Dear Max tgsl

[metaldetector107]

thanks alot Max
but i am abit confused what u mean by tank?
capacitor u mean
and also free oscillator? should i make another oscillator
or u mean external probe of scope?....
As you said
my tgsl TX is exactly 14.7 and RX 14.5
is there an easy way to get RX frequency for example what should i change to get required frequncy for RX..
i am measuring RX freq via TX pole..
Max i am using a very good digitial meter called JT-168
very acurate now pin12 abit less than half of pin1
last question does the inductance increase or decrease when caging coil?
best regards

[Max]

thanks alot Max
but i am abit confused what u mean by tank?
capacitor u mean
and also free oscillator? should i make another oscillator
or u mean external probe of scope?....
As you said
my tgsl TX is exactly 14.7 and RX 14.5
is there an easy way to get RX frequency for example what should i change to get required frequncy for RX..
i am measuring RX freq via TX pole..
Max i am using a very good digitial meter called JT-168
very acurate now pin12 abit less than half of pin1
last question does the inductance increase or decrease when caging coil?
best regards

Hi,
don't need a new thread each time, use this to make other questions if needed please... otherwise big confusion here.
Ok, the tank is the "resonant tank" , in other words it's in our case the L and C circuit that determines which frequency of resonance you'll see. In rx section you have exactly that, a coil and a capacitor connected in parallel way that's our resonant tank.
The free oscillator is a circuit you can make to put in an arbitrary resonant tank (again a coil and cap in parallel as example) and get oscillation from that: the frequency of oscillations generated is by (ideally) only the values of inductance and capacitance at tank, so the free oscillator is anything (e.g. a transistor circuit) that when you put there a resonant tank will mantain oscillations and give you possibility to take e.g. measures. If you search old threads you could find a circuit I posted many months ago... of a free oscillator that could be used from low freq. (some khz) to some hundreds Mhz (actually used also for vhf stuff and other things by me in past).
The stimulus coil, instead is a coil that you'll use to inject a signal (by magnetic couplig with rx coil) : the signal you could get from e.g. a function generator, so you can choose e.g. frequency , change it... or amplitude also... that way you could see measuring at rx tank the received signal and so find the resonant frequency (frequency at which you get maximum amplitude reading at rx tank); but you need scope for that kind of measures.
The frequency at rx tank you'll adjust (if required) by little modifications at capacitor there: like add or sub 100pf at a time to/from it. But stability you must check then on soil.... cause sometimes it's easy getting good results about increase of performances on the bench, then big false signals on real soil... cause changing cap at rx tank means also changing residual voltage , so alter nulling of coil.

ps: depends on cage material, with thin aluminium cage you'll get usually few hundreds hz less when cage is applied (means more inductance than when no cage, same apply if you tight bound wires more using e.g. tape... more inductance if wires are closer than before...), that's depends much on thickness of foil etc and distance from copper wires, if e.g. there's tape between etc.

Kind regards,
Max

[metaldetector107]

TGSL

Dear Max
i am realy confused i dont understand is it possible to explain it agin but easly please?
how about maching TX with RX frequency
cuz i dont understad resonance why seprate coil?
please i know i am troubling you but i have no choise

thank alot
best regards

[Max]

try to make it easier....

Dear Max
i am realy confused i dont understand is it possible to explain it agin but easly please?
how about maching TX with RX frequency
cuz i dont understad resonance why seprate coil?
please i know i am troubling you but i have no choise

thank alot
best regards

Hi,
it's simple, you need to match tx inductance and rx inductance to make a good coil, then null it.
Now the inductance is due to many factors not only number of turns. You right pointed to effects of shielding and that's an issue, there are others like taping the wire tight, the more the more inductance you get at same number of turns etc

The free-oscillator strategy is only if you are perfectionist and wanna hi precision on resonant frequency, don't need really in most of the cases.

You need to match inductance, so at tx you'll do so when will find the tx frequency stay in the expected range : that you need when coil already shielded etc so at the end the frequency must stay in the limits described.

For rx the stuff is similar, but remember that in e.g. Tesoro's coils the rx coil has a bit more inductance, usually 6.2mH there like described in the table I wrote about... the link I posted.

Now if for tx coil you just need to match frequency (say 14.7Khz as example) and that with expeceted values of capacitor at tx oscillator, of course, for rx coil you need a step further ahead, some turns more there.

In tgs coil by Ivconic you'll see some numbers like 100 turns for tx coil... and 105 for rx coil: fine you have 5% more turns at rx, and something more inductance.... so if tx will be for example 5.8mH you'll get about 6.2 mH at rx coil that way.

As example make 6.2/5.8 = 1.068 (about) that means you'll get about 6.8% more inductance there... with 5% more turns.

That's cause inductance increase NOT linearly with turns number... but that's unimportant here... what you need is a bit more inductance at rx coil: that's cause this will give you the right phase shift at coil when on nulling phase, that's all we need to know, and tesoro made that way for this purpose.

So, leave all considerations about exact resonance at coils, and try to focus only on inductances and required phase shift/nulling of coil.

Much of what I wrote before is advanced stuff... needed just when try to put things on the extreme of performances.... but often boring and unuseful if you just need a working md.

Kind regards,
Max

[metaldetector107]

tgsl coil

Dear Max
i have made your coil from p105
new (gigantic ?) 12'' coil for TGS
Hi all,
I've made a new one...for teh collection... this is a 12''DD for TGS, as well as other uMax models, can use too.

Here's actual recipe:

wire 0.25mm bare (30AWG)
TX turns = 88
RX turns = 92

TX resistance is about 24ohm
RX resistance is around 25ohm

TX L = (about) 5.7mH
RX L = (about) 6.15mH

For those who need MUCH depth... [IMG]file:///G:/new/m/forum/TESORO%20GOLDEN%20SABRE%20-%20Page%20105%20-%20Geotech%20Forums_files/lol.gif[/IMG]

Can get a coin at 50cm (half-crown)! [IMG]file:///G:/new/m/forum/TESORO%20GOLDEN%20SABRE%20-%20Page%20105%20-%20Geotech%20Forums_files/biggrin.gif[/IMG]

1eur at 42-43cm , in disc mode......

So max i got same value
how many milihenry should by difference between TX ands RX coil
to get best depth?

[simonbaker]

1eur at 42-43cm , in disc mode......

That's the best depth I've heard of... I'd like to see more specifics on your design.

-SB

[Max]

That's the best depth I've heard of... I'd like to see more specifics on your design.

-SB

Hi,
yes I know... but also Ivconic made similar claims on smaller coil (the usual DD for tgs tuned Ivconic's way,do you remember the video on youtube ?) consider mine it's a big diameter coil anyway, so the improvement on depth is direct consequence of increased diameter not that the coil is anything different from others.

Sure a goo nulling (and phasing) is essential in that coil.... but same for all others... otherwise false signals and bad disc will be sure fact.

Now... I would add details but I can't , my home lab was "packed" (dismantled and stuff packed in a safe place) cause I need extra room for other stuff so I simply can't find at now anything included the coil and documents about... so you guys must stay with informations posted before on the TGS'thread. Are about accurate an you can replicate the coil.

But, consider also that these readings and performances were on very good pcb thing already tested ok with other coils. Noise is the big issue, if circuit is too noisy you won't get that range whatever you do. So use best parts and cut as much noise as possible from pcb.

Kind regards,
Max