Minelab Multi-IQ vs Multi-IQ+, or why X-Terra ELITE and EQUINOX coils don't work on the Manticore

[Byko]

Minelab Multi-IQ vs Multi-IQ+, or why X-Terra ELITE and EQUINOX coils don't work on the Manticore

Several people have asked what the "+" in Multi-IQ+ means. Others are unhappy that their X-Terra ELITE and EQUINOX coils don't work on the Manticore.

Yesterday I watched two videos that captured the TX waveforms of all three detectors. From them I concluded that, on the Manticore, the "+" most likely means the TX current has been roughly doubled.

The numbers support this. The received target signal is proportional to TX current, so doubling the current doubles the signal. For a small target, the induction-balance response falls off roughly as 1/d⁶ with depth. So twice the signal gives about 2^(1/6) ≈ 1.12 times the depth, or about 12% more sensitivity. The cost is battery life, because TX power grows roughly with the square of the current.

This also explains the coil incompatibility. A coil designed for the Multi-IQ TX drive level and impedance can't simply be used on a transmitter that runs about twice the current.

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Minelab TX coil drive: X-Terra Elite vs Equinox 700 vs Manticore (scope readings from two lovecpokladu.cz videos)

The Czech site lovecpokladu.cz published two videos in which they scope the TX coil of three Minelab Multi-IQ
detectors. I transcribed and translated the Czech narration and read the scope screens frame by frame. Below is
only what is directly measured or shown on screen. No estimates.

SETUP (both videos)
- Scope: UNI-T UTD2025C.
- Access: a coil-connector T-adapter, so neither detector is opened.
- Signal: the single shielded pair in the coil cable is the TX. The author says the TX coil is driven straight
from the detector, while the RX signal is processed inside the coil. This agrees with Skippy's finding of an
in-coil RX preamp:

https://www.geotech1.com/forums/forum/technology/coils/15888-ml-equinox-coil-discussion-thread

TX DRIVE LEVELS (flat level from zero, read with the author's own scope cursors, video 2)
- X-Terra Elite, own coil ........................ +9.0 / -9.2 V (+/-8.8 V in the later Manticore capture)
- X-Terra Elite with an Equinox coil ............. +/-9 V, unchanged
- Equinox 700, same Equinox coil ................. 12.2 V (flat)
- Manticore (its own coil; the author says the coil parameters differ) ... +22.0 / -22.4 V
- Ratios from these numbers: Equinox / Elite = 1.36x; Manticore / Equinox = 1.8x.

SPIKES AT THE SWITCHING EDGES (on screen)
- X-Terra Elite: about +18 V (10 V/div).
- Equinox 700: goes off the top of the screen, so at least +20 V (5 V/div).
- Manticore: goes off both edges of the screen, so at least +/-40 V (10 V/div). True peaks not measured.

VIDEO 1 (workshop bench, Equinox 700 vs Manticore, one channel)
- The probe was set to x10 with the scope channel at x1. The author says so and switches it on camera at 2:37,
so every value on screen in that video is 10x low.
- Equinox 700 (probe switched to x1): 55 V peak-to-peak, 11.7 V RMS.
- Manticore, same probe and settings: peak-to-peak and RMS both about 2x the Equinox ("instead of 5 I have 10,
instead of 1 I have 2").

WAVEFORM
- Bipolar, multi-level PWM with segments of roughly 7-46 us. Not a sine and not a plain square wave.
- No ringing is resolved after the edges. The fastest timebase in either video is 10 us/div (about 0.4 us per
display column), so the TX self-resonance cannot be measured from these videos.

RELATED MEASUREMENTS BY OTHERS
- Stock EQX 11 TX coil: L = 119 uH, R ~0.35 ohm (Skippy):

https://www.geotech1.com/forums/forum/technology/coils/15888-ml-equinox-coil-discussion-thread

- Multi-IQ tones, Equinox 600/800 (Carl Moreland, quoted on DetectorProspector):

https://www.detectorprospector.com/topic/25904-so-the-x-terra-elite/page/2/

Park/Field 2.6 + 7.8 + 39 kHz; Beach 2.6 + 7.8 + 23.4 kHz.
- Skippy gives 7812.5 / 18229.17 / 39062.5 Hz, i.e. the 3rd, 7th and 15th harmonics of 2604.17 Hz:

https://www.geotech1.com/forums/forum/technology/tech-forum/15003-minelab-equinox-challenge

ATTACHED IMAGES (one per detector; perspective-corrected frames straight from video 2, annotated)
- X-Terra Elite:
Minelab X-Terra Elite - TX - video2 bJMA0DrmV04 3m45s - own coil - 5 V-div 50 us-div (annotated).png


- Equinox 700 (blue) vs X-Terra Elite (yellow):
Minelab Equinox 700 (CH1 blue) vs X-Terra Elite (CH2 yellow) - TX - video2 bJMA0DrmV04 7m30s - same Equinox coil - 5 V-div 20 us-div (annotated).png


- Manticore (blue) vs X-Terra Elite (yellow):
Minelab Manticore (CH1 blue) vs X-Terra Elite (CH2 yellow) - TX - video2 bJMA0DrmV04 11m10s - 10 V-div 10 us-div (annotated).png


LINKS
- Video 1, Manticore / Equinox power difference on the TX coil (2023-01-30): https://youtu.be/RjNb2Tj6jCs
- Article for video 1: https://www.lovecpokladu.cz/en/home/...ting-coil-9363
- Video 2, performance comparison of the new Minelab multi-frequency series (2024-06-21): https://youtu.be/bJMA0DrmV04
- Article for video 2: https://www.lovecpokladu.cz/en/home/...or-series-9825
- Geotech1, ML Equinox coil discussion thread (Skippy's coil measurements):

https://www.geotech1.com/forums/forum/technology/coils/15888-ml-equinox-coil-discussion-thread

- Geotech1, Minelab Equinox challenge (Multi-IQ tones):

https://www.geotech1.com/forums/forum/technology/tech-forum/15003-minelab-equinox-challenge

- DetectorProspector, "So, The X-Terra Elite", page 2 (Carl Moreland's tone measurements):

https://www.detectorprospector.com/topic/25904-so-the-x-terra-elite/page/2/

- Minelab Multi-IQ Technology Explained (Steve Herschbach / Minelab Treasure Talk):

https://www.detectorprospector.com/magazine/best-of-forums/minelab-multi-iq-technology-details-explained/

Enjoy

[Carl-NC]

This also explains the coil incompatibility. A coil designed for the Multi-IQ TX drive level and impedance can't simply be used on a transmitter that runs about twice the current.

Sure it can. All of these coils are driven by an H-bridge circuit; you can easily double the voltage on the H-bridge and double the TX current with no problem*. In fact, some detectors (White's V3i, Quest V80) have a TX Boost feature whereby you can increase the TX drive. On the V3i, it was a 3X boost. Yes, it burns more power. The power loss is almost entirely in the TX-R of the coil as most of the coil energy is recycled in a big supply cap, so a low TX-R is important, especially at low frequency where XL is small.

Here are the TX coil measurements from 3 Minelab models, sorted by age:



Even though all 3 models use about the same frequency ranges, over time Minelab has increased the TX-L (Note: I would like to know the parameters for the Eq900; I would expect its TX-L to be 150uH like the XT-Pro). For all practical purposes, the TX-R has remained about the same. In reality, any of these coils will work on any of the models with very little difference in performance. The only reason they cannot is because ML has put an ID chip in the coil that prevents its use in a different model. The reason for doing that is to sell more coils.

But otherwise, there is no reason why a common coil design could not have been made for all these models. Besides selling more coils, only reason for making a coil incompatible is if you want to cover a different frequency range. Ferinstance, if you want a super-low frequency coil (1kHz-10kHz) you would increase the TX-L and decrease the TX-R, which means more wire of a fatter gauge, which means a heavier coil. If you want a super-high frequency coil (50kHz-120kHz) you would decrease the TX-L and use fine-stranded litz.

* As long as the coil null can handle it.

[JoyJo]

Equinox uses a semi-bridge in the Tx cascade. Vankvish is a full bridge. But I didn't see the board close to the manticore to look at. Some photos show that 4 large electrolytic capacitors and one chip in the soik8 body are installed in the manticore (apparently this is an assembly of two MOSFETs). Therefore, I assumed that the scheme in the manticor is similar to the scheme of the fisher cz in which a half-bridge of two MOSFETs controls the TX coil, the second end of which is connected to the midpoint of 4 electrolytic capacitors.

[JoyJo]

[Carl-NC]

Whether half-bridge or full-bridge doesn't matter, same results.

[JoyJo]

Interesting. Is there a photo of the manticore board in good quality somewhere? So that it could be better considered. The reception part in the manticore, judging by the photos I have, as well as in Equinox, is built on the audio codec pcm1864 (or 1860, I don't remember exactly). According to the photo, the binding is the same. But the TX cascade is different. In the equinox, the supply voltage of the TX cascade was about 28-29V. I wonder what the supply voltage is in the manticore. It seems to me that it is not quite reasonable to pump out of a 29V lithium battery from one.

[Byko]

Carl, thanks. Those L/R numbers correct my post: it is not twice the current.

The Manticore drives 1.8x the voltage (22 V vs 12.2 V), but into 1.7x the inductance (174.5 vs 103.7 uH).
The segments are 10-45 us against L/R of about 200-300 us, so the current ramp goes as V/L:

- TX current, Manticore / Equinox 700: about 1.07x (1.23x with Skippy's 119 uH)
- Ampere-turns, assuming the same 11" DD geometry, so N*I ~ V/sqrt(L): about 1.4-1.5x

The second figure is close to Minelab's "up to 50% more power". I agree the coils are not that different electrically.

[EL NINO]

It would be interesting to add coils from Eq 900, and X Terra Elite..
I heard some opinions..that the coil from Equinox 900 works better on Equinox 800 than the original coil..