IGSL

[golfnut]

I know metal detectors and radios are not the same thing but the idea is the same.

Hi Jerry, they are one and the same.

The Rx is a zero or low IF type, our target signals after the mixer/sychronous detector - reside at anywhere from 0 to 15Hz and is dependant on shaft length and the demeanor of the operator!

Ive done some club digs in the UK with 80 people in a line up with a shotgun start - the front runners will cut you in half with their mad hacking slash and fully extended units.

It would be real neat to get a sig gen on these units to get a real number for performance - rather than where we are now.

It may be possible to take a sniff of the Tx coil signal, buffer it to provide isolation, add some FM somehow, attenuate to uV range and wire to Rx input.

If your Tx was derived from a xtal you could use a quality synthesised signal 9Hz above or below to give an IF signal in the Filter bandwidth.

Or maybe a VCO phase locked to your Tx with Audio tone as a modulation input to FM it and feed that to RX.


If the Rx sig was simply phase shifted from the Tx (which it isnt its frequency shifted also i.e. more than a cycle of shift) you could have put the Tx signal down a roll of coax to get a phase shifted signal for the Rx, or another RC delay.

S

[zoomix]

Raisonance RX IGSL

anglais


français


arabe



Alpha

hello,

Ok but why give this value of 16.1khz on RX as a "reference"?

and according to the formula F0 = 159 / (R (6500X15000)) = 0.01610Mhz = 16.1Khz

I also see that many people have posed the same question on the forum.

I'' ve made the PCB Edwardian controlled by ivonic. I see no more q'uil zener diode, on the part BC327 TX ... more components are missing compared to the first version ..

Is what else is done with it functional iGSL PCB? May be an error or correction would have efcaped

Thank you to you

[Qiaozhi]

Looks like I have no Raisonnance on RX since I measure the same frequency.

This is a common misconception. The RX frequency will always measure the same as the TX frequency, even if the RX coil is not in resonance. It will just have a lower amplitude.

[golfnut]

Does 15 nf of RX must necessarily be done with 2 capacity?

If you need 15 and you have 15 fit a single cap.

S

[zoomix]

IGSL trouble RX

français


anglais


arabe



Alph
Hello,

I modified C2 (22n) by 19.7nf and my frequency can be set exactly on 14.6khz TX.

Looks like I have no Raisonnance on RX since I measure the same frequency.

For nulling, I made the measure recommended by DFbowers, tell me if it's good because there are several methods and several values that are spread all over the net.


TX-coil connected
I disconnected the 2 wire of the RX coil
I measure the terminals of this coil RX with DVM(range 200mv AC).

(induction of TX and RX gives me a voltage to these terminals)
coupling I did allow me to measure AC 4mV

I mean 4 milivolts .... is this correct?

the result is good, I have to dis and I eliminate the ferrite with GB.

But I did not 16.1khz on RX....

Does 15 nf of RX must necessarily be done with 2 capacity?
I have 1cap of 15 nF and i see a post that show a diagram of RX with 2 cap necessarily

Merci

a

[o.mag]

hi all
Would somebody has tested igsl with a 15 " coil of relic hawk

olivier

[ivconic]

This is probably the cause of your problem. The value of 4mV to 15mV is what you would expect to see across the RX coil, not at the output of the pre-amp.

Yes i am thinking the same.

[Qiaozhi]

The adjustment of the coils is made ("nulling"). I have 4 to 15 mV without problem on pin 1 of LM883.

This is probably the cause of your problem. The value of 4mV to 15mV is what you would expect to see across the RX coil, not at the output of the pre-amp.

[Jerry]

I think you're saying: let's measure a reference gain (at some frequency) through the filter/amp sections (i.e, after the synchronous detector JFets) to the output of the LM308s, just to have it handy for quick checking.

Sounds useful and easy, 10 Hz is a reasonable choice. We can also easily check it with LTSpice and see how well it matches your measurements.

-SB

Hi Simon,

Yes that is what I was saying. When I built my second TGSL, the performance was way down and the problem turned out that I mis-read the color code multiplier for 4.7K resistors and installed 47K in their place. I tracked down the problem by comparing overall gain from the Detector JFets to the LM308 outputs with my first TGSL.

Since I already had a good working unit, it was a simple matter to compare the two but for a first time builder I can see where it would come in handy for trouble shooting.

Jerry

[ivconic]

Hi all,

I finished with my IGSL shielded coils as in the tutorial
TX = 6,127 mH
RX = 6.55mH

I put the pot directly into GB 10k front for easy adjustment on site.

The resistors 1.5M are replaced by 470k and condos in 10nF by 22nF (ceramic)

The adjustment of the coils is made ("nulling"). I have 4 to 15 mV without problem on pin 1 of LM883. My coils are not yet cast in epoxy. They are attached to the hot melt adhesive.


By setting a bit, I get 25 30 cm on a 1 euro coin

Here is my function:

After looking around and min / max of potentiometers, I realize that discrimination does not remove ferrous.

I must say that I get lost a bit so I worked on it. The sounds serious ferrous and non-ferrous acute.

1) When I remove the ferrite with the GB, There is almost no régalge possible. the device is limited in adjustment or is saturated.

2) When I activate the ferrous discriminiatiion to 20%, I eliminate the 1 euro coin but not ferrous. when Barrng is 100%, a small block of iron is not discriminated.

I visualized the oscilloscope to pin 13 of Cd4066 and compared with the image of the manual TGSL Don bowers (TR4 block 5) and the signal is not clean. It is tripled or quadrupled on the rising edges.

The TX signal is clean and the output P1 of U4A to pin4 also own ..
I did not-but-6.2volt 6volt ... and +8.1 volts at the output of Lm7808

Can you advise? replace the 4066 or perform test and measurement?


3) I 14.15 Khz Max on TX and I RX on the same frequency. while

According to the manual TGSL 101 & 102, I should have 16.1Khz in resonance with 15nF and RX.

Is what I should adjust C1 and C2?

4) As I said, the coil is not cast in resin but it is fixed in the disk. When I touch the disk or cable, there are interferences ... is this normal?

Thank you for your help

"...TX = 6,127 mH RX = 6.55mH.."

I think that might be a problem.
6mH/6.5mH should do. Or ~5.6mH/~6.2mH as at original Tesoro coils.

"...I have 4 to 15 mV without problem on pin 1 of LM883..."

Maybe a slightly undernulled?

Yes; 16.1-16.2kHz is calculated RX frequency.
It is off resonance setup because TX should run on approx 14.2-14.6kHz.
Don't know what to suggest; looks like it is about coil.

[zoomix]

IGSL setting

Hi all,

I finished with my IGSL shielded coils as in the tutorial
TX = 6,127 mH
RX = 6.55mH

I put the pot directly into GB 10k front for easy adjustment on site.

The resistors 1.5M are replaced by 470k and condos in 10nF by 22nF (ceramic)

The adjustment of the coils is made ("nulling"). I have 4 to 15 mV without problem on pin 1 of LM883. My coils are not yet cast in epoxy. They are attached to the hot melt adhesive.


By setting a bit, I get 25 30 cm on a 1 euro coin

Here is my function:

After looking around and min / max of potentiometers, I realize that discrimination does not remove ferrous.

I must say that I get lost a bit so I worked on it. The sounds serious ferrous and non-ferrous acute.

1) When I remove the ferrite with the GB, There is almost no régalge possible. the device is limited in adjustment or is saturated.

2) When I activate the ferrous discriminiatiion to 20%, I eliminate the 1 euro coin but not ferrous. when Barrng is 100%, a small block of iron is not discriminated.

I visualized the oscilloscope to pin 13 of Cd4066 and compared with the image of the manual TGSL Don bowers (TR4 block 5) and the signal is not clean. It is tripled or quadrupled on the rising edges.

The TX signal is clean and the output P1 of U4A to pin4 also own ..
I did not-but-6.2volt 6volt ... and +8.1 volts at the output of Lm7808

Can you advise? replace the 4066 or perform test and measurement?


3) I 14.15 Khz Max on TX and I RX on the same frequency. while

According to the manual TGSL 101 & 102, I should have 16.1Khz in resonance with 15nF and RX.

Is what I should adjust C1 and C2?

4) As I said, the coil is not cast in resin but it is fixed in the disk. When I touch the disk or cable, there are interferences ... is this normal?

Thank you for your help

[simonbaker]

I was trouble shooting my a TGSL about a month ago and wound up injecting a 10 hz signal into the filter stages at the source of Tr4 and Tr5 and looking at the outputs of the LM308's. Once I got the problem fixed, the input sensitivity was about 25uV for .6Vpp at the 308's which was a huge improvement from original.

By "the Disc sens setting at 3mV at maximum sensitivity", are you refering to the output of the gain stages with 6 uV input?


I think having input sensitivity specs for a given output of the gain stages is good to have for determining how well the circuit is working. Sort of like a two way radio tech measuring .1 uV at the antenna connector for 20 db of quieting in a receiver. I know metal detectors and radios are not the same thing but the idea is the same.

Right now I have a same of two units to make comparisons on.

It looks like you are have a lot of success with your IGSL.

Jerry

I think you're saying: let's measure a reference gain (at some frequency) through the filter/amp sections (i.e, after the synchronous detector JFets) to the output of the LM308s, just to have it handy for quick checking.

Sounds useful and easy, 10 Hz is a reasonable choice. We can also easily check it with LTSpice and see how well it matches your measurements.

-SB

[Davor]

By "the Disc sens setting at 3mV at maximum sensitivity", are you refering to the output of the gain stages with 6 uV input?

Actually I was referring to each of the gain stages in IGSL. I was not referring to the total sensitivity, because it depends somewhat upon the discrimination setting. You can add the preamp gain (~33dB) and subtract the switchers loss (~13dB), and correct it for discrimination angle ... too much to do. Say, frontend voltge multiplication is 10 and just apply target angle correction factor of ~0.5, with 6µVpp sensitivity of each of the gain stages, you get ~0.5µVRMS total sensitivity.

There is not much difference in TGSL either, except that TGSL gain stages have a bias problem due to bipolar opamps use. LM358 in this particular configuration will pull output of the gain stage 10-20mV below gnd, while the minimum criterion for the comparators to trigger is +3mV (maximum sensitivity). With TGSLs biasing problem total sensitivity falls to ~2µVRMS vs 0.5µVRMS in IGSL. Hence, to gain over 10 db sensitivity in TGSL, you only have to go for FET input opamps with low input bias current instead of LM358, just like IGSL does. At maximum sensitivity you enjoy more of the silence, while I enjoy more of depth and some chatter, and it both happens with the same +3mV comparators threshold.

BTW, I put TL064 instead of LF347, and it goes a bit more into the + side.

You can try with TL062. Prepare for a bit of amazement.

[simonbaker]

Yeah, I get good depth even with wrong GEB I just didn't leave enough margin to account for highly mineralised soil: red soil soaked in sea salt. I couldn't get anything from the sea though - my GEB pot with poor margins didn't reach it. Waving a coil over the sea without a real ground balance produced a very funny series of tones.

Be assured that I noticed chatter already, and I know what you are referring to. I get it too when a car with bad electricity passes by, but I can wipe it off by adjusting Disc sense - in effect I am trading sensitivity for noiseless operation. I guess the original antichatter would wipe off small signals too because it is too slow in recovering. I get chatter, but it is a manageable nuisance.

There are two cures for EMI that I can think of.

Electronics tinkering way around this would be a noise blanker, but it would require either a tuned tank with high Q (impractical) or a delay line to be effective. Once I modded the old FT101 SW transceiver's noise blanker and got miraculous results. Can you imagine - they've put a diode in reverse so the original blanker never worked

The other would require a modified, differential coil, where Rx coil resembles figure 8 of a sort. There is a phasing problem with this approach, but not so much if Tx is running a differential coil too. This will have to be further examined. The idea is that differential coils are much more sensitive to the local signal than the far field, so in effect they are cancelling EMI. Guitar pickups are typically differential coils, so they don't pick up hum, ergo Humbucker pickups.

Yes, I've played a little with figure-8 type RX with centered TX; Aziz using "top hat" stacked coils; they should have potential against EMI -- not needed out in the wilderness. Another technique against EMI should be increasing TX power. I've played a little with resonant TX coil in that regard. All take much more experimenting.

-SB

[Jerry]

The whole chain of channel gain stages (without preamp) has sensitivity at ~6µVpp set by the Disc sens setting at 3mV at maximum sensitivity.

I was trouble shooting my a TGSL about a month ago and wound up injecting a 10 hz signal into the filter stages at the source of Tr4 and Tr5 and looking at the outputs of the LM308's. Once I got the problem fixed, the input sensitivity was about 25uV for .6Vpp at the 308's which was a huge improvement from original.

By "the Disc sens setting at 3mV at maximum sensitivity", are you refering to the output of the gain stages with 6 uV input?


I think having input sensitivity specs for a given output of the gain stages is good to have for determining how well the circuit is working. Sort of like a two way radio tech measuring .1 uV at the antenna connector for 20 db of quieting in a receiver. I know metal detectors and radios are not the same thing but the idea is the same.

Right now I have a same of two units to make comparisons on.

It looks like you are have a lot of success with your IGSL.

Jerry