TGSL Tuning & troubleshooting

[golfnut]

more powerful oscillators

All I was sharing ideas with Maurice on here recently...

Ive a few complimentary mos pair ICs from model moter speed controller, I have been itching to give them a try - just finished working out a way of getting the original IGSL oscillator (which is reliable and good) up to 1A pk to pk. Decent harmonics at -40dBc too

Maybe a bit too lively - but good acedemic exercise all the same.

Steve

[golfnut]

Hmm I cant open this Ill try 1 more time.

S

[golfnut]

If this file wont simulate - save it as a new file name first then run the sim.

May just be my machine not simming the download.

S

[simonbaker]

Hmm I cant open this Ill try 1 more time.

S

Looks very nice, similar to experiments habitbraker and I were playing with. http://www.geotech1.com/forums/showp...&postcount=356

I wonder if it is a little difficult to get L2 and L3 with those low resistance values.

Also the low inductance of L2 implies fewer coil turns, and since magnetic field is proportional to current * turns (I think??), are we really getting as much bigger field as we think even though the voltage/current is a lot higher? Probably something we need to calculate, the magnetic field for these high-voltage coils.

Also watch out for phase shift across your "dropper" divider circuit. Not much, but little things can add up...

I like it! Hope you build it and show us some experments.

-SB

[satdaveuk]

Hi satdaveuk:

First, what kind of factory coil? D-D or concentric? What size?

Did you say using lower capacitors you got a higher TX frequency? That sounds backwards, but maybe you meant same caps but different coil.

I have always believed that the relationship of RX resonant freq to TX oscillator freq is more important than actual values. But there may be another factor. If you have local noise sources that are right at 14.67 kHz, then dropping the TX oscillator can be a good way to dodge the noise.

Changing the TX freq without changing the RX resonant freq will slightly change the gain, and even more slightly change the phase shift.

Raising the TX freq should increase the gain, so that could also be why you hear more chatter.

But then wouldn't we expect better depth with more gain (you ask)??? Yes, except noise is a total bugger (pretending I'm a Brit) with the TGSL and can very efficiently reduce depth -- it seems to be due to the final "noise gate" filter just before the audio section.

Whether increased gain can actually reduce depth due to the "chatter filter" effect I'm not sure. But certainly if your TX frequency goes nearer to a noise frequency, you'll pick up more noise and get less depth.

Makes me think that maybe we should consider "tunable" oscillators for our TGSL MDs so we can evade certain noise sources.

Regards,

-SB

I cant really give the reasons Simon, soon as time permits I will do more tests the way it is and keep you informed, you say nearer to a noise frequency well maybe your correct, but in that case other builders here should be getting it also, as I said tests were done outside although in a built up location, in practise if that is the problem it takes me back to thinking rather than filtering out frequencys why not just drop the operating frequency and consontrate on uping the gain.

Im not as technical as you Simon but with the TX/RX the less CX the higher the frequency and by adding capacitance was lowering the frequency that was all done with a 8" brown round Tesro coil which would normaly be purchased with the TGS.
Thats why I always go a little above frequency because its easer to add caps for the final tweek than having to start subtracting.
Please tell me im right on this otherwise im totaly confused and going bonkers

[satdaveuk]

All I was sharing ideas with Maurice on here recently...

Ive a few complimentary mos pair ICs from model moter speed controller, I have been itching to give them a try - just finished working out a way of getting the original IGSL oscillator (which is reliable and good) up to 1A pk to pk. Decent harmonics at -40dBc too

Maybe a bit too lively - but good acedemic exercise all the same.

Steve

You certainly got your 1A goal ill give you that golfnut, looking forward to the results when you built it
Will the standard coils handle it 1A ok? know doubt you have considered that, far as battery life etc I shouldnt worry about it at the moment lets just see if your circuit has worth while end results.
All the best

[simonbaker]

I cant really give the reasons Simon, soon as time permits I will do more tests the way it is and keep you informed, you say nearer to a noise frequency well maybe your correct, but in that case other builders here should be getting it also, as I said tests were done outside although in a built up location, in practise if that is the problem it takes me back to thinking rather than filtering out frequencys why not just drop the operating frequency and consontrate on uping the gain.

Im not as technical as you Simon but with the TX/RX the less CX the higher the frequency and by adding capacitance was lowering the frequency that was all done with a 8" brown round Tesro coil which would normaly be purchased with the TGS.
Thats why I always go a little above frequency because its easer to add caps for the final tweek than having to start subtracting.
Please tell me im right on this otherwise im totaly confused and going bonkers

No you are correct, I had dyslexia and thought lower meant bigger in my mind, so yes, smaller caps increases freq, sorry for confusion. Makes good sense to start with small cap and tweak upwards.

I think that 8" Tesoro coil is a concentric -- which doesn't matter much if you did both tests with same coil, again I was addled and thought maybe you switched coils and got less depth, but I guess you just tweaked the cap using same coil.

So... not clear why less depth with higher freq, but interesting to note. Let us know if you find out more.

I wish I could do lots of tuning tests for max depth, but so much noise in workshop that it is futile. I need to get a portable scope I can take into the field.

Cheers,

-SB

[satdaveuk]

No problem we all get confused from time to time its are old age creepng on use lol thought you may of mixed up with inductance which as you know is reverse.
Anyway couple of things firstly due to me doing most tests on the main board with the manufacture tesro coil my CX values need to be different than Ivionics circuit values because im running different inductances so my values are: TX=5.7mh total of both series capacitors need to be 21nf which= 14.546khz the easest way is dig into both bags of 220nf/20nf pick the lowest values stick them in circuit which will proberly take you higher frequency than required then make the difference by slaping say a 820pf across the two.
Far as the RX you need 17nf which will give you 16.168khz, I had a stamped 15nf which was reading 15.5nf paralled a 1.5nf and it got me there, I think im right in saying a few herz one way or the other wont matter just dont venture over the 100hz-200hz.
Simon havent put this down so much for your benifits because I know you would work this out with a drop of the hat, its mainly for the novis whos making a kit up with bought ready made tesro coils.
Saying all that im still not convinced that these frequencys are the best for these circuites but its earlys days and alot more tests need to be done.
Also not discounted the idea of pushing my coil tester oscillator through it yet to try and give it extra clout, thats something else on to do list when time allows.

My final thing is im sure someone my have tryed this but if not certainly one for the simulator and go from there.
Someone has said on here more than once thats its not so much the inductance of coils its the frequency split which is say 14.5khz- TX 16.1KHZ RX which = 1.6khz difference,
So I have quite a few 6mh coils due to cock ups etc in the early days, if we were to introduce CX of 220nf+22nf in series as per circuit that gives me 20nf which = 14.528KHZ so we know thats the TX sorted, now with another 6.0mh coil and applie 16.2nf across the coil that gives a reading of 16.143khz which would be the RX.
The question is in theory it should work or maybe not, but in practise will it? If it will what are the draw backs because there always is, and if it was that easy why dont the manufactures do it, possably a good question for Carl or Mike.
Anyway hope Ive not tread on old ground and bored you all
Warm regards

[der_fisherman]

Changes and Ideas.....

I cant really give the reasons Simon, soon as time permits I will do more tests the way it is and keep you informed, you say nearer to a noise frequency well maybe your correct, but in that case other builders here should be getting it also, as I said tests were done outside although in a built up location, in practise if that is the problem it takes me back to thinking rather than filtering out frequencys why not just drop the operating frequency and consontrate on uping the gain.

Im not as technical as you Simon but with the TX/RX the less CX the higher the frequency and by adding capacitance was lowering the frequency that was all done with a 8" brown round Tesro coil which would normaly be purchased with the TGS.
Thats why I always go a little above frequency because its easer to add caps for the final tweek than having to start subtracting.
Please tell me im right on this otherwise im totaly confused and going bonkers

Has anyone here even given any thought to possible radio transmitter harmonics (some submarine transmitrters are VLF as well, see here:-
http://en.wikipedia.org/wiki/Communi...ith_submarines
They talk of between 3 and 30KHz) causing noise and loss of sensitivity in VLF metal detectors? That might be an explanation why some people (in one area for example) have better luck with other frequencies, than someone in another area.....

What is needed is a Rx coil attached to a sensitive frequency display ( a small unit attached to say a PC with software to display the results and at what frequency?) that shows just what frequencies are received say between 0 and 20 Khz.....(probably a smaller bandwidth would actually do)......then turn on the Tx oscillator and watch where it peaks. Add or remove caps till it peaks in a "clean" area......same for the Rx coil of course....

Then maybe it might be a good idea to have a selector switch for different caps for the Rx & Tx circuits so that you can select a different working frequency depending upon where you are.

The next is to adapt the code for the VDI to allow displaying of such interference at the search site......plus a switch to turn the Tx coil on and off......while receiving still.....(it must be a tiny graphic display LCD, not just blocks!)

Just some ideas to have our experts think about, but don't shoot me down too hard if you think I'm really off track, but I am hoping that someone can pick up and refine the ideas.....

It might need to be a small separate portable unit rather than adding weight to the metal detector.

I have also read somewhere that PI detectors can suffer from radio interference.....

Let me down gently Guys.

Happy new year everybody.

regards

Andy

[simonbaker]

No problem we all get confused from time to time its are old age creepng on use lol thought you may of mixed up with inductance which as you know is reverse.
Anyway couple of things firstly due to me doing most tests on the main board with the manufacture tesro coil my CX values need to be different than Ivionics circuit values because im running different inductances so my values are: TX=5.7mh total of both series capacitors need to be 21nf which= 14.546khz the easest way is dig into both bags of 220nf/20nf pick the lowest values stick them in circuit which will proberly take you higher frequency than required then make the difference by slaping say a 820pf across the two.
Far as the RX you need 17nf which will give you 16.168khz, I had a stamped 15nf which was reading 15.5nf paralled a 1.5nf and it got me there, I think im right in saying a few herz one way or the other wont matter just dont venture over the 100hz-200hz.
Simon havent put this down so much for your benifits because I know you would work this out with a drop of the hat, its mainly for the novis whos making a kit up with bought ready made tesro coils.
Saying all that im still not convinced that these frequencys are the best for these circuites but its earlys days and alot more tests need to be done.
Also not discounted the idea of pushing my coil tester oscillator through it yet to try and give it extra clout, thats something else on to do list when time allows.

My final thing is im sure someone my have tryed this but if not certainly one for the simulator and go from there.
Someone has said on here more than once thats its not so much the inductance of coils its the frequency split which is say 14.5khz- TX 16.1KHZ RX which = 1.6khz difference,
So I have quite a few 6mh coils due to cock ups etc in the early days, if we were to introduce CX of 220nf+22nf in series as per circuit that gives me 20nf which = 14.528KHZ so we know thats the TX sorted, now with another 6.0mh coil and applie 16.2nf across the coil that gives a reading of 16.143khz which would be the RX.
The question is in theory it should work or maybe not, but in practise will it? If it will what are the draw backs because there always is, and if it was that easy why dont the manufactures do it, possably a good question for Carl or Mike.
Anyway hope Ive not tread on old ground and bored you all
Warm regards

In theory seems it should work fine. If not, I would like to know why.

It would certainly take the pressure off winding coils with extreme exactitude, and probably many builders here already tune their MDs that way.

We already know that the IGSL works fine with very different coils, the standard TGS coil and the Muskateer style coil, so that kind of proves the point I think.

A good point to make. But if there is a subtle difference that makes some coil inductance values optimal, we have another interesting subject to flog within an inch of its life.

One subtlety is the coil resistance, which can affect the "Q" of the RX tank, and possibly some stability/phase issues. Also the TX coil resistance affects battery drain probably.

Cheers,

-SB

[simonbaker]

Has anyone here even given any thought to possible radio transmitter harmonics (some submarine transmitrters are VLF as well, see here:-
http://en.wikipedia.org/wiki/Communi...ith_submarines
They talk of between 3 and 30KHz) causing noise and loss of sensitivity in VLF metal detectors? That might be an explanation why some people (in one area for example) have better luck with other frequencies, than someone in another area.....

What is needed is a Rx coil attached to a sensitive frequency display ( a small unit attached to say a PC with software to display the results and at what frequency?) that shows just what frequencies are received say between 0 and 20 Khz.....(probably a smaller bandwidth would actually do)......then turn on the Tx oscillator and watch where it peaks. Add or remove caps till it peaks in a "clean" area......same for the Rx coil of course....

Then maybe it might be a good idea to have a selector switch for different caps for the Rx & Tx circuits so that you can select a different working frequency depending upon where you are.

The next is to adapt the code for the VDI to allow displaying of such interference at the search site......plus a switch to turn the Tx coil on and off......while receiving still.....(it must be a tiny graphic display LCD, not just blocks!)

Just some ideas to have our experts think about, but don't shoot me down too hard if you think I'm really off track, but I am hoping that someone can pick up and refine the ideas.....

It might need to be a small separate portable unit rather than adding weight to the metal detector.

I have also read somewhere that PI detectors can suffer from radio interference.....

Let me down gently Guys.

Happy new year everybody.

regards

Andy

Very nice feature to consider.

In the future our MDs will have "scanners" to look for clear frequencies and hop there automatically!

-SB

[Farside]

I'm building a IGSL-TGSL right now and once my standard coils are made and everything is working as it should, I intend to modify the Tx and Rx frequencies exactly as you propose.

I used this calculator to work out the necessary capacitor values (especially the Tx Colpitts oscillator):
http://www.zen22142.zen.co.uk/Theory/tunedcct.htm

I was thinking about why 1.6KHz was specifically chosen as a delta between Tx and Rx. why not 1KHz or 1.5KHz?
I then realised that 1.6 is a close approximation to the golden ratio (1.61 and I suspect this was the original motivation for choosing this number.
If I'm correct then the golden ratio has been mis-applied IMHO. I am intending to apply it correctly.

Now the golden ratio delta for 14.5 KHz is 8.96 KHz which seems way too big of a frequency difference to me. However, the golden ratio is fractal in nature and I noticed that the 4th order golden ratio (1.6 of 1.6 of 1.6 of 1.6) is 2.116KHz and a 5th order is 1.308KHz.

I'm personally choosing the 4th order because the 4th order pops up a lot in 3 dimensional mathematics (like electromagnetics of 3D space:
http://www.physlink.com/education/askexperts/ae174.cfm)

Maybe you think I'm a bit loopy... but here is an interesting link about the orders of the golden ratio in nature:
http://jwilson.coe.uga.edu/emat6680/...fib_nature.htm

The 5th order looks promising also.

Anyway, I'm building the winding jig right now so I'll keep you posted once I'm ready to do the mods.

[simonbaker]

I'm building a IGSL-TGSL right now and once my standard coils are made and everything is working as it should, I intend to modify the Tx and Rx frequencies exactly as you propose.

I used this calculator to work out the necessary capacitor values (especially the Tx Colpitts oscillator):
http://www.zen22142.zen.co.uk/Theory/tunedcct.htm

I was thinking about why 1.6KHz was specifically chosen as a delta between Tx and Rx. why not 1KHz or 1.5KHz?
I then realised that 1.6 is a close approximation to the golden ratio (1.61 and I suspect this was the original motivation for choosing this number.
If I'm correct then the golden ratio has been mis-applied IMHO. I am intending to apply it correctly.

Now the golden ratio delta for 14.5 KHz is 8.96 KHz which seems way too big of a frequency difference to me. However, the golden ratio is fractal in nature and I noticed that the 4th order golden ratio (1.6 of 1.6 of 1.6 of 1.6) is 2.116KHz and a 5th order is 1.308KHz.

I'm personally choosing the 4th order because the 4th order pops up a lot in 3 dimensional mathematics (like electromagnetics of 3D space:
http://www.physlink.com/education/askexperts/ae174.cfm)

Maybe you think I'm a bit loopy... but here is an interesting link about the orders of the golden ratio in nature:
http://jwilson.coe.uga.edu/emat6680/...fib_nature.htm

The 5th order looks promising also.

Anyway, I'm building the winding jig right now so I'll keep you posted once I'm ready to do the mods.

I like your name, it says it all...

[Jerry]

I'm building a IGSL-TGSL right now and once my standard coils are made and everything is working as it should, I intend to modify the Tx and Rx frequencies exactly as you propose.

I used this calculator to work out the necessary capacitor values (especially the Tx Colpitts oscillator):
http://www.zen22142.zen.co.uk/Theory/tunedcct.htm

I was thinking about why 1.6KHz was specifically chosen as a delta between Tx and Rx. why not 1KHz or 1.5KHz?
I then realised that 1.6 is a close approximation to the golden ratio (1.61 and I suspect this was the original motivation for choosing this number.
If I'm correct then the golden ratio has been mis-applied IMHO. I am intending to apply it correctly.

Now the golden ratio delta for 14.5 KHz is 8.96 KHz which seems way too big of a frequency difference to me. However, the golden ratio is fractal in nature and I noticed that the 4th order golden ratio (1.6 of 1.6 of 1.6 of 1.6) is 2.116KHz and a 5th order is 1.308KHz.

I'm personally choosing the 4th order because the 4th order pops up a lot in 3 dimensional mathematics (like electromagnetics of 3D space:
http://www.physlink.com/education/askexperts/ae174.cfm)

Maybe you think I'm a bit loopy... but here is an interesting link about the orders of the golden ratio in nature:
http://jwilson.coe.uga.edu/emat6680/...fib_nature.htm

The 5th order looks promising also.

Anyway, I'm building the winding jig right now so I'll keep you posted once I'm ready to do the mods.

I do not think too much should be read into the 1.6 Khz offset. This has been found to work by experimentation and other offsets work well also. The receiver will get more sensitive as you move resonance closer to the TX however it also gets much more unstable as you move closer. Move too far and you loose too much sensitivity so 1.6 Khz or thereabouts seems to be a good compromise. Picture the Rx resonance point being located x Db down on the skirt of the transmitter selectivity curve.

I see the temptation to compare with the "Golden Ratio" since it is a number used pretty much everywhere. However, I think in this case it is a happy coincidence.

But it is fun playing around with the numbers.

Looking forward to seeing your results.

Jerry

[golfnut]

As the Tx oscillator is the Rx Local oscillator - or a direct conversion Rx.

The only Rx frequency available is that of the LO.


Offsetting the tuned front end further makes the Rx more deaf - like an off tune radio.


Id guess the selectivity of the coil / cap on these is fairly loose.. So we can blagg these offsets.

Again as stated, if the coil / cap was 'on channel', or peaked for reception on the Tx frequency, nulling would be more difficult for starters.

As mentioned, in use the chances of proximity effects pulling the Rx coil / cap AND the Tx / coil cap ---- by the exactt same amount are low.

Or another way to keep the two tuned circuits phase aligned to introduce no falsing is a little fanciful - unfortunately. Although nothings impossible right..

S