Originally posted by ivconic
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FINALLY !!! (capitals...ts,ts,ts...must be a crackpot?)
Finally i made coil,i always wanted to make!
But first i'll name conditions for "dream coil";
- It has to be small, smallest as could be!
- It has to be round, due comfort in movements,
- It has to be very sensitive on small (very small) items,
- It has to be deep....and I MEAN DEEP !
Only one coil i met so far fullfilling those requirements;
it was Minelab TS 800 coil (18cm)
1cm coin (i usually use for testing coils) it can detect at 22cm
in the air and 18cm in the ground!
So......
I made Golden Sabre and it showed pretty good performances with
two "casual" coils i made fast - "on the fly", last few days...
Yesterday i took TS 800 coil and redraw its shapes on plain paper...
And i done some calculations and made BEST coil so far...!!!
It is double D coil.....here is datas so you can make, test and
check my claims:
RX = 178 turns, 0.25mm wire (0.28mm with varnish), 23,6 ohms
TX = 165 turns, 0.25mm wire (0.28mm with varnish), 21,4 ohms
How can i explain former...? Huh? Here is photo of it. Diammeter of
whole coil (both DD shapes put togather,tuned and nulled) is 18.5cm...
so try to imagine how to make former...
I used Al foil for both coils as Faraday cage. Over foil i wounded
few windings with plain, naked (without varnish) wire to make good
conntact with foil. Over all i wraped simple adhesive tape to
consolidate, brace all...and that is all!
The rest, about nulling....you already know, i do not need to repeat here.
Coil performances are ....WOW !
Same coin it detecting over 30cm in the air!!!!! Much better than TS 800!!!
Cigarretes package at 45cm, cola can over 52cm.....
For coin:
Up to 25cm audio tone is loud,sharp and stiff!!! Over 25cm audio tone is
decaying step by step and a bit over 30cm it ends....WOW !!!
(up to 25cm constant flux, over 25cm it decreases....read bellow)
Promising....promising!
I'll have to wait until tomorow to test it on the ground. Few more steps left
to finish it; put in some suitable case,glue it...wait until drain...get dry...
I think i discovered "big secret" about coils...somehow...!?
Problem about depth is not closely related only to size of a coil. Much more
important thing is flux, magnetic flux! Density of magnetic field that TX
part producing...
It is not immaterial relation between size of a coil and wire gauge used in it!
How can i explain?
The higher density of magnetic field coil is producing - the better!
If choosing proper wire gauge than no need for much power on TX. Simple 2N2907
can do the job just fine. BC557 also.
Unlike in Anker detector and simillars, you dont need extra powerfull TX to gain
some depth! No not at all! Even oposite, powerfull TX is more like to "choke"
RX input and than another problem occurs - hums,false signals,interferences....
Totally unusable on the ground, especially on highly mineralized ones!
At the end, frequency is playing huge role when deciding about coil size and wire
gauge....I had luck (must admit) with this Golden Sabre, due its 14kHz frequency!
In the past i had a lot of "pains" and troubles trying to make Classic 3 go deeper
with small coils....no wonder!
So at the end conclusion;
"Larger" flux could be gained if preciselly chosen wire gauge and coil diammeter.
How to do that?
I dont know!
I dont have a clue!
I just had luck, this time!
Heh,heh,heh...!
Best regards!
your DD seems is like my homemade...but I've used mylar/al on shielding instead of foil. The other parts are similar...but I've used 120 turns for both tx and rx cause I need 10KHz on bandido. Used rx flat then tx bounced over.
Get very good results in air.
Yes, I think that tx flux is an essential part of success here, but you need to consider than what's truly important is signal-to-noise ratio in this kind of detectors cause power is always limited respect to e.g. pulse induction type.
And the guys at tesoro knows what they do...I mean they used good schematic strategies to improve S/N and also (like in e.g. bandido) "special" components to physically reduce noise at operating frequency. This way they get outstanding performances that mainly depends on coil parameters cause S/N in the circuit is always controlled and stable. So if you use e.g. a DD coil you could get much less problems e.g. from mineralization where using concentric you could get better pinpointing. Also wire gauge is important cause oscillator is small power colpitts and current depends mainly on coil too.
What to say...with proper coils I think that many of these detectors are still actual cause have good performaces in ground and only lacks are in display/mcu that are absent and present e.g. in Cortes or other newer. But they are good...general purpose VLF. So far, bandido is the best VLF I've mounted myself ! I had problems with components at first and with concentric...but it's clear that is a powerful design , really stable with right things in the circuit. And GoldenSabre is much like it - if not better !
I told you that DD works great on bandido...then your GS will appreciate DD too also on the ground I think.
Best regards,
Max
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