Question about tgsl

[waleed]

Yes I know, and to get the deepest null you should have the correct difference frequency between TX and RX, the most important thing that I learned is that you'll never reach the 4mv on the output of the preamp because of the gain, if you have a good nulling it will be like 300-400mv, and the 4mv you should achieve it on the end lead of the RX disconnect from the board, I think someone should modify the document because it say while monitoring on pin7 of U101 to reach 4mv and that is wrong, this is really important. Anyway I'm going now to the uni to see what I'll get..

[Ozoz_xba]

Hey waltr, check the video, I'm really surprised with the results, the LCR I bought I found that It needs to be calibrated, so after I calibrated it I measured the TX coil and it was 6.6mH, and then I made the RX coil it was 8.3mH (I know it's too high I'll adjust it later) and I didn't even constrain it yet, SO I just decided to attach it to the device and see how it would act (remember, RX coil still not constrained because I may remove some turns to get proper inductance) and then I turned the device on it gave a single beep as normal and it was so quiet, I just put the GB pot to the mid range and then moved a piece of ferrite and I overlapped the coils until the ferrite got rejected, after that I switched the disc switch to disc mod, so iron is rejected then I started to move the disc pot until foil is rejected (I just moved it a little bit not too much), the thing got me surprised with the result is that I'm pretty sure that RX inductance isn't correct and the coil is not constrained yet, I'll go to the uni tomorrow and make sure to get the 1.6kz difference between the two coils (by removing some turns from RX coil), I believe that the depth wasn't that good because the difference between TX and RX isn't 1.6kz and I also believe that the null wasn't perfect as well. I'll see tomorrow what will happen when I go to the uni and check everything.


https://youtu.be/cfXjZVju8Yw

If you dont have depth then u have problem vith nulling,try to null it with voltmetre in ac,put the rx working in circuit and probe also rx with voltmetre at mv ac,just try to get 4mv by moving rx in to tx,this is the simple nulling onlinr��

[waleed]

Hey waltr, check the video, I'm really surprised with the results, the LCR I bought I found that It needs to be calibrated, so after I calibrated it I measured the TX coil and it was 6.6mH, and then I made the RX coil it was 8.3mH (I know it's too high I'll adjust it later) and I didn't even constrain it yet, SO I just decided to attach it to the device and see how it would act (remember, RX coil still not constrained because I may remove some turns to get proper inductance) and then I turned the device on it gave a single beep as normal and it was so quiet, I just put the GB pot to the mid range and then moved a piece of ferrite and I overlapped the coils until the ferrite got rejected, after that I switched the disc switch to disc mod, so iron is rejected then I started to move the disc pot until foil is rejected (I just moved it a little bit not too much), the thing got me surprised with the result is that I'm pretty sure that RX inductance isn't correct and the coil is not constrained yet, I'll go to the uni tomorrow and make sure to get the 1.6kz difference between the two coils (by removing some turns from RX coil), I believe that the depth wasn't that good because the difference between TX and RX isn't 1.6kz and I also believe that the null wasn't perfect as well. I'll see tomorrow what will happen when I go to the uni and check everything.

https://youtu.be/cfXjZVju8Yw

[waltr]

Unknown how accurate the meter is but looks reasonable.
Most important is that the RX and TX coils are different by 0.5mH.
Since both coils are close I would trust that meter to show what the difference is.

Then use the method in TGSL 101.pdf using the TX oscillator and measure the frequency of each coil.

[waleed]

Waltr, can you check the image below and give me your opinion, I bought this LCR meter like about 25$,I just finished TX coil and I measured it with this lcr after I constrained the coil (the inductance was a little bit low before the constraining), I really don't know how accurate this device is.

https://i.ibb.co/w7xThyT/20200221-220144.jpg

[waltr]

"As you showed" is the correct one, "showed" in the past, "show" means now (present). And I believe he said "correct" for the whole Nandor post.

Yes.
Sorry for English ambiguity.
I agreed with Nandor's entire post.

[WM6]

"As you showed" is the correct one, "showed" in the past, "show" means now (present). And I believe he said "correct" for the whole Nandor post.

Thank you.

I found on Quora this explanation;

"Showed" is past tense and "shown" is past participle; similar, but not the same.

(use "showed" as this) past tense is a tense we use to express an action in the past.

(and use "shown" as this) past participle is a form of the verb, but not a tense, and it can't be used alone as verb.

Sorry again - to jump out of theme.

[waleed]

You mean: "... as you showed" ?

Sorry to disturb here, but as not native English speaker, I simply wish to know what is correct:

"as you showed" or "as you show" ? What is difference in meaning? I wish to improve my English.

"As you showed" is the correct one, "showed" in the past, "show" means now (present). And I believe he said "correct" for the whole Nandor post.

[WM6]

correct

You mean: "... as you showed" ?

Sorry to disturb here, but as not native English speaker, I simply wish to know what is correct:

"as you showed" or "as you show" ? What is difference in meaning? I wish to improve my English.

[waltr]

Hi

TL071 ot TL081 is a good replacement, I use booth maybe 071 is better because of low noise. NE5534 does not work here it gives continous sound.

4 pin connector is good as you showed.

correct.

[waleed]

Hi

TL071 ot TL081 is a good replacement, I use booth maybe 071 is better because of low noise. NE5534 does not work here it gives continous sound.

4 pin connector is good as you showed.

Much love Nandor thanks.

[Nandor]

Hi

TL071 ot TL081 is a good replacement, I use booth maybe 071 is better because of low noise. NE5534 does not work here it gives continous sound.

4 pin connector is good as you showed.

[waleed]

Waltr, the concentric coil doesn't seem to work properly so I decided to make the dd one, but I have some questions going on my mind make me not comfortable, first I did use the tl081 instead of lm308 it is ok or ne5534 would give better performance?, second I used 4 pins connector and soldered the cable wire shield to the TX end from both sides of the cable it is fine?

https://i.ibb.co/br5fq1N/1582242261519.jpg

[waltr]

I think I measured RX wrong, I should connect the RX to the TX oscillator alone and then check the frequency it should be almost 13.9khz right?

Correct.
But remember it is the difference that really counts.
So if TX oscillates at 14.9kHz, the RX Coil connected to the oscillator should be near (14.5-13.9kHz = 0.6kHz) 14.9 - 0.6 = 14.3kHz.

You can also TUNE the TX oscillator by adding C across the tank cap to bring the frequency down. I did do this on my TGSL. Try adding 1nF across C2 and measure TX coil frequency.
Add more until you get 14.5kHz.
Then the RX coil on this oscillator should run at 13.9kHz.

By using the same oscillator to check the coils you are actually check that the TX verse RX coils have the correct difference in inductance. This is the important value to obtain GB, disc and depth.

[waleed]

Ideally, the TX coil AND Oscillator should be 14.5kHz with the RX coil running at 13.9kHz on the TX's Oscillator circuit as in Dbower's TGSL 101.pdf.
What is actually important is the TX and RX coils have a difference of about 0.5mH. The actual TX Frequency can be different from the ideal 14.5kHz.

How did you measure these frequency? Are you sure you didn't mix them when posting?
The lower inductance would oscillate at a lower frequency if connected to same oscillator circuit.

I think I measured RX wrong, I should connect the RX to the TX oscillator alone and then check the frequency it should be almost 13.9khz right?