Friends from Russia

[Esteban]

Think first version is the application notes by Signetics. There are many different -some elaborate- projects: French, Italian, Brazilian... The Brazilian -interesting- is the last I collect based on 565.

Another PLL -but with base on 4046- was published by Elektor: only one turn coil-coaxial cable...

[Geo]

Yes please.
If my version is different I will post that as well.

Detection of a table watch at 40cm (15.75") is really good for such a simple circuit. It appears that your tests were more successful than mine. I actually found that the sensitivity was poor, and matched the University paper's results very closely.

I look forward to seeing the design that you used.

Hi Qiaozhi. Today i found the magazine with the schematic. The schematic is the same with attached file. Q2 Q3 Q4 and Q5 are 2N4403. I believe that with a big coil it will detect at large distance and has the ability to discriminate ferrous and no ferous objects. If i remember good it was a litle unstable.

http://thunting.com/geotech/forums/a...0&d=1144370375

Regards

[Geo]

Think first version is the application notes by Signetics.
Another PLL -but with base on 4046- was published by Elektor: only one turn coil-coaxial cable...

Hi Esteban. Did you try it?

[ivconic]

A hint...


Hi !

Not big deal if skip conventional way of making coil and use Cu pipe, rolled in a circle, with slice opened flange, for 1-2mm and also used that "holder"as gnd as well as F.cage....maybe help !? BFO has lack of stabillity anyway...
regards

[Esteban]

Geo, only is for big items this one turn coil MD, no very enthusiast I'm constructing it...

[Geo]

Geo, only is for big items this one turn coil MD, no very enthusiast I'm constructing it...

Hi Esteban.
I thought that perhaps it was a good solution for big objects with a coil 70.. 80 cm.
Yes I believe the same with Ivcomic about bfo stability.
Regards

[Esteban]

Hi, yes is true, you can build a big search coaxial coil. In this case hope the shield of the coaxial is enough for to mantain the stability.

[Geo]

Hi, yes is true, you can build a big search coaxial coil. In this case hope the shield of the coaxial is enough for to mantain the stability.

The major reason of the bfo bad stability is the frequency shift so the bad quality of capacitors is the major reason (the coil is major of change only if has very thin wire and it heats)

[Qiaozhi]

Geo, only is for big items this one turn coil MD, no very enthusiast I'm constructing it...

Hi Estaban,

This looks like a design from Elektor. Correct?

[Esteban]

Yes, you're right.

[6666]

Qiaozhi

or anybody
do you have a copy of the third circuit ?
thanks
6666

[Qiaozhi]

Qiaozhi

or anybody
do you have a copy of the third circuit ?
thanks
6666

The third circuit is attached to post #14.