IGSL

[Pompey]

As I am not a Russian expert, it would be very nice if youcould write a few lines about how it works/is used etc..
Thanks in advance
Andy

It works very simlpy: "к частотомеру" means "to frequency meter" ,power suply 12V ,I think it works from 3 to 12 v and above.Frequency readings are the same.How to use: At the ends of resistor 22ohms you must connect two probes.Disconnect power suply from your PCB,but don`t disconnect tx and rx coils.(Tx can be disconnected -never mind)Connect power 12volt to coil generator ,connect two wires to frequency meter and with two probes (from ends of 22ohms) connect to the ends of the Rx(with resonant cap connected).Readins of the frequency meter is with difference from 1 to 5 herz maximum.Frequency of Tx measure with frequency meter and connected power on PCB.Rx -with generator and disconnected power on PCB!

[der_fisherman]

It works very simlpy: "к частотомеру" means "to frequency meter" ,power suply 12V ,I think it works from 3 to 12 v and above.Frequency readings are the same.How to use: At the ends of resistor 22ohms you must connect two probes.Disconnect power suply from your PCB,but don`t disconnect tx and rx coils.(Tx can be disconnected -never mind)Connect power 12volt to coil generator ,connect two wires to frequency meter and with two probes (from ends of 22ohms) connect to the ends of the Rx(with resonant cap connected).Readins of the frequency meter is with difference from 1 to 5 herz maximum.Frequency of Tx measure with frequency meter and connected power on PCB.Rx -with generator and disconnected power on PCB!

Many thanks
Regards
Andy

[hugo]

@Golfnut :
Ivconic tried in the past to use a Minelab coil with the Tesoro oscillator and he failed.
It can't works with such a low inductance.
That's the reason of this second schematic.

[golfnut]

I see thanx hugo


Steve

[golfnut]

Tx mods

In order to get more H field into the ground I took a look at the oscillator last night.

The one with 2 caps C1,C2 for IGSL coil.


In the model L1 has 30 mA pk flowing back and forth. 8v rail on the osc.

I tried 12v in model and peak I was 45mA in the coil.


So I did the mod on my unit and 'no noticeable' change, also it was more difficult to tune up and use.

I did not measure the residual nulled level with the extra power. I did measure the Tx frequency whilst on 12volts either. If I get time soon Ill revisit and post.

Steve

[bernte_one]

thank you guys
very friendly to help me

i use the shematic from igsl musketeer - the part that hugo posted

i have only confused the 1,2 differency between rx and tx- like supposed

will try the right specs an caps tonight if the were here in my toolbox
it must work

thx

[Jerry]

Dfbowers said the following in post #343:

"I never did figure it out. I just used the oscillator from the SMW project. But.. I was just doing a breadboard. They are almost alike except for a 2n2 capacitor replaces the 390K resistor (R4). Other than that, it's the same configuration with different resistor values.

Don "

Hope this helps.

Jerry

[golfnut]

I dont wish to confuse people. I barely understand it myself!

But, here goes...

The Transmitted signal that gets into the Rx (when over a target - due to upset null) is always the Transmitted signal frequency!.


The Rx pick up coil is resonant but - OFFSET by approx 1 or 2kHz. The signal getting into the Rx circuitry is still the same frequency that left the Tx coil. The level of signal getting into the Rx is reduced by the OFFSET in Rx frontend frequency.


I am uncllear what would happen if you tuned the Rx coil - 'onto channel'

I suspect your nulling would have to be better, any takers?

S

[Jerry]

I

I am uncllear what would happen if you tuned the Rx coil - 'onto channel'

I suspect your nulling would have to be better, any takers?

S

I think that the amount off offset was found by experimentation and is a compromise between sensitivity and stability.

The closer you bring the rx coil resonance to the transmitter frequency, the more sensitive the circuit will become but at the same time it will become more and more unstable.

I have experimented with this a little and that seems to be the case.

Jerry

[der_fisherman]

IGSL Stuff

In order to get more H field into the ground I took a look at the oscillator last night.
The one with 2 caps C1,C2 for IGSL coil.
In the model L1 has 30 mA pk flowing back and forth. 8v rail on the osc.
I tried 12v in model and peak I was 45mA in the coil.
So I did the mod on my unit and 'no noticeable' change, also it was more difficult to tune up and use.
I did not measure the residual nulled level with the extra power. I did measure the Tx frequency whilst on 12volts either. If I get time soon Ill revisit and post.
Steve

I read a lot here on Geotech (sadly I don't understand everything as well as I would like to!), but if I remember correctly, you need to increase the power through the Tx coil 64 times, to just double the receive power.....eg.not worth doing it, its more important to not empty your battery too quickly....

It would appear that refining the circuitry from the Rx coil is the only practical way to go....with that as a theme, what I would like to see eventually for the IGSL (probably could be adapted for other MDs), is a 50 or 60 Hz notch filter for when working near or underneath power lines.....I would expect that two filters would be required, one per channel. It would also make it easier to set up in a house or near power wiring etc.......

Once I have won the battle with my IGSL, I want to first add a VDI display to it as Ivconic said it was possible and that it worked, maybe one that can be switched in and out as wanted as someone else mentioned......

But mine has got to work correctly first, so I am considering a new coil using a Mylar Blanket instead of silver foil......The problem is that no matter what I do with the present coil, the ferrous channel sounds as good as never, no matter what is waved at the coil or how the trimmers and pots are adjusted......

The non-ferrous channel works quite well, depending of course upon how I set up the coils overlap, 30 cm on my wedding ring for example, but I still haven't fully understood the nulling lead/lag quite, even though I am using a 2 channel scope. Maybe because my coil is simply not good enough...

I also haven't finalised my battery power, nor the stem.....though I have an idea for the stem that I am hoping to try out in the near future. I am basing this idea on a crutch with a plastic top, and two alumium tubes, one sliding inside the other, its just a pig trying to find a plastic tube that fits the upper tube and is stiff enough. I am experimenting with PET at this time. If it doesn't work out, I will buy a stem from Georgi......

I was recently looking at an old design of VLF and it had several different caps that you could link in to get the Rx signal working best......maybe we should do something similar.....

I also have had a simple idea for a DIY Capacitor (variable) box....if anyone is interested, I could make a simple diagram......to help setting up both the Tx & the Rx.

regards

Andy

[simonbaker]

I dont wish to confuse people. I barely understand it myself!

But, here goes...

The Transmitted signal that gets into the Rx (when over a target - due to upset null) is always the Transmitted signal frequency!.


The Rx pick up coil is resonant but - OFFSET by approx 1 or 2kHz. The signal getting into the Rx circuitry is still the same frequency that left the Tx coil. The level of signal getting into the Rx is reduced by the OFFSET in Rx frontend frequency.


I am uncllear what would happen if you tuned the Rx coil - 'onto channel'

I suspect your nulling would have to be better, any takers?

S

This is an interesting design idea (which I hope to try), but requires a number of changes to make it work. You can't do it successfully with the existing TGSL/IGSL design by just changing your RX resonant frequency. But it may be fun to try to see what it does.

With the existing design, on-resonance RX will radically shift all the target phases so your DISC and GB pot won't work right. Also, it will raise the gain of the received (and null) signal a lot and probably overload the system.

In addition, it makes a very "unstable" design, meaning that slight component variations that affect the TX oscillator frequency or RX resonant frequency will make big variations in the target phases.

However, it may have some advantages also if you can overcome the difficulties, so worth looking into!

I used a capacitor bank to test varying the RX resonant frequency (or you can vary the oscillator frequency) for experiments. I found that "on resonance" never worked, but you could actually get some performance by making the TX oscillator frequency higher than the RX resonant frequency instead of lower -- i.e. off-resonance on the high side. It was not excellent, but worked -- maybe could have been improved. I doubt it has any big possibilities, but don't know.

-SB

[bernte_one]

thank you guys
very friendly to help me

i use the shematic from igsl musketeer - the part that hugo posted

i have only confused the 1,2 differency between rx and tx- like supposed

will try the right specs an caps tonight if the were here in my toolbox
it must work

thx

ok i have tryed this 2 minutes ago

it does not work with my excelerator 2 coil
the null voltage i measure is every time 2,6 volt (thats to high) i hear sinus signal at headphone continuous when i turn trimmers on one little point so the oszilator is working i think

but coil gives signal when metal object is sweeping over no maybe it is not nulled like the normal coils we know???

next days i order a original 4pin tesoro or other minelab - i have laying around a supersearch with 1mH and 20mH i will give it a try before

or maybe back to diy coil :-( (so much work but prooven)

[golfnut]

All, just had a play with my igsl (I have the Tx osc on the 12v rail).


I did a range check on a UK pound coin = 1 length of A4 paper for detect (absolute limit) 29cm.
My osc was on 14.5kHz


Tweaking the osc base bias pot also tweaks the frequency of Tx a liitle too - I altered the pot.

The collector ac rms volts only moved down by a 200mV, 9.1Vrms to 8.9Vrms - so no appreciable power change, but..

at 14kHz the range was now approaching half the distance.


If this is good science and you suffer range, try to get your Tx freq checked.

If you have a counter with a sensitive input, coil up the test leads and offer up to the coil of your completed IGSL - that way the measurement wont Pull it off freq during the mment.

In the state I left it I can more reliably reject ferrous and none ferrous targets, the pots seem to do what u expect.

S

[golfnut]

Where I left the unit, I mean I put it back on 14.5KHz

S

[bernte_one]

could be my solution...

maybe it is better to calculate by myself
here my result


what do you mean