Bandido Coil Resonances

[Mike]

My first post Here goes...

Looking at the Tesoro Bandido uMax schematic, and calculating the resonant frequencies of the Tx and Rx coils based on the coil data (on the Geotech web site), the Tx comes out at around 10kHz (per Tesoro spec.), but the Rx seems to be around 11kHz. This is the case for 5 of the coils listed - i.e. this is an intentional design decision by Tesoro.

Is this significant? Why would the Rx coil be detuned by 10%?

Thanks in advance for any replies.

[Sean Goddard]

As tesoro do not use capacitors in their coils, they actually have NOT resonant frequency, hence the fact that the same coils are used acros most of their range.

The FTx is selected by the caps in the TX Colpitts oscillator, and the Rx input cap is to provide a phase shift to aid in the balance of the coil when used with that specific machine. This is one of the reasons that tesoro coils must be "retuned" when they are swapped to a different machine.

[Mike]

Enlightened

the Rx input cap is to provide a phase shift to aid in the balance of the coil

I think that answers my question. I assumed - incorrectly - the Rx cap (C15 in the Bandido schematic) was there for frequency tuning purposes. But it's more for phase tuning purposes.

Thanks for your reply.

Mike

[ma330]

Re: coils bandido umax 2

please send for me coils schematic bandido ii u max .this is my mail :[email protected]
tank you

[Qiaozhi]

Bandido II uMax

please send for me coils schematic bandido ii u max .this is my mail :[email protected]
tank you

Schematic attached, as requested.
I believe that the TX coil is 5.9mH and the RX coil is 6.5mH.

[Unregistered]

My first post Here goes...

Looking at the Tesoro Bandido uMax schematic, and calculating the resonant frequencies of the Tx and Rx coils based on the coil data (on the Geotech web site), the Tx comes out at around 10kHz (per Tesoro spec.), but the Rx seems to be around 11kHz. This is the case for 5 of the coils listed - i.e. this is an intentional design decision by Tesoro.

Is this significant? Why would the Rx coil be detuned by 10%?

Thanks in advance for any replies.

On the Bandido schematic I see bellow, posted by Qiaoshy there is 33nF capacitor on the input. That one will certainly tunne the receive to the transmit coil to some degree.
There is one problem in this way. The cable , connecting the coil to the circuit, becomes part of what ever resonance tunning can occure in which case the cable is also part of the receive circuitry. That could lead to external interfearance problems.

[ma330]

hi :
i building circuit bandidoIIUMAX.BUT i have not coils this circuit .please give to me coils this circuit.turn and much and number and way build and diagram coils.ok?
wait for you .tank you. good BY.

[kt315]

read here of George Payne. useful.
http://www.jb-ms.com/Baron/gb.htm



Here are some general design parameters for a coil: Transmit Coil -- 25 to 30 turns of 22 gauge wire. Diameter 7 to 8 inches.
Receive Coil -- 200 to 300 turns of 31 gauge wire. Diameter 3 to 4 inches
Feedback Coil -- 6 to 10 turns of 22 gauge wire. Diameter same as receive.
Tank Capacitor -- 0.47uF

[ma330]

gold scan

hi ; tank you for coils bandido that send for me .
i have other question:
what is gold scan? how mach depth detecting metal?
please send for me pcb this circuit.
tank you.goodby

[Qiaozhi]

Coil Details

hi :
i building circuit bandidoIIUMAX.BUT i have not coils this circuit .please give to me coils this circuit.turn and much and number and way build and diagram coils.ok?
wait for you .tank you. good BY.

As you may be aware, the Tesoro coils are almost impossible to take apart, and we will need make an educated guess of the number of turns on the TX and RX coils.

I have measured the inductance values of a Tesoro coil and found them to be:
TX = 5.9mH
RX = 6.5mH (This includes the nulling coil which is in series with the RX coil.)

If we assume the inner radius of the TX coil is 7" (178mm) then we need 78 turns of 0.56mm (24swg) enamelled copper wire to achieve an inductance of 5.81mH.

Likewise, for an RX coil of 5" (127mm) we need 103 turns (6.5mH).
Possibly the RX coil is smaller than this at 4" (102mm) - it's difficult to know exactly - and in this case we have 119 turns (6.51mH).

The difficulty with constructing a copy of the Tesoro coil is knowing how many turns are needed for the nulling coil, as this contributes to the overall inductance of the RX coil. My advice would be to either buy a Tesoro coil secondhand and use that, or get as close as you can to 6.5mH for the RX coil and adjust the value of the capacitor appropriately to retune the circuit.

Anyway - good luck!

Maybe somebody (possibly Sean Goddard?) has dissassembled a Tesoro coil. If so, please can you post the details?

[ma330]

hi.
tank you for bandido colis taht send for me.
if this coil give ask to me i send schematic their for you........
tank you .very very much. good by