Question about tgsl

[waltr]

Dbowers has a file on his web site for coil template.
I did have to play with 'zoom' parameter in the 'print' dialog to get it the correct size.
I probably print three copies that size was not correct.

[waleed]

I used a frequency generator and it have frequency measurement feature, and the oscillator frequency did not change only RX frequency changed, I thought it will be 14.3khz as TX frequency but it was a little bit higher, anyway I want to ask what prototype did you use to build your coils, or you just made it yourself as the specifications?, because when I printed the one in the document the dimensions wasn't the same.

https://i.ibb.co/0KymDpT/Screenshot-20200225-191216-Drive.jpg

[waltr]

I have never made a concentric coil for the TGSL (only for a PI).

The frequency on the RX coil should be exactly the same as the TX. The RX would only be phase shifted.
What are you using the measure Frequency??
If the instrument 'loads' to connection (TX Oscillator) then it can Change the frequency of oscillation. This sounds like what might be happening.
Remember the Heisenberg Uncertainty principle and Observer Effect.

https://en.wikipedia.org/wiki/Observer_effect_(physics)

As shown in the TGSL 101.pdf it is best to always use two channels of Oscope. Ch1 always on TX oscillator and triggers scope.
Then Ch2 can be used to examine any other signal related to the TX waveform.

[waleed]

Also I connected both coils to the device, I measured at J1-1 the frequency was 14.3khz, and then I measured at J2-1 the frequency was 14.5khz is that normal? Shouldn't it be the same when I connect both coils?, waltr can you check yours and see if they are the same or not.

[waleed]

Do you mean the Vpp measurement?
Or the Scopes Volts per division scale?

You made me open the detector and put a Scope on it.
I have 50mVpp at the output on the RX pre-amp (u101a, pin 7), Scope on 50mV/div.
This means about 1mVpp output at the RX coil.

I do remember that my first coil was no where near this low and had a completely wrong phase but did work reasonable well. The GB and Disc worked and sensitivity was ok in field tests. I did find and dig many targets including some 15cm deep small coins.

If the RX amplitude is large to obtain the correct phase then the coil's inductance ratio (or the tuning Caps, C2 or C6) are not correct.

The second coil was built with a Double sided form like Dbowers uses and used the exact number of turns he stated (98 TX & 107 RX). I connected a mechanical turns counter so I didn't lose count. Also, applied polyurethane to the wire as I was winding so the coil come off the form 'glued' together so no constraining was required.
I used a Graphite powder mixed with polyurethane for Shielding. First coil was aluminum foil shield.

This second coil Nulled well with the correct phase shift. The final Null was done with a screw glued to the coil shell and the two coils epoxied in except for a 15cm length of one coil. This allowed a Very Fine final adjustment.

This second coil works very well in the field. Never sure if sensitivity (depth) is good since every target and ground condition is different. But I have dug a 1.5cm brass button from 25cm down that was nearly under an iron Ox shoe.

Thanks waltr you should have posted this long time ago ^^ ,I'll remake my coils same manner, I saw many people says that the difference between TX and RX is 5 turns, but do you remember how many turns did you use for the concentric 10"?,and the last thing that will really help,take a pic for TX and RX connecting them at oscillator tank,I mean connect the TX only put the oscilloscope on 5v/50us while monitoring on J1-1 then take a pic, after that connect the RX the same as TX and then take a pic, I just want to compare them with mine

[waltr]

Thanks guys your replies is always helpful to me, I will go to uni tomorrow and connect both TX and RX to the oscilloscope dual trace and check for the phase degree, waltr you said 1Vpp but what was the dev?

Sorry I meant voltage division*

Do you mean the Vpp measurement?
Or the Scopes Volts per division scale?

You made me open the detector and put a Scope on it.
I have 50mVpp at the output on the RX pre-amp (u101a, pin 7), Scope on 50mV/div.
This means about 1mVpp output at the RX coil.

I do remember that my first coil was no where near this low and had a completely wrong phase but did work reasonable well. The GB and Disc worked and sensitivity was ok in field tests. I did find and dig many targets including some 15cm deep small coins.

If the RX amplitude is large to obtain the correct phase then the coil's inductance ratio (or the tuning Caps, C2 or C6) are not correct.

The second coil was built with a Double sided form like Dbowers uses and used the exact number of turns he stated (98 TX & 107 RX). I connected a mechanical turns counter so I didn't lose count. Also, applied polyurethane to the wire as I was winding so the coil come off the form 'glued' together so no constraining was required.
I used a Graphite powder mixed with polyurethane for Shielding. First coil was aluminum foil shield.

This second coil Nulled well with the correct phase shift. The final Null was done with a screw glued to the coil shell and the two coils epoxied in except for a 15cm length of one coil. This allowed a Very Fine final adjustment.

This second coil works very well in the field. Never sure if sensitivity (depth) is good since every target and ground condition is different. But I have dug a 1.5cm brass button from 25cm down that was nearly under an iron Ox shoe.

[waleed]

??dev?? Please explain what this means.

Sorry I meant voltage division*

Also do remember that 0.1mm movement of one coil to the other can make a huge difference in phase.
It is a very touchy adjustment.

Yes I noticed that when I was adjusting the coils..

[waltr]

but what was the dev?

??dev?? Please explain what this means.

Also do remember that 0.1mm movement of one coil to the other can make a huge difference in phase.
It is a very touchy adjustment.

[waleed]

Thanks guys your replies is always helpful to me, I will go to uni tomorrow and connect both TX and RX to the oscilloscope dual trace and check for the phase degree, waltr you said 1Vpp but what was the dev?

[waltr]

I am trying to remember the Vpp out of the Pre-amp when I got a Null with the correct 20 degree phase shift. I think it was in the 1Vpp range which is perfectly fine.
If you have the correct phase shift at pre-amp out then 1.4Vpp is fine. When metal passes under the coil the amplitude of the RX signal does not change much (for normal 'good' targets) it is the Phase that changes for detection.

Ferrite rejection POT adjustment is very, very touchy. Move the pot too far and SILVER is rejected (not foil).
So use a small piece of ferrite and a silver coin to adjust the GB Pot, ferrite rejected and silver detected. This is done in All Metal Mode.

Then in DISC Mode, increasing the disc pot should reject a small piece of foil (about 1 cm square) then larger piece of foil as the pot is turned, then US Nickle & Pull-tabs.

A big problem comparing test results (your 25cm distance on A coin) is what coin??? The 1 Euro is a standard in Europe but not in the US.
The BEST Air Distance reported in the forum here is 35cm for a 1 Euro but 25cm is more typical. Also remember this is AIR tests which are very different distances than targets in the ground.

[Qiaozhi]

This is really weird, all the day I'm trying to get the lowest null but I couldn't, the deepest null that I could have reach is 1.4v at U101 pin7, I checked the frequency for both coils at uni using frequency meter connecting them at TX oscillator so TX was 14.3khz and RX 13.7khz, I can detect a coin about 25 cm but I couldn't reject the ferrite and foil, I'm confused because I have the correct difference between TX and RX frequency (0.6khz) but I can't reach a good nulling. The coil is not shielded yet also.

This is my 10" DD coil, I constrained them by glue and rounded them using electric tape.
https://i.ibb.co/x3KPG9D/20200224-152618.jpg

As Waltr said, you should not seek to get the lowest null. The important thing is to get the phase offset correct.

[waleed]

This is really weird, all the day I'm trying to get the lowest null but I couldn't, the deepest null that I could have reach is 1.4v at U101 pin7, I checked the frequency for both coils at uni using frequency meter connecting them at TX oscillator so TX was 14.3khz and RX 13.7khz, I can detect a coin about 25 cm but I couldn't reject the ferrite and foil, I'm confused because I have the correct difference between TX and RX frequency (0.6khz) but I can't reach a good nulling. The coil is not shielded yet also.

This is my 10" DD coil, I constrained them by glue and rounded them using electric tape.

https://i.ibb.co/x3KPG9D/20200224-152618.jpg

[waltr]

Waleed,
Sounds like the TGSL is working correctly.

Yes, never will get 4mV at output of pre-amp. Also, what is more important than minimum Vpp is the correct phase shift. The RX signal should be about 20 degrees after the TX. The puts the RX waveform at the correct delay for the DISC & GB samples.
Having the correct inductance difference between the RX & TX coils is important to obtain the 20 degree phase.

[Nandor]

In the Rx signal there is also noise that gets amplified! So you need more signal than noise this is signal to noise ratio. More good signal than noise means better sensibility to small and distant targets. Try at least 1-1.5Vpp to make at the output of you Rx than you will see improvement!

[Nandor]

Hey dont be sad, you need 4mv at the coil not at the output of the Rx amp At U101 you need about 1Vpp, read twice before doing something wrong