Treasure Mate Pinpointer

[Altra]

Here is the schematic for the Treasure Mate pinpointer. These were built by Tesoro for another company. Unlike most pin pointers it is induction balanced. It also has a ground balance control. The sensor coil was built like the old Sunray probes. The tip has the RX winding and a short distance back is the TX winding. The core is a machined pvc rod. The probe is nulled by winding 7 or 8 counter turns from the RX coil over the TX coil. This induces an equal but opposite Tx field in the RX coil reducing the inductive coupling. In addition and the most interesting part of the circuit is the electronic nulling. It feeds some of the tx signal back to the rx allowing adjustment of the null for the X and R phases. The null circuit could be adapted to most vlf detectors.

These units are rare to find and I don't believe that many were sold? I decided to destroy mine for the cause. You can still find some old forum post by users around. The best info I could find was here

https://www.detectorprospector.com/t...omment-4172

[Carl-NC]

I remember these, never owned one tho. I didn't know it was an IB design. At White's I did an IB pinpointer (TRX) with the same coil design but did the fine nulling with a piece of ferrite tape. I find the fine nulling on this design to be interesting, it's electronic with both X & R null. In another thread we were just talking about e-nulled loops, this is one way to do it.

[dbanner]

Thanks Altra. Nice.
0.25mm or 0.3mm enamel wire? Both Tx and Rx same diam. wire, right? And what's the approximate diameter of the PVC rod? I assume there isn't any ferrite core inside the Tx coil. right?

[dbanner]

What are these?

[dbanner]

Test points?

[Altra]

Test points?

Yes, smd test points

[Altra]

Thanks Altra. Nice.
0.25mm or 0.3mm enamel wire? Both Tx and Rx same diam. wire, right? And what's the approximate diameter of the PVC rod? I assume there isn't any ferrite core inside the Tx coil. right?

The wire gauge is probably AWG #34. Because when I tried to duplicate it on the same core using AWG #32, the windings came out thicker. The core is plastic with no ferrite. I misplaced my notes on the windings and core. I believe it the outer diameter is 0.375in or 3/8th with 0.0625 groves for the windings. I am away till mid January and cannot measure the core or count the windings until then. I Recall about 43 turns for each winding. You can wind a test on some wood rod or plastic. Nothing is very critical only the counter turns (6-7) on the tx coil and position.

[dbanner]

Right, thanks.

[Carl-NC]

The coil I did for the TRX had a ferrite core for the TX coil only, like this:


You can also wind both on an air core but I found the ferrite improved depth a bit. If you also wind the RX coil on the ferrite then you end up with a magnetometer.

[ivconic]

15 cm in diameter.
Inductances and resistances are ideally matched.
I'm not sure which Tesora model these coils came with.

[Altra]

The coil I did for the TRX had a ferrite core for the TX coil only, like this:


You can also wind both on an air core but I found the ferrite improved depth a bit. If you also wind the RX coil on the ferrite then you end up with a magnetometer.

That is a nice drawing to illustrate the construction. If you draw a horizontal hourglass over the center of tx winding that will be the magnetic field form. So you want to bunch your counter turns to the frontend of the tx winding. You get a phase reversal on either side of the center. When I was making probes for Sunray we tried a ferrite core for a small run and found that ferrite expanded and contracted with temperature changes causing the probes to go out of balance in cooler temperatures.

[Altra]

15 cm in diameter.
Inductances and resistances are ideally matched.
I'm not sure which Tesora model these coils came with.

I believe the coils are matched. When you wind the 6 reverse turns of Rx over the Tx it reduces the inductance of the Rx

[Carl-NC]

When I was making probes for Sunray we tried a ferrite core for a small run and found that ferrite expanded and contracted with temperature changes causing the probes to go out of balance in cooler temperatures.

The TRX coil has an additional part not shown; there is a plastic bobbin that the coils are wound on, then the ferrite is slid inside the bobbin. So the coils are spaced off the ferrite. I don't recall any significant temp shift.

[Altra]

Using a bobbin would allow for expansion of the ferrite and not affect the windings. I was using factory made inductors to save time winding the coils and a smaller size over air core. It seemed like a good idea at that time.

[ivconic]

I know from radio engineering that the wire is NEVER wound directly on the ferrite, but paper, plastic, in rare cases mica and in even rarer cases capton is used.
I'm talking about "radio" times... today I see that with various "switch" transformers the wire is wound directly on the torus cores and rods.
...
I have another "hint" for those who would like to deal with this type of coils.
The longer the ferrite core is, the more focused the direction of movement of the magnetic field is.
Short core = wider the angle of the direction of movement.