RX coil and sensibility

[waltr]

Hi Waltr,
thanks for the advice; tomorrow will be a beautiful day so I can try it in the garden. As for the three questions I can only tell you that in DISC mode rejects the nails in AM mode sees them.For the other two tests (silver / ferrite and nichel) I'll try.In recent days I thought that the neon light could disturb and so I worked without light but maybe not enough.
Thank you for everything and have a good week.
Tony60.

Another test to try.
Measure the Vpp of the outputs of U104 & 105 but put a Short across the RX input at C6. If the Noise at U104, 105 drops to ~5-10mVpp then you know the coil is picking up electrical noise and your circuit is working fine.
I just checked this and noise went from ~50mVpp to under 5mVpp when shorted C6.

There are so many item that produce electrical noise. Almost ALL of the wall-warts (AC to DC power bricks) run switching PS at 10's of kHz. Also computers and monitors put out lots of noise.

If this test results in low noise at U104, 105 then you MUST get the TGSL outside away fro electrical noise to evaluate detection distance.

Lets us know how this test goes.

[Tony60]

Well Waltr,
this is a very unteresting test that tomorrow I will definitely try before going to try in the garden.
As soon as I try, I'm going to displease you right away.
Thank you and good night.
Tony60.

[Tony60]

Good morning Waltr,
as you suggested I tried measure the noise with the RX coil short but the values have not changed; in the afternoon I'll try to take him out then we'll see.
Thank you and have a good week
Tony60.

[waltr]

Ok, that seems to indicate the Noise is within the circuit.

What are you using to power the TGSL? A battery is best.

[Tony60]

Ok Waltr,
I use a traditional power supply (not switching) but I can certainly try it with battery,GREATTIP.I will run a test outdoors and with battery.
Thank you again.
Ciao Tony60.

[dbanner]

By "traditional power supply" you mean a regulated bench supply? There might be some ripple on the output.

[waltr]

By "traditional power supply" you mean a regulated bench supply? There might be some ripple on the output.

Correct and it could be coupling noise, higher frequency, from other devices on the AC mains into the TGSL.

[Tony60]

Hello Waltr in the afternoon I tried outside with the battery but not changed anything, I am disheartened...sic. In thread "TGSL EDU mod" at msg #1 and #8 I found a mod, can you tell me what you think ??
Thank you and good afternoon.
Tony60.

[waltr]

Guessing this thread: https://www.geotech1.com/forums/showthread.php?22412-TGSL-EDU-Mod

These mods are ok IF the detector is working reasonably well but will NOT fix noise or distance issues.
At best it may add a few cm distance to a circuit that is already working well.

Did you re-measure the noise at the outputs of U104 & 105 while shorting the RX input (C6) and powered from a battery?

If the noise at these two op-amp outputs is too high then you will not get good detection distance.
Shorting the RX input removes any effects due to the coil. Do be sure to make a very short jumper across C6.
No I think it is this thread:
https://www.geotech1.com/forums/showthread.php?21579-TGSL-EDU-Mod

The front end mod may help you a little but if there is still noise at U104,105 with C6 shorted then probably will not help.

I left everything as designed first. Now that I feel my build is working well I plan on these mods but will do them one at a time to ensure it didn't make it worse.

[waltr]

Tony,
I am not trying to discourage you but the TGSL is not the easiest to get working when you build your own coils.
https://www.geotech1.com/forums/show...tivity-deepnes

This is only one of many threads/posts with the same issue you have.

Even the TGSL I just built does not have the depth other have obtained BUT I have been using it and I like how it works since I have found a number of good finds without digging rusty nails.

I have also spend many, many hours reading all the threads here on the TGSL and many people have trouble getting good distance.
Please keep fiddling and reading. Once it seems to work ok then time to build another coil, I am planning to build more coils to try and obtain the distance other get.

[dbanner]

Now I read above you stated noise at U104/105. Make sure polarities of C14a/b and C17a/b are correct if you did not use bipolar caps.
Stay away from using ceramics caps around these sections of schem. Use PP.

[Tony60]

Dear Waltr,
thenk you for your words of courage and help you and other friends. This morning I still performed a noise measurement in these conditions: battery 12.1V RX input on short, neon, router and cellulars on off but nothing has changed; I would like to try to replace LM308 TL070 I don't know.
Thank you for all and good evening.
Tony.

[Tony60]

Hello Dbanner,
thank you for your interest. For these components I used counterpolarized electrolytic capacitors.
Have a good evening.
Tony60

[Tony60]

Excuse me Waltr,
for the this morning measurements I have two pictures; scope are setting 50mV/div - 10uS.

[dbanner]

That looks like a rapidly decaying pulse.