Minelab Equinox 800 vs Simplex / multi vs single freq

[tragac]

Please share your opinions and experience for example using EQ 800 and Nokta Simplex or any multi freq detector vs
single freq detector

Is it any real advantage of multi vs single freq
What difference in depth if used multi vs single freq

[Carl-NC]

A key advantage of MF is the ability to cancel salt water. Another advantage should be better target ID and better iron ID. A disadvantage of MF is that specific targets can be detected slightly deeper in a SF mode than in MF mode, but MF mode should give an overall more even depth across different targets. As an example, here are some numbers for the White's V3 for a low conductor and a high conductor:

Target	2.5kHz	22.5kHz	MF
Nickel	8"	10"	9"
Quarter	10"	8"	9"

These are illustrative numbers only, I don't know what the real depths are.

[Melbeta]

That is an interesting illustration. I was not aware of that particular advantage and disadvantage, when comparing MF with SF. I am going to post a copy of a wet sand test and a black sand test, done by Chief Engineer John Earle, and other Compass Electronics engineers, at a site where the salt water was a good place to test along with black sands. In addition, other engineers, not from Compass Electronics, but obviously friends of each other, also brought their own (other brand names) of models, to test along with the Compass models. Now this is years ago, with older vintage machines, not competitive with today's models. It is just for information illustration.

Now keep in mind, that Chief Engineer John Earle, left Compass Electronics, and went to work in the 1990s as Chief Engineer capacity, at Whites Electronics, after this test period, and of course, even Whites Electronics in today's time period, is no longer in business, and has now become the property of Garrett Electronics. Now I am not aware of how many Chief Engineers an manufacturer will employ, but John Earle took his experience and expertise with him, and worked on many successful metal detector models at Whites Electronics, while it was still in business back then. So times change, models change, but we know the black sands and the wet sands, both salt water wet and regular water wet, are still with us today... And now today, we do have Multi-Frequency and Single Frequency models, still out there, detecting, and competing for our purchase dollars...

Well, I give up, I cannot get this John Earle file, to be entered for uploading into this forum. It just will not upload.
Melbeta

[tragac]

Thank you on answers.
It looks that MF's only advantage is for beach searching and that MF is not of big advantage for searching
on posture and can have real disadvantage because of reduced
depth detection.
Also there is another question is it MF detector able to detect
target on same depth if used only one same freq like SF detector with
same search coil.

Is it also any advantage for infested terrain. ..

[Qiaozhi]

Well, I give up, I cannot get this John Earle file, to be entered for uploading into this forum. It just will not upload.
Melbeta

You will need to compress the file using zip or rar, if it's not a file type recognized by the forum.
If you're still having trouble, then email it to me and I'll post it.

[Carl-NC]

It looks that MF's only advantage is for beach searching and that MF is not of big advantage for searching
on posture and can have real disadvantage because of reduced depth detection.

Not necessarily. I gave you an example of how one MF detector behaves. Minelab BBS (Sovereign, Explorer, etc) is well known for being exceptionally deep on silver coins, better than many SF detectors. That's because it primarily runs at 3.125kHz, and its 2nd frequency (25kHz) is relatively weak. Therefore BBS was not very good at detecting low conductors but exceptional at deep silver. Also, I have not done any testing with the latest MF designs (Equinox, Vanquish, Apex) so I don't know how they behave. And, done right, MF can potentially do a better job in iron trash.

Also there is another question is it MF detector able to detect target on same depth if used only one same freq like SF detector with same search coil.

If you put an MF detector in (true) SF mode then, yes, it should perform as good as a SF detector running the same frequency.

[Taktyk]

Interesting that no one has taken measurements at different frequencies in multifrequency mode . But ones that have identical current...

[tragac]

Good point, that was also my question.
Are all those up to today really multy frequency detectors...

[Taktyk]

It is best to take frequencies from 2 to 50kHz and metals by conductivity scale: https://www.researchgate.net/figure/...tbl1_265214805
Since the real DSP process is for 2-3F, for the implementation of ground filters and amplitude measurement and phase. 2-25-50kHz. Measure the results for different distances from the coil 5-10-15-20-25-30 ... cm. Further understand and leverage through machine learning. Relationships should be seen in a neural network.

[Taktyk]

Good point, that was also my question.
Are all those up to today really multy frequency detectors...

Everyone is different, the MF detector is a different machine in each case...

[Altra]

Here are some photos of the Equinox Tx and dual frequency DFX. On an interesting note when the Equinox is set to single frequency mode the Tx voltage increases with frequency. The 5khz has the lowest tx voltage while the 40khz has the highest.

[Taktyk]

Here are some photos of the Equinox Tx and dual frequency DFX. On an interesting note when the Equinox is set to single frequency mode the Tx voltage increases with frequency. The 5khz has the lowest tx voltage while the 40khz has the highest.

This is increasing the current for a higher frequency waveform. It has to be done right to go further. Further analysis can only be in a multidimensional matrix where the amplitude, phase of each F is considered.

[Altra]

If you look at my DFX photo of the unfiltered pre-amp out. You can see the fundamental (2.9khz) has two to three times the amplitude as the superimposed 5th harmonic (14.7khz). So for a given coil the frequencies need to be equalized to process the signal. I built a dual frequency circuit that worked well rejecting salt water and feO2. High sensitivity to high conductors. But it suffered lower sensitivity to gold. I need to revisit the project and increase the gain on the harmonic channel and maybe reduce the gain on the fundamental.

[Carl-NC]

For a better visualization of what's going on in a MF design always plot the coil current, not the coil voltage:

[Taktyk]

For a better visualization of what's going on in a MF design always plot the coil current, not the coil voltage:

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If 100mV = 100mA then 'EqProsp' is approximately 600mApp for 40kHz. But 'Equinox' has what amplitude App?