Waveforms + Measurements

[moodz]

adding a sheild has no effect as the balanced flyback +/- 500 volts cancels out and there is no ground effect as there is no capacitive coupling to ground.

The ultra short pulse is a result of the ruthruff configuration ... delayed signal and undelayed signal is fed to diff amp ... see CL Ruthruff description of balun. The presence of target in "core" changes permeability which changes delay.

moodz

[Aziz]

adding a sheild has no effect as the balanced flyback +/- 500 volts cancels out and there is no ground effect as there is no capacitive coupling to ground.

The ultra short pulse is a result of the ruthruff configuration ... delayed signal and undelayed signal is fed to diff amp ... see CL Ruthruff description of balun. The presence of target in "core" changes permeability which changes delay.

moodz

But the ground should have a significant effect. The high mineral ground can change the inductance of the coil and hence the delay time. Of course, it's impedance too.

Aziz

[moodz]

But the ground should have a significant effect. The high mineral ground can change the inductance of the coil and hence the delay time. Of course, it's impedance too.

Aziz

True ... I will have to do more tests ... on real ground. I have 3 Kg of pure iron oxide and it shows no effect at all, also ferrites etc no effect. Only conductive targets show a response.

regards,

moodz

[moodz]

A quick test of Induction Balance.

Very crude but here are the results of using induction balance using two differential coils.

It was very easy to position the coils for a null. The large 18 inch coil drives the input to the diff amp. The smaller coil ( also a diff coil ) is the TX. The "centre tap" of each diff coil was connected to analogue ground ... which in my configuration is +12 volts ( battery pos ).

The amp gain was 100 as in monocoil results.

This configuration is significantly more sensitive than the monocoil .... however it is now also more sensitive to ferrites as well as conductive targets ... the monocoil configuration is not very sensitive to ferrites.

The flyback decay is improved over the monocoil.

moodz


Green trace = output of diff amp ... gain = 100 ... not even overloading !!
White trace is MOSFET gate drive.

The coils as positioned for "null"

[WM6]

Very crude but here are the results of using induction balance using two differential coils.


The flyback decay is improved over the monocoil.


The coils as positioned for "null"

Crude really for us mono lowers. Can you post picture of signal response with some targets?

[Tinkerer]

This is basically an induction balanced DD coil configuration.

Present a crown cork in the vertical position to the coil and observe the points in time:
20us, 80us, 120us, 140us.

Present the crown cork in the flat position and observe the same points.

Keep the target at a distance that does not saturate the preamp.

Repeat the sequence above with your 1$ coin.

Have a lot of fun.

Tinkerer