A
Anonymous
Guest
I posted this on the Finders Gold Forum, but the principles equally apply to coins and rings.
As previously explained, the metallic composition of gold nuggets has a dramatic effect on the detection range. Even 5% of other metal can give rise to more than 50% loss in detection depth. The other important factor is the surface area of the nugget as seen by the magnetic field emanating from the coil. There are certain basic laws of physics that apply to all electromagnetic detectors using coils whether PI, VLF or whatever. Simply put, the received signal is proportional to the cube of the target diameter. So, if you can detect a 1/4in diameter nugget at 8in, then a 1/2in diameter nugget (which is four times the area) will give 8 x the signal (2 cubed, or 2x2x2) of the 1/4in nugget. However, 8 x the signal only gives 1.4 x improvement in range, so the 1/2 in nugget would be detected at 1.4 x 8in, or 11.2in. Say we now had a 1in diameter nugget which is 16 x the area of the 1/4in, this will give 64 x the signal (4 cubed, or 4x4x4) which will give double the range i.e. 16in. This law is true only for objects which are small in relation to the size of the search coil. These results neglect any effect of the ground, which may well worsen the range at depth if it absorbs or distorts the signal. Remember also, that if your 1/4in nugget is pure gold and your 1in nugget is 95% gold and 5% other metal you may lose 50% of your range. In other words you can only detect the 1incher at the same range as the 1/4in. The moral is, if you are finding gold, be happy. Comparing ranges on nuggets of different sizes, shapes and compositions in different types of ground is fraught with problems.
Eric.
As previously explained, the metallic composition of gold nuggets has a dramatic effect on the detection range. Even 5% of other metal can give rise to more than 50% loss in detection depth. The other important factor is the surface area of the nugget as seen by the magnetic field emanating from the coil. There are certain basic laws of physics that apply to all electromagnetic detectors using coils whether PI, VLF or whatever. Simply put, the received signal is proportional to the cube of the target diameter. So, if you can detect a 1/4in diameter nugget at 8in, then a 1/2in diameter nugget (which is four times the area) will give 8 x the signal (2 cubed, or 2x2x2) of the 1/4in nugget. However, 8 x the signal only gives 1.4 x improvement in range, so the 1/2 in nugget would be detected at 1.4 x 8in, or 11.2in. Say we now had a 1in diameter nugget which is 16 x the area of the 1/4in, this will give 64 x the signal (4 cubed, or 4x4x4) which will give double the range i.e. 16in. This law is true only for objects which are small in relation to the size of the search coil. These results neglect any effect of the ground, which may well worsen the range at depth if it absorbs or distorts the signal. Remember also, that if your 1/4in nugget is pure gold and your 1in nugget is 95% gold and 5% other metal you may lose 50% of your range. In other words you can only detect the 1incher at the same range as the 1/4in. The moral is, if you are finding gold, be happy. Comparing ranges on nuggets of different sizes, shapes and compositions in different types of ground is fraught with problems.
Eric.