Aquasound

[dbanner]

The Nautilus and Aquasound are essentially the same coil, TX and Rx front end.
I always thought that if Jerry's auto balance circuit from the dmc2bA is added to the aquasound, then you would have a great metal detector for the white sand beaches and seas. Problem here is that nobody has a schematic for the circuit.

Fiddling with those feedback pots in order to set up the detector is bound to turn off but the few hard core hunters.

[Melbeta]

Semtech used what I believe was a figure 8 coil, to decide if the target was positive or negative, all you had to do was see if the target was under the positive hole or the negative hole. Now I think dual TID meters for each hole would be superior for target guessing... Melbeta

[dbanner]

If an owner of a dmc2bA could be persuaded to take some pics of the daughter board contained in the chassis box, then the circuit schematic could be had.

Melbeta, nice to see you're still above ground. When people like yourself don't report in from time to time, well, you know what I mean.

[Altair]

I am trying to balance my center tapped concentric coplanar coil, it's not an easy task! playing a bit I get a minimum of about 88mV that is not ideal indeed. the difficult is also to mantain the same inductance of the two semi-coils due to different path of wires that occour during winding.
Any tips are welcome.

[dbanner]

Connect the feedback pots and adjust. You should be able to transition through either side of 0 volts on the RX V(out). Perfect null is impossible by mechanical geometry unless you put small tuning inductor in series. Only possible by electrical means.

Or you may wish to play around with small loops of wire for entire day. Remember there are two feedback windings, hence two fine tuning loops.

[dbanner]

Another idea would be to balance each half separately and then connect together, although I never tried it.

[Altair]

Connect the feedback pots and adjust. You should be able to transition through either side of 0 volts on the RX V(out). Perfect null is impossible by mechanical geometry unless you put small tuning inductor in series. Only possible by electrical means.

Or you may wish to play around with small loops of wire for entire day. Remember there are two feedback windings, hence two fine tuning loops.

Yes, I will see with pots if low nulling is really needed.

[dbanner]

Also, 6mv peak to peak was achieved in White's concentric coplanar type coil. In the patent for that coil is use of electrostatic shield ( a layer of foil) between the RX coil and the feedback coils to prevent capacitative coupling between Rx and feedback. This electrostatic shield is connected to the D.C ground.

Maybe this is required to be able to achieve a deep null.

[Altair]

Also, 6mv peak to peak was achieved in White's concentric coplanar type coil. In the patent for that coil is use of electrostatic shield ( a layer of foil) between the RX coil and the feedback coils to prevent capacitative coupling between Rx and feedback. This electrostatic shield is connected to the D.C ground.

Maybe this is required to be able to achieve a deep null.

Thank you dbanner!

You focused me on an important detail I was missing!

[dbanner]

Tomorrow I begin making the PCB. So we can make this project together and compare results. Will be good experience.
I will put pics of my finished PCB tommorow.

[kt315]

DB, i had told how to get deep null and how whites gets deep null. 0.00uV. you have to read again a thread.
https://www.geotech1.com/forums/show...er-coil-inside

[dbanner]

DB, i had told how to get deep null and how whites gets deep null. 0.00uV. you have to read again a thread.
https://www.geotech1.com/forums/show...er-coil-inside

Ah yes, I remember now, a closed loop. Thanks for that kt.

[Altair]

Concentric coplanar coil balancing seem to be not an easy task. The two bucking coils setting left me an high residual voltage (about 88 mV). Oscilloscope show me a distortion of RX signal that is not present without bucking coils and this is the cause of residual high voltage.

[dbanner]

A distortion of the RX signal might be caused by an imbalance of the two buck coils.
That is probably why the patent specifically staes to balance the RX for zero phase shift, the feedback pots will fine balance the voltage null.
I am only guessing what could be the problem.

Just wind the buck coils to be identical, so they impart equal effect on the rx. Use sufficient number of turns to bring the rx in the ballpark of null, but with zero phase. Let the feedback pot do the rest.

[dbanner]

Soon I hope to return to this project, in a few days time I will begin testing a new coil.