Rookie asks a question.

[sanmao998]

I tested the metal detector and found a good depth. Wanted to use his mainframe to make a large concentric coil. It's about 24 inches. TX24 inch, RX size is more or less suitable. In addition, how much inductance is appropriate? I am a novice. If you need to measure the parameters of the original coil, please tell me what you need to measure, and I will measure it and publish it. Thank you very much. I don't speak English. Translation software is required. So the question of expression can be vague.
The picture below shows the original coil taken apart

[Artyom]

First, tell me, what are you planning to look for? A 24-inch coil is a lot, and why a concentric coil? And in order to make a new coil, you need to measure the inductance of the transmitting and receiving coils.

[sanmao998]

只是为了提高对大型物体的检测深度。而且这块主板有鉴别功能。现在我需要测量原始线圈的电感吗？然后做一个 大线圈，和原来的线圈一样的电感可以吗？

[Qiaozhi]

只是为了提高对大型物体的检测深度。而且这块主板有鉴别功能。现在我需要测量原始线圈的电感吗？然后做一个 大线圈，和原来的线圈一样的电感可以吗？

Please make your posts in English.

[kt315]

1. you have to measure L of Tx and Rx coils.
2. to calculate number of turns in both. Nt
3. to calculate Kt, transformation, be cause VLF coil is simple transformer with 'poor link between the coils'. Kt=Ntrx/Nttx
4. to do new size Tx coil with SAME L. add 2-5% on a lost.
5. to re-calculate Rx coil turns using Kt. Ntrx=Kt x Nttx
6. you have to set me LIKE now. look at right low edge of post. better if you set me LIKE more times.

樂趣

[ivconic]

Please make your posts in English.

From this moment the new reign of terror comes into force and takes over the forum!
From now on, please post everything in Serbian!
Or you will suffer terrible and unfathomable consequences!
85% of Chinese are already learning Serbian without hesitation! Smart people!
...
Because Serbian is the language of the future!
Global futures!
And no jokes on that topic will be tolerated!
George, from this moment on, your name is Đorđe!
An old Serbian name!
Be proud of it!

[ivconic]

https://urbancube-rs.translate.goog/...x_tr_hist=true

[kt315]

7. set up LIKE! to ivconic too.

[sanmao998]

I am very sorry that I do not speak English and use the translation software to carry on the conversation. I just want to make a bigger coil. Can improve the detection depth of large objects. I don't know how to proceed.

[pito]

That is easy.
From picture it is look like Tx coil is a part of oscillator, to check that put some ferrite on the coil you should have frequency decreasing or amplitude. Next you need to recreate circuit of the oscillator from PCB or find factory shematick, what is the name of metal detector ?

[Carl-NC]

sanmao998, building a concentric coil is conceptually simple, but in practice it is not a beginner project. Read this article for how to build one:

https://www.geotech1.com/pages/metde...planar_300.pdf

You need to reasonably match the TX inductance and resistance, maybe 5-10%. Usually the RX inductance and resistance are not as critical, maybe 20%. Making a stable enclosure and shielding it will be the hardest part.

[pito]

sanmao998,

You need to reasonably match the TX inductance and resistance, maybe 5-10%. Usually the RX inductance and resistance are not as critical, maybe 20%. Making a stable enclosure and shielding it will be the hardest part.

This is not necessary, in most cases you need to adjust the Tx frequency, i.e. the LC circuit, you wind the coil 100 turns (0.4 mm wire or similar) ignoring the inductance value, just adjust circuit by changing the C value.
Rx 100 turns 0.2 wire.
Bucking coil 30 turns 0.4 wire - add or subtract number of turns = adjust for minimum voltage on Rx coil

[Carl-NC]

Yes, if you know what you're doing. If you don't, then replicating the existing inductances is far easier.

[sanmao998]

That is easy.
From picture it is look like Tx coil is a part of oscillator, to check that put some ferrite on the coil you should have frequency decreasing or amplitude. Next you need to recreate circuit of the oscillator from PCB or find factory shematick, what is the name of metal detector ?

This is a very old metal detector sold in China, mainly used by homeless people or to buy scrap metal. But it works great.

[sanmao998]

sanmao998, building a concentric coil is conceptually simple, but in practice it is not a beginner project. Read this article for how to build one:

https://www.geotech1.com/pages/metde...planar_300.pdf

You need to reasonably match the TX inductance and resistance, maybe 5-10%. Usually the RX inductance and resistance are not as critical, maybe 20%. Making a stable enclosure and shielding it will be the hardest part.

Thank you very much, Carl. I have no professional knowledge. Can only try to explore the production.