minimum sample delay

[green]

Carl's method of measuring resonance is most accurate, as the result will have included ALL of the capacitance (intended and unintended) of the TX circuit (i.e. coil, MOSFET, cable, internal wiring/routing, etc.). Also the correct damp resistance is not just a function of resonant frequency, but more importantly a function of the ratio of inductive reactance relative to capacitive reactance (which corresponds to the ratio of L to C as well as frequency). In other words if 2 coils have the same resonant frequency but different ratios of L to C, they require different damp R values.

Agree. Rd=pi*L*resonant frequency(circuit not coil resonance). My point was, it can matter where the measurement probe is connected. I wanted to record coil decay so I measured resonance with the probe across the coil. With the probe removed Rd increases from 1345 to 1530 ohms. Maybe the best place for the probe to measure resonance is amplifier out?

[KingJL]

"... Carl mentioned in another thread to disconnect Rd with an operating PI to check resonance..."

Carl's method of measuring resonance is most accurate, as the result will have included ALL of the capacitance (intended and unintended) of the TX circuit (i.e. coil, MOSFET, cable, internal wiring/routing, etc.). Also the correct damp resistance is not just a function of resonant frequency, but more importantly a function of the ratio of inductive reactance relative to capacitive reactance (which corresponds to the ratio of L to C as well as frequency). In other words if 2 coils have the same resonant frequency but different ratios of L to C, they require different damp R values.

[green]

Tried adjusting Rd, has a small effect on minimum delay time. I've been holding test coil near an operating PI to determine test coil resonance. Carl mentioned in another thread to disconnect Rd with an operating PI to check resonance. Think my way gives maximum resonance but Carl's way is better if trying to calculate Rd with formula Rd=pi*L*resonant frequency. Wanted to chart coil decay volts with coil critical damped. Coil resonance with leads 1.38MHz, in circuit with Rd disconnected and x10 probe across coil 1.03MHz, in circuit with Rd disconnected and probe near coil not connected 1.17MHz. Coil inductance=416uH. Rd=1.38*pi*416=1803 ohms, Rd=1.03*pi*416=1346 ohms, Rd=1.17*pi*416=1529 ohms. Recorded data with x10 probe across coil with Rd=1332 ohms. The decay TC(1.8usec) is less than calculated L/R(3.12usec). Should it be or am I doing something wrong? Anything else doesn't make sense with the scope pics or chart? Running out of things to try with existing circuit to lower delay. Maybe winding another coil. Any suggestions for the coil or other things to try?

[green]

Use real litz wire for all coils?

Was wondering the same, the reason for flat cable thread as an option for litz. A mono coil sees the coil wire as a target. Wondering if the figure eight Rx coil doesn't cancel. Can position a US nickel near one coil until amplifier saturates. Then adjust position of another US nickel near the other coil until amplifier out looks the same as no nickels. If it cancels nickels why wouldn't it cancel the coil wire? Maybe litz would be better but I think something else has a larger effect on reducing the delay with the figure eight coil.

[kt315]

What is required to get the no target signal near zero volts at 1 or 2usec?
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i think physics rule is one either coil for vlf or pi - the transformator has to have equal number of turns.

TX = RX. ie in IDEAL transformer with coefficient of transformation egual 1. thats is your 'near zero'.
another way you always get dizbalance.

[rickb]

Use real litz wire for all coils?

[green]

http://www.geotech1.com/forums/attac...4&d=1527807206 attachment from another thread.

Rx(two 1.5inch round coils connected figure eight) Tx(oval surrounding Rx). What is required to reduce sample delay to 2usec maybe 1usec? What measurements from existing circuit are needed if any? Maybe forget about existing circuit and define what is required to have sample delay at 1 or 2usec.

What is required to get the no target signal near zero volts at 1 or 2usec?