Need help to build tesoro coil

[gregory59]

Hello,

I'm going to build a concentric coil for tesoro bandido ii but somebody can explain to me how to cancel the receive field ? is it necessary to have an oscilloscope ???

Thanks

[Qiaozhi]

Coil Nulling

Hello,

I'm going to build a concentric coil for tesoro bandido ii but somebody can explain to me how to cancel the receive field ? is it necessary to have an oscilloscope ???

Thanks

Personally I use an oscilloscope, it's just easier. Anyway, you're making your life difficult by not having one. They are fairly inexpensive to buy on eBay, and you don't need anything fancy. I use a Gould dual-beam 20MHz OS300, but I also have a Scopex 4D 10, and even that is perfectly adequate for this type of work. Try and get a dual-beam scope if possible.

[Largesarge]

I got a BK 2125 dual trace 20MHZ off ebay for real cheap. The description said that trace 2 was missing, put I decided to take a chance.


When I got it I plugged it in and started checking things out and sure nuff trace 2 was missing. Just for the heck of it I twisted the POS knob and low and be hold the trace came scooting down the top.

The guy admitted that he didn't know anything about O'scopes and this just proved that. So now I have nice little scope for less than $50, shipping and all.

[gregory59]

How use oscilloscope to cancel RX field ???

Hello,

I don't have oscilloscope but i use my soundcard with software to emulate an oscilloscope ( it's working very well => i can see the Tx and Rx signals ). But now somebody can explain to me what i must see on the oscilloscope when the the Rx field is cancelled ???
Somebody can show a picture ???

Thank you.
gregory59.

[Qiaozhi]

Cancelling the RX signal

Hello,

I don't have oscilloscope but i use my soundcard with software to emulate an oscilloscope ( it's working very well => i can see the Tx and Rx signals ). But now somebody can explain to me what i must see on the oscilloscope when the the Rx field is cancelled ???
Somebody can show a picture ???

Thank you.
gregory59.

It's very simple. Connect the TX signal to channel 2 and set the external trigger to channel 2. Then connect the RX coil (with suitable tuning capacitor) to Channel 1, and adjust the number of turns on the nulling coil and the relative coil positions to achieve the smallest possible amplitude for the RX signal. When you are happy with the result, glue the coils into place. If you leave a small loop unglued it is then possible to make some final adjustments once the glue has set. Any residual RX signal can be cancelled electronically.

[gregory59]

thank you Qiaozhi,

But what does it mean :

- the external trigger ???
and
- with a suitable capacitor ???

can you make a schema

Thank you
Gregory59

[Qiaozhi]

Scope Training

thank you Qiaozhi,

But what does it mean :

- the external trigger ???
and
- with a suitable capacitor ???

can you make a schema

Thank you
Gregory59

Hi Gregory59,

All oscilloscopes have a knob that you can adjust to set the trigger level and hence stabilize the trace on the screen. You probably have a "software knob" on your PC / sound card combination that does the same thing. On a dual-beam scope you can also select which of the two channels is used to provide this trigger. In my example I suggested connecting Channel 2 to the TX output and triggering the display on this signal. Now you can connect the RX signal to Channel 1. The TX output needs to be used as the trigger because it is the stable reference, since you are trying to measure the RX output for the purposes of finding the null point.
The capacitor I mentioned needs to placed in parallel with the RX coil so that it is tuned close to the TX frequency. You can easily calculate the required value using this formula -> C = 1/(w^2 * L)
where w = 2*pi*F
F = TX frequency in hertz
L = RX coil inductance

Hope this helps!