TGSL Tuning & troubleshooting

[simonbaker]

I attach teoretical scope pic. I am 99% sure i will see the same on the scope.

Also i attach one more lower - yours real oscilograms, posted on page 57. I made from your pics, it will help to compare.

So mine impulses are shifted 90 degrees from yours. This will change polarity, not shape.
Why equal 90? I am so good to ballance coil 90 degrees from yours? Not 12 or 47 ? Think no. Reason is somewhere else.

Hi johnsmith77:

LF353 pin 7 is not a good reference for phase. Can you do same pics but referenced to TX signal?

Sometimes a 90 deg shift means wrong capacitor somewhere -- uF instead of pF -- for example.

But first let's compare waveforms referenced to TX signal.

Regards,

-SB

[johnsmith77]

I don't have 2 channel scope. Will try with 2 channel pc scope, so signal shape will not be very nice with that kind scope at almost at the end of 20khz (sound card), but phase shift can be obtained

I attach teoretical scope pic. I am 99% sure i will see the same on the scope.

Also i attach one more lower - yours real oscilograms, posted on page 57. I made from your pics, it will help to compare.

So mine impulses are shifted 90 degrees from yours. This will change polarity, not shape.
Why equal 90? I am so good to ballance coil 90 degrees from yours? Not 12 or 47 ? Think no. Reason is somewhere else.

[simonbaker]

I don't have 2 channel scope. Will try with 2 channel pc scope, so signal shape will not be very nice with that kind scope at almost at the end of 20khz (sound card), but phase shift can be obtained

We'll see -- maybe too much frequency/phase distortion, but worth a try.

-SB

[johnsmith77]

Hi johnsmith77:

I think silver should not be rejected at 5. Maybe more like 10.

I am interested in seeing the oscilloscope traces comparing the TX oscillator (J1-1) to the gates of TR4 and TR5 at different pot positions (DISC pot for TR4 gate, GB pot for TR5 gate).

Put pot at 0, 5, 10 and show each pair of traces.

Regards,

-SB

I don't have 2 channel scope. Will try with 2 channel pc scope, so signal shape will not be very nice with that kind scope at almost at the end of 20khz (sound card), but phase shift can be obtained

[simonbaker]

I have pot leads reversed, but i know it and when i say min, it is on pot max really. So there is no difference. I later change them. It is my mistake, which generally not effect tgsl working. It would affect i did not know it

It should be: CCW by mine opinion to R19, 3,3k; CW to R17, 100K

Foil, silver is rejected about at 5. Later check more.

I add some picture. It would help better compare to yours.

Hi johnsmith77:

I think silver should not be rejected at 5. Maybe more like 10.

I am interested in seeing the oscilloscope traces comparing the TX oscillator (J1-1) to the gates of TR4 and TR5 at different pot positions (DISC pot for TR4 gate, GB pot for TR5 gate).

Put pot at 0, 5, 10 and show each pair of traces.

Regards,

-SB

[johnsmith77]

Another pic.

[johnsmith77]

Hi johnsmith77:

It would help if your links referred to the message containing the photo instead of the photo itself. Then we can see the context.

I'm not sure, but it may be possible that your coils are nulled to a different phase, which could make the oscilloscope signal at tr4 drain look different. It depends on which side of the minimum null point you choose. However, which side you choose null should not affect the basic DISC function. The target signal phase is the same regardless of null signal phase.

Are you sure you do not have the DISC pot leads reversed? Please describe more fully how your DISC control is working. For example, for each pot position, list all the metals that are rejected and which metals are accepted. Describe which position is clockwise (CW) and which is counter-clockwise (CCW). For example, some people divide the pot range from 0 to 10, with 0 meaning fully CCW.

Regards,

-SB

I have pot leads reversed, but i know it and when i say min, it is on pot max really. So there is no difference. I later change them. It is my mistake, which generally not effect tgsl working. It would affect i did not know it

It should be: CCW by mine opinion to R19, 3,3k; CW to R17, 100K

Foil, silver is rejected about at 5. Later check more.

I add some picture. It would help better compare to yours.

[simonbaker]

So in TGSL_101 documentation i found usb cable connection: J2-1 (U101a pin 5 not inverted) goes to ground in coil head.
In forum i see (also your posts) J2-2, should go to ground in coil head.

Is there a mistake in that manual or in forum?

I think that is definitely a mistake in the illustration -- good catch! We should fix that since it seems pretty essential. As dfbowers mentioned, the alternative wiring (with no grounding of RX coil) removes the possibility of error.

This highlights how darn difficult it is in these forums to divine a clear, accurate set of instructions for building some of these projects. Reading the threads is fraught with peril -- every other post has a mistake or disagreement. It really is an experimenter's game here. But Don's and Ivconic's manuals are the gold standard for now. It is very important to put such documents in a "sticky" post, like Qiaozhi did with Ivconic's material, and then allow continual editing to fix discovered errors. That way over time the information will become more thoroughly "vetted", tested, and reliable, and you'll always know where to find the latest version.

Of course if you're willing to tinker, analyze, and ask questions, you'll eventually get there regardless.

-SB

[simonbaker]

Mistake on tgsl 101 pdf. As i described in upper post.

But on TR4 drain pin (disc channel) i see negative impulses. Yours positive: http://http://www.geotech1.com/forums/attachment.php?attachmentid=3277&stc=1&d=119294976 3


And TR5 drain pin (gb channel positive impulses). Yours negative: http://www.geotech1.com/forums/attac...1&d=1192949787

According to your oscilograms it should be on contrary.


Reasons?:
Coils gives no double beeps sound, so not reversed rx or tx. Wrong phase shift with 29cm 1e detection and good ferrite rejection?
Even try a big and small off ressonance: add plus 1nf parrallel to RXc or to TXc. Later plus 10nf to RXc or to TXc. Just for trying to make another phase shift, to check if i can get other polarities.
I could not make signals at these points sinus shape opposite polarity. Can get only if signal shape rectangle, but it means nulling bad.

Thanks

Hi johnsmith77:

It would help if your links referred to the message containing the photo instead of the photo itself. Then we can see the context.

I'm not sure, but it may be possible that your coils are nulled to a different phase, which could make the oscilloscope signal at tr4 drain look different. It depends on which side of the minimum null point you choose. However, which side you choose null should not affect the basic DISC function. The target signal phase is the same regardless of null signal phase.

Are you sure you do not have the DISC pot leads reversed? Please describe more fully how your DISC control is working. For example, for each pot position, list all the metals that are rejected and which metals are accepted. Describe which position is clockwise (CW) and which is counter-clockwise (CCW). For example, some people divide the pot range from 0 to 10, with 0 meaning fully CCW.

Regards,

-SB

[johnsmith77]

Hmm.. I don't know why I didn't notice that before. Maybe a mistake in the TGSL_101 document. To check, only connect shields in coil to the cable shield.
That's the only way I have been building them lately and it improves performance in wet grass.

But this don't change Tr4, Tr5 drain signal polarities in mine TGSL. Another mistake in ?http://www.geotech1.com/forums/showt...hase#post61260

pictures F11-F17.

Can't still clear up.

Sorry for that, but have suspect that oscilograms F11-F17 was made with mixed scope leads: ground to signal, signal to ground.
Or rx, maybye tx leads reversed during scopping.
It is important to me, cause i want be sure i made TGSL correctly or not.

[dfbowers]

I checked trim, pots, switch connections, it is ok.

On TR4 drain pin (disc channel) i see negative impulses.
And TR5 drain pin (gb channel positive impulses).

According to oscilograms in forum it shoul be on contrary.

So in TGSL_101 documentation i found usb cable connection: J2-1 (U101a pin 5 not inverted) goes to ground in coil head.
In forum i see (also your posts) J2-2, should go to ground in coil head.

Is there a mistake in that manual or in forum?


Thanks

Hmm.. I don't know why I didn't notice that before. Maybe a mistake in the TGSL_101 document. To check, only connect shields in coil to the cable shield.
That's the only way I have been building them lately and it improves performance in wet grass.

[johnsmith77]

Can you try to describe it more fully? I'm not clear what is happening.

As Ivconic answered once, it is possible to wire the DISC or GB pots backwards, so they work in opposite rotation from what you expect.

Please describe it more fully.

Regards,

-SB

Mistake on tgsl 101 pdf. As i described in upper post.

But on TR4 drain pin (disc channel) i see negative impulses. Yours positive: http://http://www.geotech1.com/forums/attachment.php?attachmentid=3277&stc=1&d=119294976 3


And TR5 drain pin (gb channel positive impulses). Yours negative: http://www.geotech1.com/forums/attac...1&d=1192949787

According to your oscilograms it should be on contrary.


Reasons?:
Coils gives no double beeps sound, so not reversed rx or tx. Wrong phase shift with 29cm 1e detection and good ferrite rejection?
Even try a big and small off ressonance: add plus 1nf parrallel to RXc or to TXc. Later plus 10nf to RXc or to TXc. Just for trying to make another phase shift, to check if i can get other polarities.
I could not make signals at these points sinus shape opposite polarity. Can get only if signal shape rectangle, but it means nulling bad.

Thanks

[johnsmith77]

Can you try to describe it more fully? I'm not clear what is happening.

As Ivconic answered once, it is possible to wire the DISC or GB pots backwards, so they work in opposite rotation from what you expect.

Please describe it more fully.

Regards,

-SB

I checked trim, pots, switch connections, it is ok.

On TR4 drain pin (disc channel) i see negative impulses.
And TR5 drain pin (gb channel positive impulses).

According to oscilograms in forum it shoul be on contrary.

So in TGSL_101 documentation i found usb cable connection: J2-1 (U101a pin 5 not inverted) goes to ground in coil head.
In forum i see (also your posts) J2-2, should go to ground in coil head.

Is there a mistake in that manual or in forum?


Thanks

[simonbaker]

Sorry, not have.
Furthermore, discrimination works only by one metal. If reject foil, then accept iron and contrary. If reject silver, than accept iron, foil, etc.

Can you try to describe it more fully? I'm not clear what is happening.

As Ivconic answered once, it is possible to wire the DISC or GB pots backwards, so they work in opposite rotation from what you expect.

Please describe it more fully.

Regards,

-SB

[ivconic]