Here is something I wrote a while ago that I hope will help you:
The quest for the perfect metal detector to this point has been quixotic. Minelab, has come the closest to building a fully submersible beach machine that can discriminate out iron in wet sand and saltwater. The “Excalibur” uses Broad Band Spectrum, or “BBS” technology, and retails for about $1,500.00. According to Minelab, their BBS operating system, “simultaneously transmits, receives and analyses a broad band of multiple frequencies to deliver substantial detection depth, high sensitivity and accurate discrimination for a wide range of target types.” The key takeaway here is “multiple frequencies.” Unfortunately, radio waves regardless of their frequency still have to be filtered and balanced in heavily conductive wet-ocean sand and highly mineralized saltwater. That limits the systems depth capabilities.
Single frequency VLF machines (Very Low Frequency), have even more limitations in the harsh saltwater environment. Take for example the Tesoro Lobo Super Traq. This VLF single frequency machine (17.9Khz) is one of the finest and deepest gold nugget finders on the market today. The Lobo Super Traq, is capable of finding BB-sized gold nuggets eight-inches deep in heavily mineralized ground, or a nickel in dry beach sand at 14-inches. Put that same nugget – or even the nickel, seven-inches deep in wet saltwater sand and the Lobo could walk right over it while chattering, or maybe without seeing it at all. Why?
The magnetic iron sands (“Black Sands”), salt, and high concentrations of other minerals in the water and sand conspire to bounce the radio waves away from the target. Conductivity and mineralization act like a shield around the target and create white noise that must be filtered electronically. Think of it as turning on your bright headlights in a heavy fog at night. All that powerful light is diffused and causes a complete white out – you can’t see anything three-feet past the hood of your car! However when you turn on your yellow fog lights, you can see a little further – not as far as you could in clear daylight, but further. That is why all radio wave machines must be “ground balanced” or tuned, to maximize their depth potential, and why BBS filters and multi-frequencies are so effective – yet still limited.
Unlike BBS and VLF metal detectors, which constantly send and receive thousands of low frequency radio waves per second, a Pulse Induction (PI) metal detector fires high-voltage pulses into the sand several hundred times per second. If no metal is present the electric pulse decays at a uniform rate with no anomalies. When metal is present a small “eddy” current flows through it causing the voltage decay time to increase, which creates a measurable anomaly. Unlike VLF radio waves, electronic pulses are impervious to the effects of conductivity and mineralization, and are unaffected by salt or black sands.
PI metal detectors give the user superior depth capabilities in all metal detecting situations and soil conditions. Using the same heavy fog at night metaphor that I referred to earlier, pulse induction is like headlights that cut completely through the fog as if it were not there at all. The trade-off for that added depth and clarity is the inability to discriminate, or block out iron targets that you generally don’t want to waste time and energy digging. While a pulse induction machine detects all metals without discrimination, the minute differences in the signal tone and quality can give a skilled and experienced operator a clue as to what the target may, or may not be.
Will one machine do it all? Not in my opinion. I always advise new beach metal detecting hobbyists to have a VLF machine for dry sand (as well as their other dirt detecting needs), and a PI machine for the water and wet-sand (and deep farm field and relic hunting). In truth, it all comes down to what you prefer and can afford. Good Luck!
