TGSL Experiments

[ivconic]

I'm inclined to try the piggyback approach and just add the new oscillator and Minelab coil to one of my existing TGSLs. I think that I can get away with just removing one resistor or adding a jumper to select between coils. I will let you know how I make out for sure. The only thing I can't do at the moment is vacuum form so I might be stuck with bench testing for a few weeks.. Simon, BTW.. are you on FB?
Don

That's really interesting idea! To have such versatile detector, to be able to switch between various coils and setups!
But you should project it very good indeed - to void certain side effects that may occur. Method of switching is very important.
Ordinary mechanical switches would not be most proper choice, may involve some stray capacitances, sparks, interferences, unwanted loops....etc...etc.
But idea is really good, so it is worth to be worked on it a bit more serious.
For a start just consider this:

http://eu.mouser.com/knowledge/vishay/vishaydgswitchesmux/

First task would be to cut down piggy pcb contacts to least possible number. Same to do with existing oscillator on main pcb. Than to choose most proper analogue switch (or few) by which those two oscillators will be switched.
Analogue switch must be placed pretty close to switching points (shortest possible tracks). "Com" inputs than can be connected with long tracks to front panel and tied up to mechanical switch.
This is feasible and real. I like it!

[simonbaker]

I'm inclined to try the piggyback approach and just add the new oscillator and Minelab coil to one of my existing TGSLs. I think that I can get away with just removing one resistor or adding a jumper to select between coils. I will let you know how I make out for sure. The only thing I can't do at the moment is vacuum form so I might be stuck with bench testing for a few weeks.. Simon, BTW.. are you on FB?
Don

Great, I'd like to hear what you think about comparing the two types of coils and oscillators (Minelab vs TGSL). Must be some reason they went to small TX and large RX coil inductance in later Tesoro models.

I would assume you need bigger oscillator caps with Minelab coil because smaller TX inductance???

Not sure why but I have avoided Facebook -- maybe just don't want to make that guy any richer!

Geotech is my main home, although I pop up occasionally with questions on other sites also..

-SB

[dfbowers]

Don: You're not supposed to jet ski and metal detect at the same time!

Hope the wrist heals smoothly. Very inconvenient I'm sure. Glad you escaped greater injury.

Smaller coil sounds like good fit for TGSL; easier to use also. I'll have to build a new coil form for one that size.

What do you think of the minelab coil for the IGSL that Ivconic retrofitted? Do you think it could work with TGSL oscillator, or does it require the minelab oscillator mod as well? Should we try that minelab coil and oscillator mod with TGSL? I'd like to see what the results might be.

Regards,

-SB

I'm inclined to try the piggyback approach and just add the new oscillator and Minelab coil to one of my existing TGSLs. I think that I can get away with just removing one resistor or adding a jumper to select between coils. I will let you know how I make out for sure. The only thing I can't do at the moment is vacuum form so I might be stuck with bench testing for a few weeks.. Simon, BTW.. are you on FB?
Don

[ivconic]

Hello,
I would like to buy and build the TGSL kit.
But before, I've got a question.
Can we imagine a piggyback pcb to "upgrade" Tesoro TX stage to Minelab Musketeer one ?
Ivconic already did it into his IGSL schematic !
With it, it can be possible to use a large range of coils available on the market.

Maybe, I'm completly wrong ! who knows ?

UPDATE : Hoops, Simonbaker is faster than me !

You are not wrong, it is ok, you can do that and later use some original Musketeer coil with TGSL too.

[hugo]

Tesoro to musketeer coil - TGSL

Hello,
I would like to buy and build the TGSL kit.
But before, I've got a question.
Can we imagine a piggyback pcb to "upgrade" Tesoro TX stage to Minelab Musketeer one ?
Ivconic already did it into his IGSL schematic !
With it, it can be possible to use a large range of coils available on the market.

Maybe, I'm completly wrong ! who knows ?

UPDATE : Hoops, Simonbaker is faster than me !

[simonbaker]

Well it looks like I'm out of the coil making business for a month or two. Jet ski accident and a busted wrist . Testing coils is going to drive me nuts with all the metal the doc had to add to my wrist to hold it together!! I can still swing a coil left handed and experiment with what I have .
Last two months I finished 2 more TGSLs and 3 more coils for the TGSL, an 8", 10" and now just for the heck of it, a 9" like I made for my Surfmaster PI Pro from Silverdog.

120 mm x 238mm for one "D". Tx= 106t Rx=111t with .25mm wire (came out to be 12oz with a complete epoxy fill. A 1e air tests at just about 30cm.

I took the 9" coil for a swing this evening . First impressions., a bit less noisy than the 10" and ground depths just about the same. The bigger coil seems to loose the "air test" advantage in hard packed clay ground. I was tempted to try an 11" DD coil but maybe reaching the point of diminishing returns for coins? I'm still going to go with Ivconics 10" coil as best overall. 9" coil is very usable though!!

Don

Don: You're not supposed to jet ski and metal detect at the same time!

Hope the wrist heals smoothly. Very inconvenient I'm sure. Glad you escaped greater injury.

Smaller coil sounds like good fit for TGSL; easier to use also. I'll have to build a new coil form for one that size.

What do you think of the minelab coil for the IGSL that Ivconic retrofitted? Do you think it could work with TGSL oscillator, or does it require the minelab oscillator mod as well? Should we try that minelab coil and oscillator mod with TGSL? I'd like to see what the results might be.

Regards,

-SB

[ivconic]

Better not post those images in the Remote Sensing forum. It might cause a lot of confusion.

[Qiaozhi]

I just like those "golden" coils!
Those will simply "suck" golden coins from a soil!

Better not post those images in the Remote Sensing forum. It might cause a lot of confusion.

[ivconic]

I just like those "golden" coils!
Those will simply "suck" golden coins from a soil!
Now serious: i really like those coils! Congratulations! Excellent work!

[dfbowers]

Your coils are looking good Don. I used the glossy black plastic thinking that less dirt would stick to it, but it gets dirty looking anyways. I noticed that you moved the coil cable down to the bottom of the coil. Did you have trouble balancing the coils when you had it next to the coil pivot point?

The 8" coil works great as well but there was a noticable difference in depth between 8" and 10". Maybe an inch or two. I really couldn't tell any difference between the 9" and 10".

"Widgetworks" sells the plastic with the "haircell" finish that tends to hide the scratches.

I actually like the cable exiting near the rod but with the strain reliefs I have been using it's just more convenient to form a small depression in the corner of one of the "D"s to accept the nut on the other side. I have wondered for a long time what difference it makes as to where the cable exits. I don't have any proof to support ideas one way or another. Or another good one is, Tx on top or Tx on the bottom? I'm still up in the air.

[Wiltran]

Dbower coils

Your coils are looking good Don. I used the glossy black plastic thinking that less dirt would stick to it, but it gets dirty looking anyways. I noticed that you moved the coil cable down to the bottom of the coil. Did you have trouble balancing the coils when you had it next to the coil pivot point?

[Jerry]

Sorry to hear about the wrist Don. I agree on the smaller sized coils. I had very good luck with the 8 inch DD that I made. My results is about the same as you reported. Now I just have to get some shells made but it has been way to hot to fire up that pizza oven.

Jerry

[dfbowers]

TGSL and coil size.

Well it looks like I'm out of the coil making business for a month or two. Jet ski accident and a busted wrist . Testing coils is going to drive me nuts with all the metal the doc had to add to my wrist to hold it together!! I can still swing a coil left handed and experiment with what I have .
Last two months I finished 2 more TGSLs and 3 more coils for the TGSL, an 8", 10" and now just for the heck of it, a 9" like I made for my Surfmaster PI Pro from Silverdog.

120 mm x 238mm for one "D". Tx= 106t Rx=111t with .25mm wire (came out to be 12oz with a complete epoxy fill. A 1e air tests at just about 30cm.

I took the 9" coil for a swing this evening . First impressions., a bit less noisy than the 10" and ground depths just about the same. The bigger coil seems to loose the "air test" advantage in hard packed clay ground. I was tempted to try an 11" DD coil but maybe reaching the point of diminishing returns for coins? I'm still going to go with Ivconics 10" coil as best overall. 9" coil is very usable though!!

Don

[simonbaker]

2 weeks

Out town for couple weeks, no posts!

[mikebg]

I have to think about that, it seems logical....

It should be OK for transistor to enter saturation during short pulse I would think, although perfect sine wave maybe optimal. So maybe that is where duty cycle comes in. A good point to think about.

I'm not too worried about distortion of TX signal because TGSL has big bump anyway as it is and can get good results! I think synchronous detector integrates out high frequency harmonics.

Regards,

-SB

Simon,
The problems of harmonics in TX field is not for synchronous demodulator, despite it sees them.
The main problem appears in preamp, because for maximal depth it should always give in output maximal voltage swing, near to distortion limits. Then it operates with maximal gain. The demodulator can not see this signal if it contains only the reference frequency. However a distorted by preamp signal contains not only ref. frequency.
Each unwanted signal in input:
AIR (induction disbalance),
GND (soil signal),
EMI (interference),
N (thermal noise),
forced us to reduce preamp gain in order to avoid distortion (intermodulation). Small gain of preamp means small depth. Note that a bad designed preamp circuit amplifies even mains frequency signal which at high gain causes intermodulation.