Minelab Equinox Challenge

[Qiaozhi]

Quote:"While mowing the grass"
What kind of grass do you have on your lawn? It's making you creative.

How are you determining 'Power' , when there's no resistive object in your model to get hot?

The coil has a series resistance of 1ohm. It's not shown on the schematic.
V1 is a zero-volt voltage source (a shortcircuit) that's used to monitor the coil current. This is used as input to the H element (current-controlled voltage source). Then an E element (voltage-controlled voltage source) has an attached polynomial that multiplies the voltage at the X node with that at the Y node to calculate power. The graph facility will then let you run an FFT on the Z node.

[Qiaozhi]

What kind of grass do you have on your lawn? It's making you creative.

I've just got your meaning after a short temporal delay!
It wasn't "wacky baccy", if that's what you meant.

[bklein]

Sorry to be off topic a bit here but say you do use a 1 ohm resistor in place of the TX coil. Would a CTX or Equinox still "run"? I'm wondering if then you could get a more accurate TX waveform. Also, another wacky idea, if the detector still runs (no "no coil detected" error or similar), could you experiment with your own TX drive circuit to actually drive the TX coil? (Does the rx circuitry/code need to synchronize with the TX signal?

[Qiaozhi]

It seems to me that the power calculation represents the amount of power lost in the resistive element of the coil, which happens to coincide with the frequencies shown in Minelab's marketing blurb for the Equinox. Whereas the radiated magnetic field is actually dependent on the current. In this case the peaks in the FFT do not match up, so what gives?

Clearly there is no mistake in deriving the Multi-IQ transmit waveform from Carls' current measurement, as the waveform published by Minelab matches exactly the one shown in post #28.

It still looks like the real frequencies are 7.8kHz, 18.2kHz and 39kHz.

[Skippy]

Maybe you didn't see my post in the main Nox thread, but it appears Beach1&2 modes use 7.8kHz and 23.4kHz. We're waiting on better data, there may be other alternative freqs in other modes.

[Carl-NC]

Maybe you didn't see my post in the main Nox thread, but it appears Beach1&2 modes use 7.8kHz and 23.4kHz. We're waiting on better data, there may be other alternative freqs in other modes.

Could be, I only got a short time to look at the 800, and only in Park mode. 39kHz is too high for beach, 23k is usable.

[bklein]

Beach 2 has TX power cut back. A lot quieter in the wet/water. Just not many targets there right now.

[green]

Added target and Rx coil to Qiaozhi's spice model. Wondering if it makes sense. Think can't use a antialiasing filter with a PI but would want to use one to process these signals?

[Qiaozhi]

Added target and Rx coil to Qiaozhi's spice model. Wondering if it makes sense. Think can't use a antialiasing filter with a PI but would want to use one to process these signals?

The Minelab Equinox is not a PI, so putting a damping resistor across the coil is not much use. I assume the RX coil is not tuned, and they filter and process each frequency separately.

[green]

The Minelab Equinox is not a PI, so putting a damping resistor across the coil is not much use. I assume the RX coil is not tuned, and they filter and process each frequency separately.

I used 2 ohms and 200p for the Rx coil. Would have added to schematic but forgot how. I would think the coil would oscillate without a damping resistor.

I was thinking they would use a antialiasing filter, sample the signal with an A-D then filter and process the signal with software

[ivconic]

https://pubs.acs.org/doi/abs/10.1021...cromol.6b00428

[dbanner]

[green]

http://www.geotech1.com/forums/attac...0&d=1525999207

The current trace looks like it is constant rate. I'm thinking if coil is switched with a H bridge it probably wouldn't be perfect. Does it need to be constant rate? Some scope pictures showing what happens if it isn't. IB coil with ground as target. Rx signal is flat with current constant rate. Amplitude is proportional to rate so drops off as rate decreases when not controlled due to PS droop, switch and coil resistance.

[Qiaozhi]

Using the attached Minelab patent, I was able to calculate (and confirm by simulation) that using Fa = 2.5kHz, Fb = 7.5kHz, Fc = 10kHz and Fd = 30kHz, results in a frequency spectrum with F1 = 5kHz, F2 = 10kHz, F3 = 20kHz and F4 = 40kHz. Also, all of these frequencies have equal amplitude. This is with option 1.

Using option 3: Fa = 7.5kHz, Fb = 12.5kHz, Fc = 15kHz and Fd = 25kHz yields a frequency spectrum with F1 = 5kHz, F2 = 10kHz, F3 = 20kHz and F4 = 40kHz. The same as with Option 1.

However ... how you can use this method to create a frequency spectrum with 5 frequencies currently has me puzzled.

[ivconic]

... by taking all the possible harmonics into account too...