IB Rx coil at Tx off

[ZED]

Don't forget voltage ratings, that's why I use higher wattage parts even if overkill. Higher wattage resistors tend to also have higher voltage rating. Less heat less noise.

Agreed ! with 2 ma through it i thought it would be ok but when you factor in the voltage ,not so ok.

[green]

Ummm what about when the coil current gets dumped into the capacitor at the end of the TX period ? My sim shows 3 amps.

It's average watts over the whole Tx and Rx period. A perfect capacitor doesn't lose energy, just stores or transfers energy.

[green]

Made one of the 24in figure8 Rx coils. ID_24.5inches, 20turns AWG28 magnet wire. Measures 827uH, calculates 601uH using a flat spiral calculator. SRF 1MHz. Calculates 31p coil capacitance. Anyone have an idea why measured inductance would be 37% higher than calculated.
Measured inductance calculated from resonance(17500 Hz)with a 100n polypropylene capacitor across the coil. 100n capacitor measures 100n with two capacitance meters I have.

[green]

Working on second Rx coil for 24in fig8. Wondered if I could chart a target decay with the 30in DD coil. Looks good out to 90us. Should be able to compare 30in DD with 24in figure8 for signal strength. If things look good, time to make Tx circuit with integrator to compare detection distance. Can bottom spaced 2.25 inches from coil.

[green]

Finished winding the second Rx coil(SRF=980kHz, 818uH, 8.87R) and Tx coil(SRF=770kHz, 717uH, 1.34R).

[green]

Working on second Rx coil for 24in fig8. Wondered if I could chart a target decay with the 30in DD coil. Looks good out to 90us. Should be able to compare 30in DD with 24in figure8 for signal strength. If things look good, time to make Tx circuit with integrator to compare detection distance. Can bottom spaced 2.25 inches from coil.

Charted Coke [email protected] with the fig8 coil. Neither coil shielded, hope they clean up some shielded. Was a little surprised how close the amplitudes were. Be interesting to see how close they are at greater distances.

[dbanner]

Made one of the 24in figure8 Rx coils. ID_24.5inches, 20turns AWG28 magnet wire. Measures 827uH, calculates 601uH using a flat spiral calculator. SRF 1MHz. Calculates 31p coil capacitance. Anyone have an idea why measured inductance would be 37% higher than calculated.
Measured inductance calculated from resonance(17500 Hz)with a 100n polypropylene capacitor across the coil. 100n capacitor measures 100n with two capacitance meters I have.

Green, curious is the great disparity between the measured inductance and the Inductance based on the flat spiral calculator. You have stumbled on to something I noticed while reading a document on the topic of Inductance, srf and self capacitance.
I always thought that distributed capacitance ( derived from the interwire capacitance played a dominant role in the self capacitance of inductors, of which the flat spiral coil is part of. I was surprised to learn that this is not the case at all for bare wire( coated enamel)
What's more, the coil self capacitance changes when it is connected to any circuit, which I found astonishing (and no, I'm not referring to the capacitative loading of the circuit)

Anyways, 37% difference is very big in my opinion, and it would bother the living daylights out of me, until I figured out why. Either the coil calculator is rubbish or some other phenomenon is occurring.

[dbanner]

Which brings me to the issue of Q factor and ohmic losses vs. frequency dependent inductance measurements. The first two parameters, inductance and Q, are very dependant on the testing frequency and the instrument used for testing. Maybe not relevant in this case, but certainly something worth noting.

[green]

Green, curious is the great disparity between the measured inductance and the Inductance based on the flat spiral calculator. You have stumbled on to something I noticed while reading a document on the topic of Inductance, srf and self capacitance.
I always thought that distributed capacitance ( derived from the interwire capacitance played a dominant role in the self capacitance of inductors, of which the flat spiral coil is part of. I was surprised to learn that this is not the case at all for bare wire( coated enamel)
What's more, the coil self capacitance changes when it is connected to any circuit, which I found astonishing (and no, I'm not referring to the capacitative loading of the circuit)

Anyways, 37% difference is very big in my opinion, and it would bother the living daylights out of me, until I figured out why. Either the coil calculator is rubbish or some other phenomenon is occurring.

I wonder why the big difference. I calculate inductance with resonance with a 100n capacitor across the coil excited with an operating PI. Have compared calculated inductance with a 10n and 100n capacitor across the coil, usually less than 1% difference. Thinking my measurement method is correct. Some possibility's, measurement method, coil calculator, my winding isn't clean enough. Any other possibility's? All the coils I've made for this project calculate 30 to 40% lower than what I get. Based the calculation on a round coil with the same circumference. Would expect the non round coils to measure lower than if they were round.

[Qiaozhi]

I wonder why the big difference. I calculate inductance with resonance with a 100n capacitor across the coil excited with an operating PI. Have compared calculated inductance with a 10n and 100n capacitor across the coil, usually less than 1% difference. Thinking my measurement method is correct. Some possibility's, measurement method, coil calculator, my winding isn't clean enough. Any other possibility's? All the coils I've made for this project calculate 30 to 40% lower than what I get. Based the calculation on a round coil with the same circumference. Would expect the non round coils to measure lower than if they were round.

Which spiral calculator are you using?

[green]

Which spiral calculator are you using?

http://www.deepfriedneon.com/tesla_f_calcspiral.html

Some 8inch round, measured 10% higher than calculated. Looks like the difference measurement using 10n and 100n was over 1%, less than 2%.

https://crystalradio.net/professorcoyle/index.shtml

[Carl-NC]

Green, curious is the great disparity between the measured inductance and the Inductance based on the flat spiral calculator. You have stumbled on to something I noticed while reading a document on the topic of Inductance, srf and self capacitance.
I always thought that distributed capacitance ( derived from the interwire capacitance played a dominant role in the self capacitance of inductors, of which the flat spiral coil is part of. I was surprised to learn that this is not the case at all for bare wire( coated enamel)
What's more, the coil self capacitance changes when it is connected to any circuit, which I found astonishing (and no, I'm not referring to the capacitative loading of the circuit)

What's the document? Self-capacitance should not depend on the circuit it's connected to.

[dbanner]

Discovered a super easy way of calculating the Q factor. When measuring the srf on oscilloscope ( either by pulse excitation or by driving a square wave), just count the number of cycles in the ring down from the start to when the ring down decays to half of it's peak amplitude and multiply the result by 5 and that is the Q factor of your pi coil.
Here is the video, where a spider coil is used in the demonstration.
https://m.youtube.com/watch?v=tjbK4LsOQRk&t=629s

[dbanner]

What's the document? Self-capacitance should not depend on the circuit it's connected to.

Here is the document. Perhaps I am not understanding, but this connected wires as part of the coil and not part of the circuit stood out to me.

[dbanner]

The difference is subtle in that a coil on its own has its own self capacitance which can only be measured when the coil is connected, in which case the connecting wires are now considered part of the coil and not part of (belonging to) the measuring circuit thus implying that the self capacitance has been altered by the connecting wires.
Hence it is only practicable to measure srf and self capacitance of our pi coils when it is connected to the cable we intend to use as part of the final detector hardware.
That's my take away from it.
But I agree that the intrinsic self capacitance of a coil is independent of the circuit.