Induction Balance Stuff - Single/Multi Frequency Response, GB, Disc, Measurements, Ideas, Fun, etc.

[moodz]

I have a coil for a Minelab Vanquish that uses a square wave signal.

The CC coil drives a semiresonant coil. The CC is required to boost the TX current. If you just use a purely resonant coil ... its a big mistake - you've lost your reference.

[moodz]

Below is the ground balance in operation.

The polar plot on the left shows the target responses ( this real live data from the detector ).
The T buttons allow me to save the responses.
The polar plot on the right shows the IGB ( instant ground balance ) applied to the same data.

Yup there is no free lunch ... you lose some target strength ( esp the silver ring purple trace ... because it is almost in the same angular plane as the ferrous ground )
However the ground is almost knocked down to zero ( right plot )

Of course this is only one frequency ... and we are only using 15% of the H7 CPU cycles. :-)

[Marchel]

The CC coil drives a semiresonant coil. The CC is required to boost the TX current. If you just use a purely resonant coil ... its a big mistake - you've lost your reference.

The TX circuit is based on the XP Deus 2 FMF coil and their coil works well and achieves very good results so I think it will work well.

[moodz]

The TX circuit is based on the XP Deus 2 FMF coil and their coil works well and achieves very good results so I think it will work well.

XP DEUS II transmit waveform ... looks kind weird. Unless you have their algorithm life will be difficult. What we can say is that thier coil is not resonant.

[Marchel]

XP DEUS II transmit waveform ... looks kind weird. Unless you have their algorithm life will be difficult. What we can say is that thier coil is not resonant.

I have all the XP deus 2 signal waveforms recorded with an oscilloscope so I saw all the RX and TX waveforms, it would be great to see your RX and TX wiring diagram if it's not secret.

[moodz]

its almost exactly as per this post ... which I made some time ago. https://www.geotech1.com/forums/foru...uit#post412997

The only difference is the primary of the pulse transformer is capacitor isolated so when the switch is powered but no drive pulses DC is blocked.

I have tested it from 4 khz to 96 khz and still getting 1 amp square wave at 96 Khz or 100 volt peak sine wave at 96 Khz. ( my whole circuit draws 250 mA from the 12 volt drill battery 2.5 AH lasts several hours )

The transistors are from LTSPICE ... I used better ones. The pulse transformer has to match your TX coil. ( some design / experimentation required )

[moodz]

The reciever is just the coil connected to the input ADC with a 0.1 uf cap and a 1.6 volt bias to keep the ADC happy.
On my 40 cm IB coil the receive voltage is 20mv peak ... so I will be fitting a 50X low noise amp .. but at the moment I get good results with no amp fitted as you can see.

[Marchel]

I looked at your coil concept and it also looks good, in my case when I use Minelab coils and XP Deus I cannot use your SPLL method because I cannot get a pRX reference signal.

[Aziz]

The reciever is just the coil connected to the input ADC with a 0.1 uf cap and a 1.6 volt bias to keep the ADC happy.
On my 40 cm IB coil the receive voltage is 20mv peak ... so I will be fitting a 50X low noise amp .. but at the moment I get good results with no amp fitted as you can see.

I also don't need any pre-amp. 50 mA - 100 mA peak current to the TX coil is even enough.

[moodz]

I also don't need any pre-amp. 50 mA - 100 mA peak current to the TX coil is even enough.

Not if you've got worms.

[Marchel]

Do you resample the signal from the ADC somehow or does it go directly to the SPLL ? or is it still filtered through some filters ?.

[Aziz]

Not if you've got worms.

But this is not what I feed into the LC tank. With Q=10, only 1/10 of the current will be fed into the LC tank. I usually have Q up to 40 or 60.
This is much more power efficient. But there is a practical limit of TX current:
The settling time until the parts of the LC tank don't temperature drift.

[Marchel]

I would also like to know which values you send via USB to your application, whether just I and Q or directly the values from the ADC and the application on the PC demodulates them directly.

[Aziz]

Hi all,

I have switched back to mono coil VLF and have tested the SPLL algorithm. It is really working very nice.

Now watch out! This is very strange. Can't say, why this is working:
It simplifies the GB method with a chirp modulation around the resonant frequency fr:
f from fr-100 Hz to fr+100 Hz, where fr=resonant frequency, f=stimulation frequency
No more vector rotation required. Ferrite ground (hot mineral ground) gives +90 ° angle (dQ-Axis). So the resistive response is directly projected to the dI-Axis.
The dI-part can be used to detect targets.

This is the most simple mono coil VLF ever. It doesn't need ground balance anymore (inherent built-in).
Mission accomplished for mono coil VLF.

So what is going on? Why it is working? I don't know.
Cheers

[Aziz]

Oh well,

I had a good series of starting conditions. Pure by chance. The ferrite response was always in the Q direction.
Now it isn't anymore. We need the vector rotation for GB. But this isn't any issue.