metalman709 said:
okay... i had my heart set on the at pro but have been looking at other posts about other water machines in the same price range and now i'm confused....came up with 3 different machines and all have their pro's and con's....being a tesoro user i'm torn between the sand shark, the tiger shark, and the at pro....i will post this same topic in the tesoro topic for discussion as well.....mainly will be hunting fresh water seeing as i live in georgia but once or twice a year will be in salt conditions and on land....which would you choose and why
?
Hi MM! The key is understanding the differences between "VLF," and "PI" machines and what they can do (and can't do). The "Tiger Shark" (and the AT PRO) is a VLF metal detector, and the "Sand Shark" is a PI detector.
The VLF metal detector sends 12,000 - 60,000 radio waves per-second into the ground. When the radio waves hit something conductive - like an iron nail, gold ring, coin or aluminum pulltab, a magnetic field sets up around the object and a particular signal frequency is transmitted back to the detector's receiving coil. VLF metal detectors have the ability to "discriminate," or tell what type of metal they are seeing by "reading" the return signal frequency. An iron nail for example, has a different frequency than a silver coin. The processor in the metal detector knows the difference between the two, and can be set to remain silent when seeing the nail. However, the radio waves bounce off everything that is conductive in the sand or water. This is why VLF detectors must be "ground balanced" to work effectively in highly mineralized soil, or on highly conductive saltwater beaches. You must tune or adjust the machine to see through the "fog," or white-noise created by the salt and iron in the sand or water you are detecting. Unfortunately, this usually leads to a loss of depth and stability with most VLF detectors.
A pulse induction or, "PI" metal detector, sends out hundreds of electric pulses-per-second, rather than thousands of radio waves. While PI metal detectors do not have the ability to discriminate between different types of metal, their powerful pulses go much deeper than the VLF signal, and eliminate the problem of mineral conductivity. A pulse induction detector measures the decay rate of the electronic pulses it sends out, and looks for anomalies. The strong electronic pulse is not conducted by the salt in the water or the iron in the black sands. Think of a Navy ship "pinging" with its sonar for an enemy submarine. If there is nothing in the water the "ping" just continues on and fades out at the same measured rate. If the submarine is there, the signal decay is interrupted and bounces back to the sonar operator on the ship.
Most successful ocean-beach detectorists, own both types of detector. The land-based VLF unit is preferred in the dry sand blanket area because you can use discrimination to knock out iron and still achieve superior depth without loss of stability. The pulse induction machine is used on the wet ocean- and black- sands, as well as in the surf.
Hope this helps!
