comparison

[Max]

I did think in this clue too... one man opened a coil... the all coil has a micro with integrated TX generator and ADC. it is clear... on TX coil is sinusoidal signal 20V AC, on RX coil is also sinusoidal following in the micro. from the chip a signal comes out already as kinda digital, discrete. I changed my opinion...

Hi,
yes... I think the micro there is for special purposes...

One of teh hardest problems with MD coils for VLFs is resonant designs need to compensate for drift.

What if the micro corrects that behaviour and let the coil operate in resonance or near-resonance mode ?

Just a guess... I don't know...

Think about... the micro has internal ADC and maybe that is good if you wanna e.g. measure peak rx voltage (at resonance you have max coupling and maximum of oscillations amplitude).
Then think about the possible existance of some kind of negative feedback signal who can be generated by micro to regulate some TX param, shift its frequency a bit more or less and so hit , exactly the RX section resonant frequency.
That way you can forget about analog compensation network and the like... and have a system always at top of performance.

Maybe the fact there's a micro+adc there is to achieve same results of a critically resonant tuned coil (like some expensive thing, nexus) and got these coils from standard production process... not critical handmade tuning.

If so, the advantage is obvious, you get great depth, but don't need days to make a single coil...

Am I right , maybe !?

Kind regards,
Max