Virtually all simultaneous multi frequency technologies from the 1990s to now have been proven to work better than single frequency VLFs at salt water beaches.
FBS/FBS2 has been proven to work extremely well on higher conductors in mild to moderately iron mineralized ground also, even on deep high conductors. However, all of the previous SMF tech has suffered from less accuracy on deeper non-ferrous lower to mid conductors, very small sub gram targets and ground balance issues in moderate to high iron mineralization along with being extremely slow on target recovery speed. Many single frequency and selectable single frequency detectors perform just as well in mild to moderate iron mineralization or better especially on non-ferrous low conductors, very small targets and some have extremely fast recovery speed in comparison.
Then Minelab came out with Multi IQ. Multi IQ on the Equinox compared to the Equinox selectable single frequencies does offer a big advantage in target ID accuracy and depth on the full range of non-ferrous target conductivity in all ground conditions except for the absolute worst where a pulse induction detector is the only choice. It is also excellent on sub gram non-ferrous targets of any conductivity. Multi IQ on the Equinox also offers much better target recovery speed than any SMF detector produced until Deus 2.
I have posted this explanation of what Multi IQ does in a very simple way as explained by Minelab's lead physicist for Multi IQ several times. Some here simply cannot or do not want to believe these words:
Simultaneous Multi-Frequency In-phase and Quadrature Synchronous Demodulation.
“For each frequency the detector transmits and receives there are two signals which can be extracted which we refer to as I and Q. The Q signal is most sensitive to targets, while the I signal is most sensitive to iron content. Traditional single-frequency metal detectors use the Q signal to detect targets, and then use the ratio of the I and Q signals to assess the characteristics of the target and assign a target ID. The problem with this approach is that the I signal is sensitive to the iron content of the soil. The target ID is always perturbed by the response from the soil, and as the signal from the target gets weaker, this perturbation becomes substantial. With some simplification here for brevity, if a detector transmits and receives on more than one frequency, it can ignore the soil sensitive I signals, and instead look at the multiple Q signals it receives in order to determine a target ID. That way, even for weak targets or highly mineralized soils, the target ID is far less perturbed by the response from the soil. This leads to very precise target IDs, both in mineralized soils and for targets at depth.”
After using the Equinox regularly in really bad iron mineralization since it was first released along with using it in milder ground and at saltwater beaches, I can only support what Dr. Warlich wrote. In the ground I detect in, using the Equinox in single frequency makes the Equinox only average at best and turns it into an X-Terra 705 but with more frequency choices, no coil swaps needed and faster recovery speed. Target ID accuracy suffers big time with different target IDs in each frequency along with severe instability and up-averaging on deeper targets.
Using the Equinox in Multi in 50 tones is the best way to experience how accurate it is as far as numerical target IDs. Using it in Multi in 5 tones makes the numerical target IDs a little less accurate but in either mode, if the target is a non-ferrous low, medium or high conductor, the audio and numbers will reflect the target's conductivity down to the depth of detection if the Equinox is using the multi setting.
If you read the quote above, it is easy to understand that ferrous targets are the Achilles heel of the Equinox which is why Minelab updated the iron bias settings for multi frequency use twice on the Equinox.
Two other factors are EMI and surface targets.
All SMF tech detectors can suffer from susceptibility to EMI. The Equinox is no exception. Its Noise Cancel feature is really a noise reduction feature. If EMI is present and if an Equinox is running in Multi with its sensitivity too high for the EMI conditions, the EMI will produce actual tones and target IDs which can effect actual target ID accuracy.
Also, the Equinox in Multi or selectable single frequency is a very high gain detector using a DD coil. Targets that are on or near the surface will be detected in all of their glory including changes in surface height, fluting on coins, threading on screws, bolts and aluminum screw caps, crimping on crown bottle caps and the different alloys within metals. A variety of target Ids can result between the center of the coil and its edges. When I am air testing, in a tot lot or just cherry picking shallow targets, I keep the coil well off the ground, lower the sensitivity and use a smaller coil like the 10X5" Coiltek. Target IDs are much more accurate this way.
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