Max IVconic TGSL help

[metaldetector107]

Hi max ivconi and all
please help
due to too many different ideas in this forum could you please tell me
1- best TX freq
2-best RX freq
3-tx inductans
4- rx inductance
5- how to measure RX freq

many many thanks

[Max]

Hi max ivconi and all
please help
due to too many different ideas in this forum could you please tell me
1- best TX freq
2-best RX freq
3-tx inductans
4- rx inductance
5- how to measure RX freq

many many thanks

Hi,
1. for tgs/tgsl ? anything from 14.00Khz to 14.75Khz is fine; can use higher also, but you must change timings to keep stuff aligned.... so stay within that range if you don't know how to adj other stuff. From my experience higher part of that range is more interesting (at least for me) ...usually I haven't there anything lower than 14.60Khz that using all my "real" coils
2. rx-freq is due to resonance at rx tank , so depends on capacitor and inductance there.... you need to stay with reported values there, and just try add or sub some capacitance (say 100pF at a time) to match best performance, but keep in mind you'll alter also nulling doing so, so this is a test you'll made when have something already tested on soil and working... then change capacity, test on bench and the on soil again, if increased performances BUT same stability on soil or still acceptable you'll stay with that new value for cap.
3. 4. look at here: http://www.geotech1.com/cgi-bin/page...oils/index.dat
the values are about 5.7mH for tx coil and 6.2mH for rx coil for tesoro's standard umax coils in the 8'' range, same apply to other size of coils... look at table for further reference
5. can you put in resonance rx tank ? (yes you can) Use a free oscillator or give and external stimulus (like a sinus wave signal or other kind by external coil) to rx tank (coil+cap) and read (with a scope) the peak of amplitude : at maximum peak you have resonance so, measuring frequency on scope you'll get the right frequency of your rx tank when use stimulus coil , change the frequency of stimulus signal till get the maximum amplitude; the free-osc instead give you already what you need, the resonant frequency of the tank.
You can do by math also, but need very accurate measures of cap and inductance there.... though not accurate as the "direct" way you'll approximate much the real value using the resonance formula f= 1/(2*pi*sqrt(L*C)).

Kind regards,
Max

[simonbaker]

resonance

Interesting about resonance, I happened to be checking my RX resonance the other day.

My RX coil is 6.47 mH. You would think its resonance would be too low, turned out too high!

I checked resonance using signal generator and oscilloscope and frequency counter. I put a 1K resistor in series with coil and checked for max voltage across coil. Of course this requires signal generator with very constant voltage.

I was surprised resonance was at 17.5 kHz. My capacitor was a little low, about .0135.

I was losing about 14% of peak value (my TX freq is 14.2 kHz).

So I think it is worth checking RX resonance and adjusting capacitor to get the most out of your RX coil.

Regards,

-SB

[Esteban]

My method
First, the turns of the coils must be well fixed with barnish or similar product. There are very rapid dry barnish. But better is to wait 24 hours.

Many hobbyist or constructors calculate the resonance cap (s) without the shielded cable. This is an error. You must found the best resonance point with the final cable of your coils. Cables add many pF.

When you are near the resonance point adding capacitance as Max refers, connect in paralell a small plastic AM tandem 365 pF and found the best. Don't touch this. Disconnect the capacitors system (this include the variable 365 pF) of the coil and read the total capacitance added in parallell. For example, you read 12.456 nF. Select of all 12 nF you have in stock the approximative to this, but a little less to this value.

Connect only this and added final few necessary pF. No ceramic low quality, yes mica or styroflex. Use ever good quality capacitors, of this deppend in great manner the stability. Better if capacitors are for 150 to 200 V.

With this method, maybe you need 2 caps in paralell. Now you're in terrain of full resonance. Always use the same capacitance meter for all measurements.

Is like a radio. If your radio is bad tunning, how is the quality of you're listening?

[simonbaker]

Max:

2. rx-freq is due to resonance at rx tank , so depends on capacitor and inductance there.... you need to stay with reported values there, and just try add or sub some capacitance (say 100pF at a time) to match best performance, but keep in mind you'll alter also nulling doing so, so this is a test you'll made when have something already tested on soil and working... then change capacity, test on bench and the on soil again, if increased performances BUT same stability on soil or still acceptable you'll stay with that new value for cap.

Why would changing resonant freq by capacitor change nulling? Should be just physical placement of coils, shouldn't it?

Regards,

-SB

[metaldetector107]

TGSL coil

Dear Max and other
1-i need the the exact frequency value for TX and RX
2- the best inductance value for TX and RX

and no more

best regards

[simonbaker]

Hi,
1. for tgs/tgsl ? anything from 14.00Khz to 14.75Khz is fine; can use higher also, but you must change timings to keep stuff aligned.... so stay within that range if you don't know how to adj other stuff. From my experience higher part of that range is more interesting (at least for me) ...usually I haven't there anything lower than 14.60Khz that using all my "real" coils
2. rx-freq is due to resonance at rx tank , so depends on capacitor and inductance there.... you need to stay with reported values there, and just try add or sub some capacitance (say 100pF at a time) to match best performance, but keep in mind you'll alter also nulling doing so, so this is a test you'll made when have something already tested on soil and working... then change capacity, test on bench and the on soil again, if increased performances BUT same stability on soil or still acceptable you'll stay with that new value for cap.
3. 4. look at here: http://www.geotech1.com/cgi-bin/page...oils/index.dat
the values are about 5.7mH for tx coil and 6.2mH for rx coil for tesoro's standard umax coils in the 8'' range, same apply to other size of coils... look at table for further reference
5. can you put in resonance rx tank ? (yes you can) Use a free oscillator or give and external stimulus (like a sinus wave signal or other kind by external coil) to rx tank (coil+cap) and read (with a scope) the peak of amplitude : at maximum peak you have resonance so, measuring frequency on scope you'll get the right frequency of your rx tank when use stimulus coil , change the frequency of stimulus signal till get the maximum amplitude; the free-osc instead give you already what you need, the resonant frequency of the tank.
You can do by math also, but need very accurate measures of cap and inductance there.... though not accurate as the "direct" way you'll approximate much the real value using the resonance formula f= 1/(2*pi*sqrt(L*C)).

Kind regards,
Max

Max: to answer his question, first can you tell us why choose Rx coil inductance at 6.2 mH, since with .015u capacitor gives resonance at 16.5 kHz while oscillator is around 14.5 kHz?

I never understand why not choose resonance at oscillator freq.

Regards,

-SB

[Qiaozhi]

Max: to answer his question, first can you tell us why choose Rx coil inductance at 6.2 mH, since with .015u capacitor gives resonance at 16.5 kHz while oscillator is around 14.5 kHz?

I never understand why not choose resonance at oscillator freq.

Regards,

-SB

The answer has to do with keeping the design stable and making the design easier to manufacture.

There are two parameters that affect the initial phase shift between the TX and RX coils. The first is the physical coil arrangement. (i.e. the overlap between the two coils) and the second is the tuning of each coil. You can easily see this by comparing the TX and RX waveforms on an oscilloscope, while triggering from the TX signal. The coil setup is a compromise. Of course, you can try to tune both the RX and TX circuits to the same frequency, but then you will need to adjust the coil overlap to get the correct initial phase shift for the GEB and DISC circuits, but then the preamp will be overloaded by the increased residual voltage from the RX coil.

For the Tesoro designs it is more important to have the correct residual voltage and initial phase shift, than to tune the coils to resonance. To use resonant coils, you need to use a different design.

[simonbaker]

The answer has to do with keeping the design stable and making the design easier to manufacture.

There are two parameters that affect the initial phase shift between the TX and RX coils. The first is the physical coil arrangement. (i.e. the overlap between the two coils) and the second is the tuning of each coil. You can easily see this by comparing the TX and RX waveforms on an oscilloscope, while triggering from the TX signal. The coil setup is a compromise. Of course, you can try to tune both the RX and TX circuits to the same frequency, but then you will need to adjust the coil overlap to get the correct initial phase shift for the GEB and DISC circuits, but then the preamp will be overloaded by the increased residual voltage from the RX coil.

For the Tesoro designs it is more important to have the correct residual voltage and initial phase shift, than to tune the coils to resonance. To use resonant coils, you need to use a different design.

Referring to TGS design, I don't see how RX tank (RX coil and .015u cap) resonant frequency affects phase of RX signal -- it is always in phase with dphi/dt of TX, isn't it? Just amplitude should change. Because tank circuit is not phase-shifting element where it is located I think. But not sure.

Maybe most important for pinpoint mode (non-motion), I'm not too familiar with that mode.

Regards,

-SB

[Qiaozhi]

Referring to TGS design, I don't see how RX tank (RX coil and .015u cap) resonant frequency affects phase of RX signal -- it is always in phase with dphi/dt of TX, isn't it? Just amplitude should change. Because tank circuit is not phase-shifting element where it is located I think. But not sure.

Maybe most important for pinpoint mode (non-motion), I'm not too familiar with that mode.

Regards,

-SB

Try the experiment with the oscilloscope and you see that I am correct. You can also see this in a SPICE simulation (if you wish) by plotting the amplitude and phase versus frequency.

[simonbaker]

Try the experiment with the oscilloscope and you see that I am correct. You can also see this in a SPICE simulation (if you wish) by plotting the amplitude and phase versus frequency.

Yes you are right. I need to study this more.

So maybe RX tank resonant freq is a critical factor we should pay more attention to and do fine adjustments with capacitor, not just rely on coil inductances.

Question is: what is best RX tank resonant freq and why?

Regards,

-SB

[Max]

Max:



Why would changing resonant freq by capacitor change nulling? Should be just physical placement of coils, shouldn't it?

Regards,

-SB

Hi,
depends of what you mean for nulling. If you mean minimal voltage you're right cause depend on magnetic coupling between tx and rx coil.

But if for nulling you mean the absolute value of residual voltage, well, if you change resonant freq. of rx tank you'll get more of less depending of displacement from tx frequency if geometry is unchanged.

Do you understand what I mean ?

So, as example, if you find a good "nulling" meaning a value at wich device works nice on bench and on soil without saturation of preamp, then you displace resonance at rx tank you could get too much or too less voltage at preamp input thus getting saturation in first case or not enough signal in the path if amplification is fixed.

Kind regards,
Max

[Max]

Max: to answer his question, first can you tell us why choose Rx coil inductance at 6.2 mH, since with .015u capacitor gives resonance at 16.5 kHz while oscillator is around 14.5 kHz?

I never understand why not choose resonance at oscillator freq.

Regards,

-SB

Hi,
tgs is not full-resonant machine: means you don't need that tx and rx tanks will be on same resonant frequency. It isn't, and will never work on tgs.

The fact is that you need this setup to be sure you get the right phase shift and residual voltage required to other stages.

In full-resonant designs there are big issues about stability: think e.g. that you need a perfectly stable oscillator (any drift will alter the resonance and be amplified giving you troubles).... need a perfectly stable rx tank, same reasons... a cap change and you see that as sensitivity loss or false signal.... so fully-resonant tx-rx mds are very rare things, most of them are past stuff.

You'll actually see other approaches that avoid full-resonance like different order resonance like in some white's classic coil/md: there you have a fundamental osc frequency and rx tank is tuned on harmonic freq...

But now I see Qiaozhi already explained everything before me!

Kind regards,
Max

[Max]

Yes you are right. I need to study this more.

So maybe RX tank resonant freq is a critical factor we should pay more attention to and do fine adjustments with capacitor, not just rely on coil inductances.

Question is: what is best RX tank resonant freq and why?

Regards,

-SB

Hi,
it's a question to make at Tesoro's guys not here....

No... to be more serious... that frequency is the frequency at which you have maximum performances, still acceptable soil response/effects and less troubles means good disc, few false signals from iron-like stuff when in disc-mode....

But which frequency ?

Reality is that , as Qiaozhi stated, they use a compromise so don't even try to tune coils to the best they can but to "safe" operations, means rock solid disc and acceptable performance.

Some will observe that these Tesoro's md/coils in original made pieces are not so good...compared to other stuff, and that's right often.

That's why they wanna stay far from troubles: that's why we can put a tgs to the limit cause you can push one much but there's a limit.

Going through the limit means that you have fantastic perfomance on the bench but start losing disc accurancy and most important you'll easy overload and saturate machine when on real soil. Also you'll add a lot of instability in general, cause everytime you wanna push to the limit you'll go to amplify smaller and smaller voltage variations and that's a fact this give you instability... for many reasons not only soil effects or statics, but also e.g. near power lines etc

In all simple mds a top-sensitive unit will be top-sensitive to noise also.

Kind regards,
Max

[metaldetector107]

please help

Dear Max and other
1-i need the the exact frequency value for TX and RX
2- the best inductance value for TX and RX

and no more

best regards