Jason is partially correct. FBS doesn't do anything close to the impression the marketing language leads one to believe. It does in fact only transmit and receive 2 fundamental frequencies, and the same two (3.125khz and 25khz). It doesn't transmit a broad range of fundamental frequencies and pick from the best. Rather, it transmits those same two over and over in ratios that favor the 3.125khz frequency and utilize the halflife of that frequency for analysis. This is why FBS machines are so hot on silver and not so hot on small gold that even some 13-15khz machines do a better job of sniffing out. The 28 frequency claim and the full band from 1.5khz to 100khz is by now well known marketing sleight of hand for those that have been paying attention. It was first discovered by Carl Moreland and verified by others in the field. Minelab was counting harmonics among its transmitted frequencies that are neither received nor processed by the machines. multi-IQ does something different. It is more balanced and effective over the spectrum of conductors. It weights it's signal to the task at hand. Rather than limiting itself to the same two frequencies with a bias toward deep, high conductors, you'll find that in the Gold mode for example, the signal is heavy on the 20 and 40khz frequencies. You'll find that on beach mode it is heavy on the 5 and 10khz as lower frequencies handle those conditions better. It's a smarter way to do multifrequency. It chooses the best or most effective fundamentals in each scenario. Both FBS and Multi-IQ utilize multifrequency in an automated sequence. Frequencies are rapid fired in a pulse like sequential manner, rather than simultaneously in the most literal sense. It's worth noting that it definitely seems to be a more efficient way of doing things as it loses no real depth over single frequencies. In fact, it could be said that Minelab multifrequency methods produce superior depth results over most single frequency machines.
