Unbalanced coil...

[ivconic]

Hi, i would like to see if some other experiences with unbalanced coils..?
When making coil, everybody trying to gain as better balance as possible...which is quite normal.....
But experimenting with Classic 3 i made several different coils, few of them unbalanced and working very good.
Classic 3 by its conception is pretty simple device. Discrimination level is tuned with one pot. It is subjective, from case to case, at which level it will discriminate certain type of metal...I do not mind to know exactly what i detected with CL3...but to know accuratelly is it iron or "coloured" metal like bronze,brass,al,ag,au or cu....Since i already do know character and preferences of terrain, i only need that kind of simple discrimination....Therefore i noticed that slice unbalanced coil can go even deeper in some cases than balanced??? Stabillity can be gained through adjustments....
When i said "unbalanced", i ment one or less of windings of FB gives stronger TX field, but not so strong to "choke" RX...yet giving louder "echo" from detected object....
Am i right? Is it right way of thinking? This could not be taken generally....just in case when simple device is needed...
Any comments?
regards!

[Esteban]

Try tune in harmonic of transmitter frequency. In several cases, the detector works better in harmonics than central frequency. What happens if you try in the 5th harmonic, for example?

[Geo]

Hi Esteban and Ivconic.
One time i tuned a coil at 2th harmonic but on the air i had lower sensitivity. Maybe the only reason to tune at 3th harmonic is to transmit at 4.8...5 khz and receive at harmonic (14.4...15 khz) that is near the gold frequency.
Now about unbalanced coils !! VLF works with phase shift so no problem if the coil is not balanced but if the rx signal is very hight then the first ampl can't give gain because the output is saturationing. One time i made a detector from Elector with a DD coil and it says to balance the coil and after to unbalance it a little for better performance. I made it and yes it had right...with a little unbalance the coil was better but never tried it again.
So Ivconic maybe to have right
My Regards

[Max]

Hi, i would like to see if some other experiences with unbalanced coils..?
When making coil, everybody trying to gain as better balance as possible...which is quite normal.....
But experimenting with Classic 3 i made several different coils, few of them unbalanced and working very good.
Classic 3 by its conception is pretty simple device. Discrimination level is tuned with one pot. It is subjective, from case to case, at which level it will discriminate certain type of metal...I do not mind to know exactly what i detected with CL3...but to know accuratelly is it iron or "coloured" metal like bronze,brass,al,ag,au or cu....Since i already do know character and preferences of terrain, i only need that kind of simple discrimination....Therefore i noticed that slice unbalanced coil can go even deeper in some cases than balanced??? Stabillity can be gained through adjustments....
When i said "unbalanced", i ment one or less of windings of FB gives stronger TX field, but not so strong to "choke" RX...yet giving louder "echo" from detected object....
Am i right? Is it right way of thinking? This could not be taken generally....just in case when simple device is needed...
Any comments?
regards!

Hi ivconic,
I've the same behaviour with my last homemade coil for bandido. It's normal to have
sometimes better sensitivity with small unbalanced coil.

Can explain:
In TX-RX configuration you have to null RX signal to have stability and no saturation at
RX preamp but how you do it ???
Yes, counterwounding and bucking coils are solution. BUT when you NULL signal what you do
is reaching an equilibrium in opposite fields (well, in signals from e.g. tx transmitted fields
or rx received fields in rx-splitted-coils) and that equilibrium is NEVER perfect.
What I mean is that you reach some mV peak to peak of nulling at RX and then this voltage
is the "reference" point when no metal is near the coil.
OK. Have you never asked yourself what's better here ???
I mean that few mVpp can be obtained two ways (considering same side of the coil):
- over-balancing
- under-balancing
Because if you "ideally" balance...you have 0Vpp! But you have ever few mVpp not zero!

What I mean for under- and over- ? ok...
I refer to signal increase behaviour...the one you have when you slowly put object near
and near your coil watching at your scope...
Sometimes, what I call over-balancing, you have signal to null and pass through zero/gnd
potential before getting an increase of signal when nearing metal.
Sometimes, what I call under-balancing you haven't this behaviour and signal start to
increase when metal is near without need to pass through zero !
This depends also on shape, dimensions relatives and wounding schema.
In concentric-coplanar most of this behaviour is related to field lines patterns.

I notice that behaviours mostly with coin sized objects...other things greater show also the
same but very fast when you near them. So small object are to be used to identify behaviour.

The under-balancing gives you more sensitivity (often 5-10cm), because you don't lose some
small voltage by decrease-increase behaviour before getting signal increase detection, but
has big drawbacks... and this is most important:
-is more sensitive to gnd effects...
when you near coil to ground you get small signals
detected as targets. Yes, there is GND balance in good MDs but often you end-up with
lot of false signals even when you have done a right GND balance procedure first.

The reason is obvious: you can't sweep and held coil always at same height...and also if
you could (not human) terrain is never absolutely flat and with a perfect mixed matrix.
And if there are bricks/pottery things can go even worse, because they are anomaly in
the matrix, with mag moments very well aligned...you detect easy pieces of them at more
depth than with over-balancing.

I think so, that many manifactures chose the over-balancing because is "easy" and that
"initial inertia" in part cancels out many strange behaviours from their detectors.
I think that all original tesoro coils are this way and also many others commercials.
Reason is that they claim to have good GND balance and stable operations and also users
are often not skilled people but newbies.
In homemade coils we put our hands on...modifing things, but always you pay something for
sensisitivity increase--> stability, gnd-sensitiveness, pottery-detection etc

I prefer having stable operations and better gnd/pottery cancelling than having 5-10 cm
increase of depth (in theory) that then on the field make me crazy...with gnd, bricks etc
But I think other people may choose to have a bit more sens. tollerating some false signals.

What can I say ? Better is what you feel right for you (you know where you have to use your MD,
so terrain, contamination, external noise...).

Best regards,
Max

[Qiaozhi]

Hi, i would like to see if some other experiences with unbalanced coils..?
When making coil, everybody trying to gain as better balance as possible...which is quite normal.....
But experimenting with Classic 3 i made several different coils, few of them unbalanced and working very good.
Classic 3 by its conception is pretty simple device. Discrimination level is tuned with one pot. It is subjective, from case to case, at which level it will discriminate certain type of metal...I do not mind to know exactly what i detected with CL3...but to know accuratelly is it iron or "coloured" metal like bronze,brass,al,ag,au or cu....Since i already do know character and preferences of terrain, i only need that kind of simple discrimination....Therefore i noticed that slice unbalanced coil can go even deeper in some cases than balanced??? Stabillity can be gained through adjustments....
When i said "unbalanced", i ment one or less of windings of FB gives stronger TX field, but not so strong to "choke" RX...yet giving louder "echo" from detected object....
Am i right? Is it right way of thinking? This could not be taken generally....just in case when simple device is needed...
Any comments?
regards!

In theory there should be more sensitivity if you use a balanced coil. In practice (as Max stated earlier) it can depend on whether you under-balance or over-balance. It may also be necessary to tweak the circuit parameters to get any real benefit from a more carefully balanced coil. Unbalancing the coil too much can cause discrimination problems, particularly when the target is further away. In this case the RX signal may be weaker than the residual signal being generated in the RX coil by the TX circuit, and the phase shift introduced by the target is reduced. If you lower the residual TX signal by balancing more carefully, this may allow you to increase the gain of the RX preamp, but this in turn can cause instability, resulting in less sensitivity. At the end of day it all boils down to "compromise".

[ivconic]

Carl....

Carl is there any way to fix problems with this forum.....i have problems last few days....you already gave explanation but still problems!?


Now my post:

I ve been experimenting a lot with coils lately. Just few days before, decided to
make good concentric,coplanar coil for my White's Classic 3 copy. But i wanted to
keep it relative small (suitable for coinshooting), with diamm. not more than 20cm,
eventually 22-24cm...but not more.
So i made 5-6 different coils with different number of windings. I respected everything
i founded here on these pages and other more.
Finally i founded out how difficult...almost imposiblle is to make good concentric,coplanar
coil in amateur workshop. Also i learned much new things during those days. I realisied that
i didnt knew much about coils just few days before....and i still dont!!!?Sheesh!!!
It is not problem at all to make coil with fantastic depth (in air)! No, not at all!
When adjusting to gain more depth,usually man checking coil with one item - coin in most
of the cases. So i did that. I gained over 50cm detection on simple coin in the air!
But!.......That coil turns to be usellles on the ground, producing bedlam of false signals
all over arround!? I was desperate for some time. Later read G.Payne's hints and decided to
use piece of ferrite in conjuction with coin, when adjusting coils....So at one moment i got
no detection on ferrite at all, but still descent detection on coin.....BUT....i lost
discrimination!?!? Not able to discriminate iron at all???
So i spend more than few days "turning arround trying to catch my own tail" without any
succes!? Shhheeeesh!! I wasted tons of wires,coffe,nervs and.....nothing!?
Either i gain good detection with huge instabillity...either good stabillity and discrimination
with "puke" detection ....10-15cm on coin...Nothing!
So i keeep asking my self is it possible for me to make 20cm coil which is gonna be calm,stabile and
able to detetct a coin at ....let's say...25cm in the ground???
Best detector i used so far was Minelab Musketeer Colt with TS800 coil (18cm) and can detect
same coin at 22cm in the ground, very stabile - no false signals at all....But TS800 is also
double D coil......I want coplanar,concentric coil with that performances...
Is it possible?
About ferrite....what is the point? Should i adjust coil not to detect ferrite at all or oposite?
Can i use ferrite as reference in my lab when adjusting coil to be calm...as substitute for real
ground conditions....or my coil should make noise on ferrite?
I do respect G.Payne a lot, but i didnt understand him well....
Also i do respect Dave Emery a lot too.....but his theorems were unsuccsesfull in case of making
coil for Classic 3.....
It is very easy to balance coil and gain zero reading by adjusting nuber of turns on FB coil....
Few less or more, some measurements and you got it..coil is balanced! But that balanced coil
almost always turns to be not good, detect coin from 5-6cm to 10cm...nothing more...
Once i opened some original coil taken from White's Eagle II...i counted 396 windings in RX coil,
31 winding in TX coil and 11 windings in FB...???????????
Now, what kind of relation is that? That coil is beating all Daves claims about relations in
turns between TX and RX?????
Johnson patented very interesting coil under #4,293,816....I made that coil also....not good with
Classic 3 at all!!!
So....what to think? Anybody alive made good 20cm coil for Classic 3????
P.S.
Spare me of theory please....I do know all the theory so far...I am doctor of theory.....i just
need practice....

[Geo]

Hi Ivconic
I am doctor of practice. ....i just
need theory ....

The only way is to come here to Greece near me ... or the opposite
My regards

[Max]

Carl is there any way to fix problems with this forum.....i have problems last few days....you already gave explanation but still problems!?


Now my post:

I ve been experimenting a lot with coils lately. Just few days before, decided to
make good concentric,coplanar coil for my White's Classic 3 copy. But i wanted to
keep it relative small (suitable for coinshooting), with diamm. not more than 20cm,
eventually 22-24cm...but not more.
So i made 5-6 different coils with different number of windings. I respected everything
i founded here on these pages and other more.
Finally i founded out how difficult...almost imposiblle is to make good concentric,coplanar
coil in amateur workshop. Also i learned much new things during those days. I realisied that
i didnt knew much about coils just few days before....and i still dont!!!?Sheesh!!!
It is not problem at all to make coil with fantastic depth (in air)! No, not at all!
When adjusting to gain more depth,usually man checking coil with one item - coin in most
of the cases. So i did that. I gained over 50cm detection on simple coin in the air!
But!.......That coil turns to be usellles on the ground, producing bedlam of false signals
all over arround!? I was desperate for some time. Later read G.Payne's hints and decided to
use piece of ferrite in conjuction with coin, when adjusting coils....So at one moment i got
no detection on ferrite at all, but still descent detection on coin.....BUT....i lost
discrimination!?!? Not able to discriminate iron at all???
So i spend more than few days "turning arround trying to catch my own tail" without any
succes!? Shhheeeesh!! I wasted tons of wires,coffe,nervs and.....nothing!?
Either i gain good detection with huge instabillity...either good stabillity and discrimination
with "puke" detection ....10-15cm on coin...Nothing!
So i keeep asking my self is it possible for me to make 20cm coil which is gonna be calm,stabile and
able to detetct a coin at ....let's say...25cm in the ground???
Best detector i used so far was Minelab Musketeer Colt with TS800 coil (18cm) and can detect
same coin at 22cm in the ground, very stabile - no false signals at all....But TS800 is also
double D coil......I want coplanar,concentric coil with that performances...
Is it possible?
About ferrite....what is the point? Should i adjust coil not to detect ferrite at all or oposite?
Can i use ferrite as reference in my lab when adjusting coil to be calm...as substitute for real
ground conditions....or my coil should make noise on ferrite?
I do respect G.Payne a lot, but i didnt understand him well....
Also i do respect Dave Emery a lot too.....but his theorems were unsuccsesfull in case of making
coil for Classic 3.....
It is very easy to balance coil and gain zero reading by adjusting nuber of turns on FB coil....
Few less or more, some measurements and you got it..coil is balanced! But that balanced coil
almost always turns to be not good, detect coin from 5-6cm to 10cm...nothing more...
Once i opened some original coil taken from White's Eagle II...i counted 396 windings in RX coil,
31 winding in TX coil and 11 windings in FB...???????????
Now, what kind of relation is that? That coil is beating all Daves claims about relations in
turns between TX and RX?????
Johnson patented very interesting coil under #4,293,816....I made that coil also....not good with
Classic 3 at all!!!
So....what to think? Anybody alive made good 20cm coil for Classic 3????
P.S.
Spare me of theory please....I do know all the theory so far...I am doctor of theory.....i just
need practice....

Hi ivconic,
don't know for sure 20cm coplanar-concentric for classic 3...but think not so different e.g. from bandido I maked ...following mike's instructions.
Concepts are always the same...just "tuning" is a bit different one to another...I mean expecially for phase shift.
I've used classic 3 only with original coils...can't say about homemade.
But think they can be close to other coils described in the forum. There is somewhere a KT315 post with details for white's too.
I think that, once the coils are ok on workbench, what's very important is shielding. If shielding modify phase shift something is wrong (too thikness etc).

I found my coil for bandido is working very well mantaining phase shift.

I've used AWG30 for both tx and rx. Worked ok.
Think that with proper inductances 20cm and 12cm tx-rx configuration could be ok also for classic 3.

Best regards,
Max

[Qiaozhi]

It is not problem at all to make coil with fantastic depth (in air)! No, not at all!
When adjusting to gain more depth,usually man checking coil with one item - coin in most of the cases. So i did that. I gained over 50cm detection on simple coin in the air!
But!.......That coil turns to be usellles on the ground, producing bedlam of false signals all over arround!?

It sounds to me like your homemade coil is out of the tuning range of the CL3's GEB circuit.

You should be able to test this with a dual-beam scope. Connect channel 1 to the input of the analog switch associated with the GEB channel, and channel 2 to the gate input of the same switch. Then try adjusting the GEB control and check that the gating pulse is sampling at the zero-crossing point of the input signal. Alternatively (for a single channel scope) you can monitor the output of the analog gate for a null, while adjusting the GEB control.

A similar problem may be happening with the DISC channel. In this case the gating pulse should be sampling near the peak of the input waveform.

[ivconic]

Friends!


First to Carl; now all is working fine! Last few days it was almost imposiblle to open forum....but it seems that problem is solved....it works even faster! Bravo!

To Geo; yes Geo, i would like to meet you one day. We can go on the field and search for coins etc...I ve been visiting Greece some 50 times so far....I even lived on Creta island for 2 years...I like Greece so much..and i miss Greece a lot.But there is constant problem with visas so i cant come there....
This summer i would like to spend 15 days in Greece enywhere on the coast...but i have to figure way how to get visas for me and my familly....Greek consulate ask to many papers, i can provide all...problem, huge problem! So it seems that only way we meet is you to come and be my guest here in Serbia. Anyway, here is nice too.I live in very famous spa, popular touristic destination here...Few terrains also here, roman and byzantine....We can talk about that until summer!

Quiaozhi, Max,Geo...friends, thanks you a lot! It is not problem to me to make anu double D coil....but problem is to make small c.c. coil....Huh!
Yes, you might be right....i have to find some good osci. and try all over again.... I think Bandido look like coils not suitable for Classic at all. It seems that Classic is transmiting at one freq. but receiving some harmonic or simillar...cose ratio between Tx and Rx number of windings is more than 5:1...more like 12:1 pr even more???
When aplying some ordinary coil to CL3 it is working, but weak....i tried many times to adjust some oder coil....at the end it works pretty average...
Except spider coil for Fisher CZ series...?? Why? I dont know. Even that coil is working a bit better than average...
I'll see....
thanks and best regards!

[Max]

First to Carl; now all is working fine! Last few days it was almost imposiblle to open forum....but it seems that problem is solved....it works even faster! Bravo!

To Geo; yes Geo, i would like to meet you one day. We can go on the field and search for coins etc...I ve been visiting Greece some 50 times so far....I even lived on Creta island for 2 years...I like Greece so much..and i miss Greece a lot.But there is constant problem with visas so i cant come there....
This summer i would like to spend 15 days in Greece enywhere on the coast...but i have to figure way how to get visas for me and my familly....Greek consulate ask to many papers, i can provide all...problem, huge problem! So it seems that only way we meet is you to come and be my guest here in Serbia. Anyway, here is nice too.I live in very famous spa, popular touristic destination here...Few terrains also here, roman and byzantine....We can talk about that until summer!

Quiaozhi, Max,Geo...friends, thanks you a lot! It is not problem to me to make anu double D coil....but problem is to make small c.c. coil....Huh!
Yes, you might be right....i have to find some good osci. and try all over again.... I think Bandido look like coils not suitable for Classic at all. It seems that Classic is transmiting at one freq. but receiving some harmonic or simillar...cose ratio between Tx and Rx number of windings is more than 5:1...more like 12:1 pr even more???
When aplying some ordinary coil to CL3 it is working, but weak....i tried many times to adjust some oder coil....at the end it works pretty average...
Except spider coil for Fisher CZ series...?? Why? I dont know. Even that coil is working a bit better than average...
I'll see....
thanks and best regards!

Hi ivconic,
yes white's seems to be different from tesoro coils.
E.g. dfx concentric has something:
rx 13.8 mH 36ohm
tx 540uH 2.7ohm

So it's true they are different where tesoro's have similar inductances.
Tesoro seems working on fundamental frequency also on rx stage, where white's not. I agree.
I think it's because using harmonics it's easy to avoid too coupling between tx-rx due to imperfect balace in the air-core-transformer and also to gnd mineralization.

Seems that white's homemade requires much more care to keep them working. They require much experimentation than tesoro.

But I think that previous post by Quiaozhi is very useful with any geb/vlf machine to figure out if there is something wrong in gnd cancel section.

I think that shielding could be made with graphite without having much problems, where e.g. foil could be too critical here.

Best regards,
Max

[Qiaozhi]

First to Carl; now all is working fine! Last few days it was almost imposiblle to open forum....but it seems that problem is solved....it works even faster! Bravo!

To Geo; yes Geo, i would like to meet you one day. We can go on the field and search for coins etc...I ve been visiting Greece some 50 times so far....I even lived on Creta island for 2 years...I like Greece so much..and i miss Greece a lot.But there is constant problem with visas so i cant come there....
This summer i would like to spend 15 days in Greece enywhere on the coast...but i have to figure way how to get visas for me and my familly....Greek consulate ask to many papers, i can provide all...problem, huge problem! So it seems that only way we meet is you to come and be my guest here in Serbia. Anyway, here is nice too.I live in very famous spa, popular touristic destination here...Few terrains also here, roman and byzantine....We can talk about that until summer!

Quiaozhi, Max,Geo...friends, thanks you a lot! It is not problem to me to make anu double D coil....but problem is to make small c.c. coil....Huh!
Yes, you might be right....i have to find some good osci. and try all over again.... I think Bandido look like coils not suitable for Classic at all. It seems that Classic is transmiting at one freq. but receiving some harmonic or simillar...cose ratio between Tx and Rx number of windings is more than 5:1...more like 12:1 pr even more???
When aplying some ordinary coil to CL3 it is working, but weak....i tried many times to adjust some oder coil....at the end it works pretty average...
Except spider coil for Fisher CZ series...?? Why? I dont know. Even that coil is working a bit better than average...
I'll see....
thanks and best regards!

Can you post the correct schematic for the transmitter and receiver circuits?
I seem to have three different versions, and two of these have the tuning caps missing on the RX.
Can you also provide the TX and RX coil inductances.

[ivconic]

...


Well...i am respecting original Classic I schematic mostly...i already posted pcb of CL3 which is almost the same with CL I except extended voltage comparator+led diode+few minor changes, those not concern anyhow RX and TX parts...so; there is a 1nf cap parallel to RX, but there is not any cap on pcb for TX...rest of caps are in search head...arround 1uF for TX and maybe some for tuning RX-depends of coil.
With Fisher Spider coil i am using 330nF for TX and 32nF for RX.....
Frequency is adjustable from 6.35kHz to 6.9kHz...
I do not have any original White's coil right now to measure inductance...so..
I also have several schematics of CL3 already posted here..I think those all are correct and usable. Diferences are only at caps due various coils used with those...Maybe KT315 or Geo can say something about right values?
I was thinking to calculate number of RX windings using 3rd or 5th harmonic and than check...but i am not sure?
Mostly White's coils are versatile, ,may be used on different machines...I do know for sure that 6000DI/Pro and Classic 3 can share same coils....for example very good....excellent Blue Max coil etc...
Well.....neeed more datas....yet
regards!

[Qiaozhi]

Well...i am respecting original Classic I schematic mostly...i already posted pcb of CL3 which is almost the same with CL I except extended voltage comparator+led diode+few minor changes, those not concern anyhow RX and TX parts...so; there is a 1nf cap parallel to RX, but there is not any cap on pcb for TX...rest of caps are in search head...arround 1uF for TX and maybe some for tuning RX-depends of coil.
With Fisher Spider coil i am using 330nF for TX and 32nF for RX.....
Frequency is adjustable from 6.35kHz to 6.9kHz...
I do not have any original White's coil right now to measure inductance...so..
I also have several schematics of CL3 already posted here..I think those all are correct and usable. Diferences are only at caps due various coils used with those...Maybe KT315 or Geo can say something about right values?
I was thinking to calculate number of RX windings using 3rd or 5th harmonic and than check...but i am not sure?
Mostly White's coils are versatile, ,may be used on different machines...I do know for sure that 6000DI/Pro and Classic 3 can share same coils....for example very good....excellent Blue Max coil etc...
Well.....neeed more datas....yet
regards!

Using the Fisher coil as an example, I've done some quick calculations:

Let's say the TX frequency is set to 6.5kHz. In that case (with Crx=32nF and Ctx=330nF) the TX coil inductance calculates as 18.74mH, and the RX coil inductance as 1.82mH.

Now - to make a smaller coil (Tx inner diameter of 200mm, and RX inner diameter of 100mm) with the same inductance values would require 61 turns for the TX and 336 turns for the RX, using 0.56mm wire.

As you can see there is a large ratio between the number of turns on the TX and RX coils, just as you have found. From these calculations and studying the schematic I do not believe that this design is making use of harmonics. The use of harmonics is a technique that has been employed in the past in some BFO designs in order to increase sensitivity, but I cannot see that there would be any advantage here for an IB detector. It appears to be tuned to the fundamental.

[ivconic]

....


I think you are pretty close! (or maybe i am pretty close...?)
My "best" coil so far has 43 turns in TX and 310 in RX....but not same wire...I used 0.2mm for Rx and 0.4 for TX....
You mentioned 0.56mm wire...? Huh, i cant imagine those 330 windings with 0.56mm wire on such small diamm. of 10cm....pretty "bulky" isnt it?
Can you recalculate RX with thinner wire, lets say 0.2 or o.25mm ?
By the way,thank you very much for helping here!
Regards!