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Originally posted by Nandor
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correct.
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correct. -
You mean: "... as you showed" ?Originally posted by waltr View Post
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.Comment
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"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.Originally posted by WM6 View PostComment
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Originally posted by waleed View 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.Comment
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Originally posted by waleed View Post
Yes.
Sorry for English ambiguity.
I agreed with Nandor's entire post.Comment
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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.jpgComment
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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.Comment
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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/cfXjZVju8YwComment
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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��Originally posted by waleed View PostComment
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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..Comment
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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 
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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!
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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.Comment
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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.jpgComment
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As Waltr said, you should not seek to get the lowest null. The important thing is to get the phase offset correct.Originally posted by waleed View PostComment
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