Clone Chance Help

[6666]

Tried calculating interwire capacitance of above coils. Got a small difference, wondering what I might be doing wrong. I've read winding spiral coil results in low capacitance but shielding adds a lot of capacitance. Other than some tests I've done these are the only ones that list values that I can remember. Does anyone know where a spiral coil listed values that suggested a low SRF or high capacitance? Including picture of the last coil test I did comparing flat vs basket coil. Low capacitance and shielding added very little.

Hi Green with your basket coil by any chance did you happen to measure the SRF while still on the former with all the straws etc

[green]

Hi Green with your basket coil by any chance did you happen to measure the SRF while still on the former with all the straws etc

Probably did measure it on the form with tooth picks. Think it was the same as after removing from form. Have a 12inch flat basket, AWG28 magnet wire still on the form. Measures 361uH, SRF=2.4MHz on the form.

[green]

I think the general consensus is flat spiral coil gives lowest possible interwire capacitance, I would be interested in the relationship between early sampling and self capacitance and damping resistor, assuming that you have a fast switch off tx driver circuit.

Zapped my mono coil circuit awhile back. Been using separate Tx Rx coils with a differential amplifier. Put a mono amplifier together to get a scope picture of the 200mm flat radial. Probably close to good as I can get with this coil.

[dbanner]

Mr. Green, your work is very good. The flat basket mono has the lowest self capacitance, you are testing the FLAT RADIAL?
From what I see, the coil voltage dissipate after 5uS(with no target). Am I reading it correctly? This would imply a pretty fast coil?

[dbanner]

Could you describe the TX driver circuit?( not necessary to put schematic)

[green]

Could you describe the TX driver circuit?( not necessary to put schematic)

I tested the flat radial. Shouldn't be any difference. Either coil has less capacitance than 1 feet of lead wire. The circuit resonance(input resistor not connected, no Rd) was 1MHz, lot less than coil resonance.

The amplifier is two stage. X15 and X20 for a gain of 300. Coil connected to -input of first amplifier with 1k resistor. Adjustable Rd across coil to adjust best response. LT6237 op amp

[green]

I tested the flat radial. Shouldn't be any difference. Either coil has less capacitance than 1 feet of lead wire. The circuit resonance(input resistor not connected, no Rd) was 1MHz, lot less than coil resonance.

The amplifier is two stage. X15 and X20 for a gain of 300. Coil connected to -input of first amplifier with 1k resistor. Adjustable Rd across coil to adjust best response. LT6237 op amp

Tested both to see if there is a difference. Don't act the same, both overshoot as if underdamped. Overshoot decay longer than should be if underdamped. 1x1inch piece of aluminum foil(TC about 1.8usec)cancels overshoot. Probably not needed since looking for change in integrator out. Flat radial needed Rd added and adjusted to minimize overshoot. Both ended up about the same. The circuit in spice doesn't overshoot unless underdamped and with a faster overshoot decay. Don't know why the overshoot, any suggestions?