IGSL

[simonbaker]

Minor update on my IGSL build, I am able to "null" my coils to a Rx coil pick of 0.4 mVolts (measured across the coil), YES 0.4mVolts measured on my scope.......Checked about 4 times to make sure that I was not misreading the scope display.....

The coils are just sitting in my Plywood search head, not even glued in, they need only a tiny movement to get down so low (the plywood head was made using Don's excellent TGSL 101 pdf, as were the coils)......

Also, that was measured in my Kitchen, with plenty of "Electrical interference" around, which is strongly believed to "interfere with sensitivity".......not exactly the best place I feel to make such a test.....

That's a lot less that the 4mVolts (factor x10) that Don talks about in TGSL 101......naturally gluing may eventually send it off, but has anyone else ever achieved such a low value? Is it normal? (thanks to anyone who replies with details).

I am NOT trying to say that its because of the way that I run my Faraday Shield wiring, or the cable type that I use, though, I am just happy that its that sensitive and I feel that that bodes well for the future.

Though it is one of the points that I sincerely believe that accurate/correct grounding of the shields helps. But absolutely no proof whatsoever as to if that is true or not, but it's good building practice.....

I am waiting to see what levels other people are achieving under the same circumstances, maybe mine is just quite normal......or even higher than really good machines.

Silverdog & Ivconic, what do you get as a null voltage measured on the Rx coil.....???

Sadly, I put my CD4024 chip in backwards(), blew it up, so I cannot progress further till that is replaced....next week!!

I need to make the head better looking before I glue the coils in anyway, so its not a problem really, plenty to do......just aggravating.....

Regards

Andy

mikebg would very much like your small null voltage because it allows more "headroom" for bigger preamp gain.

However, IGSL/TGSL preamp gain is fixed, so smaller null not helpful for that reason.

Such a small null is nice, but may not be important for good detection here. It may be that the effects of your shields and cable happen to cancel each other, or something like that. Or maybe it is due to a better cable/grounding arrangement -- to your credit -- something that would be nice to prove.

An ultra-small null may not improve anything because the motion detector circuit ignores the null anyway.

However, if your smaller null means smaller modulation of the signal by ground effects (ferrite), that could be important. That would require testing and comparing to a similar coil head with a larger null.

Because the overall null signal may be a combination of "magnetic" and "non-magnetic" couplings, it's hard to know often when we have found the smallest "magnetic" coupling point, which is what I think we want. Ivconic's practical testing with ferrite, targets, etc. seems like the best way to find that point.

Don't be shy to post photos of your work-in-progress. I'm the king of ugly, so it all looks good to me!

Regards,

-sB

[der_fisherman]

IGSL Null voltage....

There is moment when i reach "null" readings (0.00mV) at my millivoltmeter. I do have scope, but also prefer rather to use millivoltmeter for coils balancing, kind a habit.
So, there is a moment... but pretty soon voltage changes and usually stays in range 4-15mV.
I don't rely only on such readings, more i rely on air tests with hotrock, ferrite rod, various coins, ceramic etc..etc..
Before applying filler i perform such tests and correct a bit coil position, if needed. And it usually end up in range 4-15mV.
Funny, because original TS1000 coil is giving me 0.00mV when measured?!
Yet my 4-15mV coil is working same good as TS1000!?
In the past i insisted to fix null exactly to 0.00mV, but later such coils didn't performed so good!?
I think i know the reason of such difference between home made and original.
I always shield my coils with Al foil, while original TS1000 is shielded with graphite powder mixed with filler.
Al foil "mass" presence in coils vicinity is causing that 4-15mV jitter and seems it is quite normal for such setup.

I use Alumium foil too......that cannot be the only difference......

I will one day make a coil without Mylar, Alufoil or the like, I will only use copper wire wound at say 5 mm spacing.

If you look at the Faraday's cages used in many applications, there is more air than shield. Many are just an open metal mesh........

I feel that that will work well, especially for the Tx coil......more "power out"....

I wonder what that will do with the null, especially when both coils are made like that?

Problem is that its a lot of work, just to find out that its a rubbish idea!!!

Regards

Andy

[simonbaker]

I use Alumium foil too......that cannot be the only difference......

I will one day make a coil without Mylar, Alufoil or the like, I will only use copper wire wound at say 5 mm spacing.

If you look at the Faraday's cages used in many applications, there is more air than shield. Many are just an open metal mesh........

I feel that that will work well, especially for the Tx coil......more "power out"....

I wonder what that will do with the null, especially when both coils are made like that?

Problem is that its a lot of work, just to find out that its a rubbish idea!!!

Regards

Andy

Yes, try it, doesn't sound too hard to do if I understand.

I have a bottle of graphite waiting to be mixed with glue to make a potting/shield arrangement to get rid of the foil shield.

I keep wondering how important the TX shield is at all -- everyone insists it is, and I'm sure it is. But would be interesting to know when it is useful, how much difference it makes, and what does the shield actually accomplish technically (I've heard many theories I'd like to substantiate).

-SB

[der_fisherman]

Yes, try it, doesn't sound too hard to do if I understand.

I have a bottle of graphite waiting to be mixed with glue to make a potting/shield arrangement to get rid of the foil shield.

I keep wondering how important the TX shield is at all -- everyone insists it is, and I'm sure it is. But would be interesting to know when it is useful, how much difference it makes, and what does the shield actually accomplish technically (I've heard many theories I'd like to substantiate).

-SB

I would also be interested to know too.......

[Qiaozhi]

I waited all that time and it says the same thing a X then nothing.
Anyone whos sucessfully downloaded this rar file can they please just put it on here its only 5.2mb so should be easy.
Many thanks in advance
Dave

You cannot post it here, as it is cracked software.
Check your email.

[Jerry]

Before applying filler i perform such tests and correct a bit coil position, if needed. And it usually end up in range 4-15mV.
Funny, because original TS1000 coil is giving me 0.00mV when measured?!
Yet my 4-15mV coil is working same good as TS1000!?
In the past i insisted to fix null exactly to 0.00mV, but later such coils didn't performed so good!?
I think i know the reason of such difference between home made and original.

Here are the results of some experimenting on phase vs coil null voltages last year. I only did this on one coil so I should probably repeat it sometime to see if the results agree.

You can see that as the null voltage drops towards zero the phase shift increases.

These reading were taken with the coils pushed further together from the zero null point.

Next time I do this I am going to show a complete curve for both inside and outside of the null point.

Jerry

[Dennis the Mennis]

Here are the results of some experimenting on phase vs coil null voltages last year. I only did this on one coil so I should probably repeat it sometime to see if the results agree.

You can see that as the null voltage drops towards zero the phase shift increases.

These reading were taken with the coils pushed further together from the zero null point.

Next time I do this I am going to show a complete curve for both inside and outside of the null point.

Jerry

Hi Jerry ,


Great graph , wouldn't it be also very nice and interesting to display in this graph the source voltages of the Fet's ( TGSL : U C15 & U C12 ) in relation to the Shift and 'Nulling voltage ' ?

What did you use for shielding and what kind of cable did you use ? Just to get picture complete ...

kind regards ,

Dennis the Mennis

[Jerry]

Hi Jerry ,


Great graph , wouldn't it be also very nice and interesting to display in this graph the source voltages of the Fet's ( TGSL : U C15 & U C12 ) in relation to the Shift and 'Nulling voltage ' ?

What did you use for shielding and what kind of cable did you use ? Just to get picture complete ...

kind regards ,

Dennis the Mennis

Good point. I did not think of that. Will give that a try the next time. This coil had aluminum foil for shielding and a USB cable. I got excellent results with it but will use mylar on the next one. The foil I used was pretty thick.

When I posted this last year, I was hoping to get others to make the same test to see if these relationships hold for different coil sizes and shapes. When I do it again I will post more complete information.

You have given me some good ideas.

Thanks.

Jerry

[Wiltran]

IGSL

Good point. I did not think of that. Will give that a try the next time. This coil had aluminum foil for shielding and a USB cable. I got excellent results with it but will use mylar on the next one. The foil I used was pretty thick.

When I posted this last year, I was hoping to get others to make the same test to see if these relationships hold for different coil sizes and shapes. When I do it again I will post more complete information.

You have given me some good ideas.

Thanks.

Jerry

Interesting graph Jerry, thanks. This is one that been puzzling me. Does nulling your coils to the minimum voltage represent the optimum coil location for good depth, and discrimination? or do you then move the coils again slightly to another location for best operation. I'm hearing different opinions from others on this board. Some say null for best ferrite rejection! PS, Ive been using a usb cable which was what I thought had pretty good results. Now Ivconic and others are recommending Belden cable. Does anyone know what application Belden cable is usually used for? Sometimes knowing this make it easier to obtain at cheaper prices. Like audio cables, mike cables etc.

[ivconic]

Here are the results of some experimenting on phase vs coil null voltages last year. I only did this on one coil so I should probably repeat it sometime to see if the results agree.

You can see that as the null voltage drops towards zero the phase shift increases.

These reading were taken with the coils pushed further together from the zero null point.

Next time I do this I am going to show a complete curve for both inside and outside of the null point.

Jerry

Interesting graph!
In some way it justify my expectations.

[der_fisherman]

Interesting graph!
In some way it justify my expectations.

Hi Ivconic,

before I set my coils in Epoxy resin, may I ask if you have written already a "setup procedure" for both the IGSL Coils and the electronics? If yes, can you point that out to me, or a weblink.

All I have at this time is the setup for a TGSL from Don (which is really good, but does it apply to IGSL?), that I find too different, or I simply don't understand the similarities to be of any use for a IGSL.....

Thanks for your time and trouble.

Regards

Andy

[ivconic]

"....for a TGSL from Don (which is really good, but does it apply to IGSL?).."

Yes it does.

[der_fisherman]

"....for a TGSL from Don (which is really good, but does it apply to IGSL?).."

Yes it does.

Thanks.

[simonbaker]

Here are the results of some experimenting on phase vs coil null voltages last year. I only did this on one coil so I should probably repeat it sometime to see if the results agree.

You can see that as the null voltage drops towards zero the phase shift increases.

These reading were taken with the coils pushed further together from the zero null point.

Next time I do this I am going to show a complete curve for both inside and outside of the null point.

Jerry

That is food for thought. It makes me question my theory that the null signal is a pure magnetically coupled signal added to a non-magnetically coupled signal which is 90 deg out of phase with the TX signal.

For comparison, below is a graph of voltage vs phase when you sum a signal with another one that is 90 degrees offset.

I chose .4 mV PP for the size of the small signal that is 90 deg shifted. The signal at zero deg phase I varied in PP magnitude from 0 to 30 mV. I thought this might be typical of the coil Jerry was playing with.

My theory has been that the RX null signal consists of a variable (depending on position of coils) signal that is 0 or 180 degrees relative to the TX signal, added to a small "non-magnetically" coupled signal that is constant but approx 90 degrees relative to the TX signal.

Notice how my graph is "steeper" than Jerry's measured data. This suggests the null phase may be more complex than the sum of a variable signal plus a constant signal. Or could some scaling factor explain it?

I will keep thinking about possible models that might produce a more shallow curve like Jerry's data.

-SB

[der_fisherman]

"....for a TGSL from Don (which is really good, but does it apply to IGSL?).."

Yes it does.

Gentlemen,

I need your help.

I asked recently for a setup procedure for the IGSL and was told that the TGSL version will do it!!! That must be the most missleading comment that has ever been placed on any of Geotech's pages.

It may be that if you have also first built and setup a TGSL, that an IGSL is just a step up, no big deal, but I have never Built a TGSL, so I do not have this experience and knowledge.

If we compare the two a little maybe it will become clearer for those of you WITH THE KNOWLEDGE!

TGSL EDU Vers.4 has 3 pots or trimmers (I could not tell from the schematic as they were only marked as "R", not as "P" or "Tr"......) and a switch ( Disc on or off) as controls and setups.

Now let us look at the IGSL, it has generally 4 Pots and 5 trimmers (or 6 pots and 3 trimmers depending upon how you build it!!)

Furthermore the component makie up is quite different for test points - there is no 101 chip on an IGSL!!! For example.

There is simply no way that I can apply TGSL setup infos to an IGSL.

Also, there is no info on the schematic as to which side of any pot or trimmer needs to be the side with low resistance when turned fully anticlockwise, this means that if I get it the wrong way round,I will be turning the pot in the wrong direction for the setup (because the person that will write the setup will have some knowledge allowing him to connect the pots correctly....and I won't know what I am doing wrong!!!!!

I am assuming that the SilverDog PCB has got the trimmers orientated correctly, am I right or wrong on that point?) or could that be a further problem?

I am sure that I am not alone.....and what about future builders as many will be attracted to this obviously excellent design.....

Therefore I am appealing to the "IGSL knowledgeable" people to help me and others by posting a step by step method of setting up the IGSL, (IGSL for Dummies?)
with no reference to any TGSL material. Also detailing the Potentiometer's correct orientation as well....thanks in advance.

Regards

Andy

PS. My IGSL has not made any sort of "PEEP" yet, no matter what I turn and twiddle!! I am gradually working through the schematic, and up to now, I have not found any errors of build, but up to now, everything appears to be completely correct, voltages are fine,
signals can be seen...... I think its just that pots and trimmers are not setup....

Also there are strong debates for and against a good null!! WHO AM I TO BELIEVE, HOW SHOULD I SET IT UP?

We have so many variables, it's no wonder it hasn't made a sound.... (by the way Silverdog, that was a loudspeaker that I was not sure about the identification of, that you kindly supplied in the Kit?)