Unbalanced coil...

[Qiaozhi]

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!

With 0.2mm wire the RX coil needs 309 turns.
With 0.25mm wire the RX coil needs 313 turns.

If I use 43 turns for the TX coil with 0.4mm wire, the inductance is 0.97mH, which seems too low. The resultant TX frequency would be 8.9kHz.

It's a little tricky to calculate easily because of the feedback winding. I presume you are building a concentric coil, or is it a double-D or double-O?

[ivconic]

C.C.Coil...


Concentric Coplanar Coil - c.c. coil....I do not have problems with DD or OO coil...

I repsected your latest calculation and made that coil....Bust! Detect coin on 5-6cm....Later i balanced it better....26 turns on FB...so i gained zero volts on RX coil, with or without parallel cap. on TX....Than i put 100 nf parallel to TX and gained detection on coin at 15cm distance....much better but i lost discrimination!? So i spend 2-3 hours trying to solve problem but without succes....

I suppose your calculatons are not proper....sorry...Best result so far was with 310 turns on RX and 43 turns on TX with mentioned caps...with full discrimination...
I think 60 turns for TX is way to much....I ll try tomorow with turns between 38 to 45 on TX....
There must be some small thing i dont know yet about this CL3...?
I never had simillar problems with other detectors!? I dont have doubts in this specific unit cose i do have 4-5 already made CL 3's and i can switch them in cirlce while testing and adjusting....all behave same?

So.....?
regards!

[Max]

Concentric Coplanar Coil - c.c. coil....I do not have problems with DD or OO coil...

I repsected your latest calculation and made that coil....Bust! Detect coin on 5-6cm....Later i balanced it better....26 turns on FB...so i gained zero volts on RX coil, with or without parallel cap. on TX....Than i put 100 nf parallel to TX and gained detection on coin at 15cm distance....much better but i lost discrimination!? So i spend 2-3 hours trying to solve problem but without succes....

I suppose your calculatons are not proper....sorry...Best result so far was with 310 turns on RX and 43 turns on TX with mentioned caps...with full discrimination...
I think 60 turns for TX is way to much....I ll try tomorow with turns between 38 to 45 on TX....
There must be some small thing i dont know yet about this CL3...?
I never had simillar problems with other detectors!? I dont have doubts in this specific unit cose i do have 4-5 already made CL 3's and i can switch them in cirlce while testing and adjusting....all behave same?

So.....?
regards!

Hi ivconic,
do you use an oscilloscope or a meter to do the nulling ?
I ask you because when I nulled my last coil I get it nulled under 1mV peak to peak with the scope then measured also voltage with a digital meter (Metex M-3650) and have about 25mV measured in ac !
Then I've used a workbench type of multimeter getting 2mV (hung chang).
Then a lafayette meter that reads 4-5mV.
Another unknow brand "battle meter" signs 43-45mV !
So I concluded that the first meter was inaccurate at low ac voltages (10KHz range). The others are better but not as I want.
If you use digital meter you need a very good one with a large bandwidth say at least 30KHz in AC or you need to build a preamplifier like in old analog BF voltmeters (just one op. amp needed) to having hi sensitivity at ac in the 10KHz range of frequency.

I guess that your disc doesn't work because of too much signal feeded in when you tune for max sensitivity.

Best regards,
Max

[Qiaozhi]

Concentric Coplanar Coil - c.c. coil....I do not have problems with DD or OO coil...

I repsected your latest calculation and made that coil....Bust! Detect coin on 5-6cm....Later i balanced it better....26 turns on FB...so i gained zero volts on RX coil, with or without parallel cap. on TX....Than i put 100 nf parallel to TX and gained detection on coin at 15cm distance....much better but i lost discrimination!? So i spend 2-3 hours trying to solve problem but without succes....

I suppose your calculatons are not proper....sorry...Best result so far was with 310 turns on RX and 43 turns on TX with mentioned caps...with full discrimination...
I think 60 turns for TX is way to much....I ll try tomorow with turns between 38 to 45 on TX....
There must be some small thing i dont know yet about this CL3...?
I never had simillar problems with other detectors!? I dont have doubts in this specific unit cose i do have 4-5 already made CL 3's and i can switch them in cirlce while testing and adjusting....all behave same?

So.....?
regards!

Can you tell me the exact dimensions (inner diameter) you have used for the coil that works? Also, can you measure the inductance values for the TX, RX and FB coils, and let me know the capacitor values used in both cases.
I will then do a more serious investigation.
And one last thing - I need to know the TX oscillator frequency.

[ivconic]

Whaaatttt????


I just answered a long answer and try to post and got message that i am "timed out" !!!!!??????? **** this nonsence forum!

[Geo]

I just answered a long answer and try to post and got message that i am "timed out" !!!!!??????? **** this nonsence forum!

Relax my friend
We find itself in the dangerous age
Please send your email at [email protected].
Maybe to stop here
My regards

[Unregistered]

40 turns TX , 300 turns Rx.......2cm coin at 24cm distance.....calm no false signals, very stabile....

[chemelec]

I just answered a long answer and try to post and got message that i am "timed out" !!!!!??????? **** this nonsence forum!

Probably your Server did that, not this site.

[ivconic]

......


Not my server but this forum !
Puke!
I am angry....i do not want to talk!
Heh,heh,heh...!
Best regards Gary,Quiaozhi,Geo....others!

[Carl-NC]

Sorry... for what it's worth, it's happened to me... ALWAYS TYPE UP LONG RESPONSES IN A TEXT EDITOR... do the ol' copy-paste... this is true FOR ANY FORUM. I'm hoping vBulleting will add a "Save-as-Draft" option on the next major rev.

[ivconic]

...


I usually do. Using notepad, prepare post, than copy&paste here....
But the other night i wanted to answer "on the fly" to Quiaozhi, so i write....and write...and write....Sheeesh! It was novel! And the "thing" happenned....
Problem is that i forgot what i wanted to say than, so right now i cant write it again....
Point is that (to Quiaozhi) i didnt moved any further with c.c.coil....same results!? Best (if i may say so) is 43Tx 310RX...as i mentioned early....
No progress?
Regards!

[ivconic]

Question !


Question for all interested here!

I usually put both coils in Faraday cage-Al foil. I am asking if any differences in cases when only one coil is in F.cage ?

What is the point? When to put RX, when TX, when both? In what cases?
Differences?
Best regards!

[Max]

Question for all interested here!

I usually put both coils in Faraday cage-Al foil. I am asking if any differences in cases when only one coil is in F.cage ?

What is the point? When to put RX, when TX, when both? In what cases?
Differences?
Best regards!

Hi ivconic,
difference is higher on rx coil...if you unshield it...but also tx frequency/amplitude vary without the faraday shield when nearing to ground.
I think that on good VLF coils both need shielding at least with graphite if not with aluminium or other metals (nickel).
When rx is unshielded you get false signals every time you near it to the ground cause static charges gives transients on movements thus revealed as target...no way.
On tx unshielding gives similar behaviour but with less falsing cause you have weak coupling between tx and rx coil (air core).

You can test on existing coils e.g. DD simply disconnecting shield cable to gnd. The presence of e.g. foil doesn't mask statics this way...and you get false signals.

Too capacitive effects there and you have big problems try to find some useful signal...

Best regards,
Max

[Geo]

Hi Ivconic . The best shielding is the shield of both windings. Once i made a shielding with semiconductive tape. The tape length was not so big, so i shielded the tx winding and the half Rx. Results..... detector was unstable . When i shielded all the rx winding the detector came stable
Regards

[Max]

Hi guys,
I've tested my DD 22cm coil on my (little) test garden...
Got 22cm depth for 20 eur-cent and 30cm (weaker sound) for 1 eur coin !

Seems good...but I've noticed that on deeper target, 1 eur coin, I get less sound...but there is a small halo too.

I buried the coin about 1 year ago...don't understand why I get with lower sound. Ground contains some bricks and pottery fragments I've inserted to give indications of false signals generation in detectors.

With good geb setting I can cancel out many smaller fragments signals...but then continuing detecting well non-iron metals in disc mode.

Anyway I think that bandido works good with DD 22 cause I've tested too with smaller coins and got about 20cm depth (for 1 eur-cent).

Coil is balanced (nulled) at 1mV pk-pk and tx-rx are both 120 turns 0.3mm.

When 9x8 arrives I'll make a comparision between 22DD and it to figure out major differences.

Best regards,
Max