VLF Newbie

[porkluvr]

WHICH Whites patent are you talking about?

Oh, of course. THAT one.


edit 1: No, really. Which one??

edit 2: Patents are categorized with a number which makes it relatively easy to avoid CONFUSION or AMBIGUITY.

Would you be referring to US4293816, or some other?

[FreezonePK]

I am sorry, I meant I put a 100uF capacitor across the recieve coil. And Instead of 44uF I mean 0.44uF capacitors across the transmit and bucking coil.

I decided to redo the coils and more closely follow White's patent.
How does this sounds:
f0=8 KHz.
Tx:69 turns, 10" diameter, L=3.819mH
Bucking: 17.25 turns, 5" diameter L=0.125mH
Rx=207 turns, 5" diameter

0.1uF capacitors across RX and Bucking coil.

If you could response quickly that would be great on this new configuration. Does it sound alright? Is Tx turns correct?

[porkluvr]

Several things. Why would you place a 100uF across a tuned circuit? What does that do to the tuning??

Also, you would need approximately two 220nF (not 22uF) capacitors in parallel if you want to tune 8kHz with the TX coil you described.

If you need more help, how about you post a partial TX schematic?

[FreezonePK]

Hello Geo Community,

I am an young engineer in training in North America and decided to tackle my first metal detector. Me being nieve, I chose to use VLF detection. I have encountered a few roadblocks in building a coplanar coil. I am on my third attempt on nulling and tuning the coil and it seems to fail each time. Here is my lately configuration:


I make use of 22 AWG solid core wire. The transmit coil is 10” across, has 36 turns, and has an inductance of 0.782 mH (from coil calculator applet). The bucking coil is 5” across, wired around the receive coil, has 9 turns (36/4), and has an inductance of 0.029 mH. The receive coil is 5” across, and has 18 turns. There is no shielding for the transmit and recieve wires, and the tuning capacitor is placed on the breadboard which is located at the end of the recieve and transmission wires. (not on the coil assembly like in other examples seen). The operating frequency is 8KHz, and the tuning capacitor value is 44uF(x2 22uF caps). I place a capacitor across the transmit coil of 100uF to reduce noise.



Is this setup to 'ghetto'? Here is some pictures: Edit: I can't see the pictures in forum after I posted but here are the links. http://img36.imageshack.us/i/photo1so.jpg/ http://img15.imageshack.us/i/photolb.jpg/



If you look at oscilliscope I put in a 800mV pk pk, and get out 4.08 mV pk to pk. I noticed that if I remove my capacitors across the bucking and transmit coil it doesnt't change the output by much. Any suggestions?

Cheers,

Justin