Chris I think what they are saying in 1.1.3 is the Explorer not only transmits 'a' square wave which itself consists of several orders of harmonic frequencies but multiple square waves each with its own harmonic frequencies. When you look at the Explorer transmit signal on the scope you see basically two different square wave frequencies being transmitted, a long and a short in a repeating pattern, dot dot dot dash dash dash repeat. I don't know what the two base frequencies are, its highly likely they were chosen to give the machine the best of what a lower frequency can offer and what a higher frequency can offer. Higher frequencies have certain advantages and disadvantages, but don't get as much depth. Lower frequencies have certain advantages and disadvantages but go deeper. The Explorer tries to give you both in a single machine. So the two square waves effectively provides the Explorer with 28 frequencies of information, what they do with that information inside the machine is a mystery to me, the software and circuitry is where the Explorer magic happens. I had an engineer tell me once he thinks the Explorer has some elements more common with pulse induction detectors which compared to a VLF detector its like most soil isn't even there. That kind of makes sense since Minelab's high end gold detectors are pulse induction. I have also heard the soil over in Australia where Minelabs gold detectors are born is horrible, its so bad its almost a metal. In head to head comparisons in the field, on deep targets before they are dug the Explorer gets more depth and produces more accurate ID's vs the best VLF detectors. It has its limits, its no pulse induction machine and the Explorer will choke where we have heavy concentrations of volcanic black sand here in the Pacific Northwest but its better than the VLF's.
2.9 'may' be speaking to that pulse induction like behavior in the Explorer. Keeping in mind I'm no pulse induction expert but in pulse induction they are dealing with decay, the eddy currents induced in a target decay at different speeds depending on the target. Soil which produces by far the strongest signal also decays the quickest for the most part and so the timing of a pulse induction machine is tuned to allow the ground to decay and vanish before sampling for targets. Some targets like small gold also decay very quickly, iron decays slowly. So if you can get rid of the ground portion of the signal then the rates at which the eddy currents in a target are decaying tells you something about that object. Again I'm a rank amateur in my understanding of pulse induction and I know squat about the mysterious inner workings of the Explorer software and circuit. But it sounds logical that if they can get some pulse induction type of information out of the Explorer this would be useful right.
