Tesoro 5pin 8" Coil Inductance?

[lunarunderground]

I need a little help determining the inductance of an 8" concentric coil - 5 pin, originally came with the Bandido uMax. I'm trying to tune this in with the IGSL, but inductance is a new terrirtory for me and although I think I understand the basic concept and use of the formula, I'm coming up with numbers that don't quite seem to make sense. Any help at all would be great! Thanks! (Everyone was once a novice right?) ...

[kliner]

All the 5 pin coils are standard, around 6.0mh for the TX and around 6.5mh for the RX

[satdaveuk]

The tesro 8" coil with 5pin is as follows: 5.7mh-6.2mh resistance runs between 20-22 ohms.

Regards

[Dr Vel]

On this subject is there a capacitor inside the coil head? IIRC it was the RX coil but I am not near my notebook right now to see what I recorded. It is an 8 inch coil from a Pioneer 101 which I am using in my first attempt at building a modified Bandido II circuit (which I have also added some of my own mods to). The reason I ask is when sending pulses to the coils one at a time I see a short ring the other coil does not exhibit. As only one rings I assume it is not due to my test setup or scope connection (which appears to only add a very few picofarads, and this ring in in the audio range). When I have time I will build a dip meter for audio to ultrasonic frequencies I designed which will quickly allow me to determine actual resonant LC frequencies to allow easy tuning of TX/RX coil capacitor combination's. Was planning on building it as my next project but this ring in one coil makes me suspect Tesoro has at least one capacitor inside the head itself, which a dip meter would easily determine. Not wanting to tear into a perfectly good search head I am thinking I should stop on the MD and build the test instrument first, unless someone here has taken this model coil apart and knows the answer.

I should add the first post "I'm coming up with numbers that don't quite seem to make sense" makes me think there may be one capacitance value inside the sealed head assembly as it would answer his question as well as mine.

[Qiaozhi]

On this subject is there a capacitor inside the coil head? IIRC it was the RX coil but I am not near my notebook right now to see what I recorded. It is an 8 inch coil from a Pioneer 101 which I am using in my first attempt at building a modified Bandido II circuit (which I have also added some of my own mods to). The reason I ask is when sending pulses to the coils one at a time I see a short ring the other coil does not exhibit. As only one rings I assume it is not due to my test setup or scope connection (which appears to only add a very few picofarads, and this ring in in the audio range). When I have time I will build a dip meter for audio to ultrasonic frequencies I designed which will quickly allow me to determine actual resonant LC frequencies to allow easy tuning of TX/RX coil capacitor combination's. Was planning on building it as my next project but this ring in one coil makes me suspect Tesoro has at least one capacitor inside the head itself, which a dip meter would easily determine. Not wanting to tear into a perfectly good search head I am thinking I should stop on the MD and build the test instrument first, unless someone here has taken this model coil apart and knows the answer.

Tesoro search heads do not contain any capacitors, only coils.

[kliner]

I would be interested in building an audio frequency dipmeter as well, if anyone has a good schematic !

[Dr Vel]

Thanks for the quick answer. Do you think the small amplitude ring I see is merely a large amount of turn to turn capacitance in the larger coil combined with capacitive loading from the shield? Have to find my notebook to see where my timebase was set on the scope but the ring was much lower in frequency than the 50 microsecond pulse I was applying. This is my first foray into the electronics behind metal detectors so I am still uncertain of many factors.

[Qiaozhi]

Thanks for the quick answer. Do you think the small amplitude ring I see is merely a large amount of turn to turn capacitance in the larger coil combined with capacitive loading from the shield? Have to find my notebook to see where my timebase was set on the scope but the ring was much lower in frequency than the 50 microsecond pulse I was applying. This is my first foray into the electronics behind metal detectors so I am still uncertain of many factors.

Assuming you have calibrated your scope probes, then any ringing in the signal is most likely due to interwinding capacitance in the coil, combined with the capacitance of the cable.

The fact that Tesoro coils do not contain any tuning caps is why these are popular for DIY projects.

[satdaveuk]

As previously said the Tesro 8" brown coil has no CX installed so its classed as a untuned coil, when measuring on my coil tester without Cx, RX= 45.79KHZ TX= 44.69KHZ.

Hope thats of some help

Regards

[Dr Vel]

Thanks for the answers. Back to building my board.