should work properly. Also, Rick Schroeder is also working on a form that will be about 9 1/2" by 14 1/2".
Reg

 

[Anonymous]

Hello forum,Like I say i did some test using two coils .one to transmit and the another to receive Eric give the name of CONCENTRIC coil.
The big one is 11" for transmit ,inductance is 330 uH (the same for the mono coil) and the smaller one is 8 inch inductance is 1000 uH o 1 mH.
First I adjust for both coil the R damping for no ringding it give me 380 R for the trans. and 1 K 1 for the receive,then i installe and balance physically the two coil one in the center (R) of the another (T) with the best geometric i can,for that i use now a nice test coil it is a form board for designer , you can make your circle o D ,cut with Xknife and with a solder pen you burn a little to make a small channel where yours coil wires goes,with this technique you have a exact coil diameter with it center.
For my test in the workbench i simulate a hot mineralised ground with a red brique ( like you use in construction house) and I have also a collection of hot rock .....
With the detector and a 11" mono coil i have a treshold sound for a nickel at 30 -32 centimeter and a repeatable good signal at 27cm with indication in the signal meter...AIR TEST !!!
with the concentric coil (T/R) ...25 cm ...air test .
and for detecting the red clay the concentric give me 3 cm down in comparaison with mono.Not great for me , but to give me a better result i make the concentric coil (with my PVC techniK) and go to check in the field because you can see the real thing far from the electricals interferences....It was the same result , in a hightly mineralised ground ( i live in a silver mineralised mining zone) the CC give me a LITTLE more signal just perceptible in the Smeter, but NOT the claiming of many publicity coils advertiser....just a little better two ; three cm for a nickel and if you see the weight and the two embarassing cables ,two connectors coil and the switch in the box i prefer the mono coil, and also years ago i make the 8 configuration and many forms with T center etc... for the same not many improvment ....
In the hightly mineralised ground your signal for a nickel shut DOWN to 15 ,18 cm for a nickel ,yes at 250 mA of power transmit coil.......
I live also in the pacific coast ,here it is different some sand beach are complete neutral , your AIR test is the SAME as the GROUND test, but also you have mineralysed black copper sand with mica , and adios your search you shut down to 10 cm for the nickel.........and IT IS the TRUE reality , i check with more and more power to go to 500Ma transmit coil and nothing because in this time you receive also the same magnetised ground ............
For my detector i worked with the Basic Foster design front end (709 or 5534) with 2K2 input R -TX width 100uS,pulse delay variable from 10uS to 80uS Fcy is 660 and 1200PPs ,Sample is 20uS -MosF 740-two channels with two samples like the Goldscan design with manual pot for gnd cancel (it is the only effective design for working in a hightly mineralised ground like here in Mexico) treshold audio stage and Smeter signal energetised power with the very effective and old design of the pump charge 555 two transistors boost of the GS ( +6V - 6V , -12V, ground is the positive path) or direct for 740 coil ) and for close this door ; a pack of Nimh of 14V4 ( 12 of AA ,1600 Ma ) .Alex
Ps: when you adjust the coil receive in the coil transmit you must see with oscillo the signal , if it is inverted you must invert the receive coil turning in the other side and the signal reappears inverted allright...

 

[Anonymous]

Alex
The concentric coil design you describe should reduce the ground signal, but it will not reduce it as much as a DD design.
The signal you get back from a small piece of ground depends on the distance from the transmit coil to that piece of ground and the distance from that piece of ground to the receive coil. In a mono coil the transmit and receive are the same coil and the distance from the piece of ground to the coil can be very small when the coil is close to the ground. This can give a very strong ground signal.
In the concentric design a small piece of ground can be close to the transmit coil or it can be close to the receive coil, but it cannot be close to both of them at the same time. So the concentric design does not give as strong a ground signal as the mono.
In the DD design the transmit and receive coils are overlapped in a way that cancels out the ground signal. If the ground is uniform then for every small piece of ground that gives a signal there is another small piece of ground that gives exactly the opposite signal and the two cancel out. Of course real ground is not uniform so the canceling is not perfect, but the ground signal will be less than in the concentric design.
In both the concentric and DD designs the target signal will fall off faster with distance than the mono design does. So you should get less range in an air test than you do with a mono coil. But in very bad ground the DD may reduce the ground signal enough that you can detect targets deeper than you can with a mono coil.
In weak ground the mono coil should be able to detect deeper, and the 2 coil designs will be heavier and more complex than the mono. So for someone who detects in weak ground most of the time the 2 coil designs are probably a waste of time. But in bad ground there should be some times when a DD would pay off.
Robert

 

[Anonymous]

Hi Alex,
Thanks for the information. I am not sure why your are experiencing the distinct difference in depth capabilities between the concentric and the mono coil.
I only tried a concentric coil briefly and wasn't pleased with the results. However, at the time, I was concentrating on ground signal reduction and not on depth, so I do not remember just how my concentric coil compared depth wise.
Now, all of my DD coils I make, are made with two identical coils, both in size and inductance. One is the receive and the other is the xmit. Both are about 430 uh each. One side of each coil overlaps the other in the center. The overlap is approximately 2" wide, but does vary from end to end.
Even with my smaller elliptical coil, the 8 1/2" by 11" coil I can get an air test of about 13" to 14" on a nickel. I have also used this coil to try a buried nickel test. I buried a nickel about a foot deep in a drywash having a heavy concentration of black sand and was able to detect it with a very decent signal. Actually, I tried this about 3 times in different locations to verify the depth capabilities.
I have also built a somewhat strange round 11" DD coil with about the same inductance as the smaller one and, was able to obtain about 16" to 17" with a very weak signal from a nickel. Again, this was under ideal conditons where there was almost no noise. However, on regular days with noise present, 15" air test depth capability is more common.
I am operating my detector with a 10 usec delay when making these tests.
In a nutshell, I have not seen any real depth loss between the DD and the mono coil. I suspect that if I were testing using much bigger targets then I would see a greater difference.
I do see a significant ground signal reduction on the DD coil, and also experience a softer signal from really small gold (less than 7 or 8 grains in size). The noise levels are down on the DD coil also. The DD coils are extremely quiet.
In the case of the small gold nuggets even down to the 3 grain size, I seem to get very close to the same depth, air test wise as I do with a mono coil, but the signal intensities are different. Buried nugget tests approach the air test capabilities depth wise also. Right now, I attribute the similar depth capabilites to the fact that the DD coil is so much quieter.
Reg

 

[Anonymous]

Hi Alex,
Many thanks Alex, for posting more information. I tried a concentric coil on a PI some time ago, but the main reason was to be able to do some discrimination. Certainly, I would have expected the range to be less, as it is equivalent to a single coil somewhere between the two diameters, shifted a little bit one way or the other, depending on the ratio of the inductances.
I have not yet had time to look at a DD coil in much detail, but Reg has come up with some interesting results. Also, many reports from Australia, in areas of high iron mineralisation, indicate that a DD coil performs better in that situation.
One thing that I find intriguing, is that DD coils appear to be electrically quieter, enabling greater ranges than a mono to be achieved in some conditions. Certainly the RX coil in an 11in DD is considerably smaller than an 11in mono TX/RX coil, and this will help. However, the benefit appears to go a bit beyond that.
I once did some tests that indicated that the transmitter introduced noise into the RX circuit, even when it was switched off between pulses. I remember on one occasion, having to select the TX mosfets for low noise in the off state. If it really was the case that the TX introduced noise, then a balanced DD coil would remove this. It may of course be noise from other sources that is being passed via the capacitances of the mosfet, rather than being generated in the mosfet itself. Maybe better filtering in the TX supply rail would help.
Along with low noise amplifiers, this is an area that would benefit from more investigation.
Eric

 

[Anonymous]

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