Goldquest SS Coil Comparisons.
Posted By: Eric Foster <Beachscan@aol.com> (ACB7915F.ipt.aol.com)
Date: Tuesday, 24 September 2002, at 4:00 a.m.
I recently had some requests to make some 8in coils for the SS, in addition to the standard 11in that is normally supplied. A smaller the coil is useful in areas where there are rocks or vegetation, which make the use of larger coils difficult or even impossible. Also, it gives more precise separation of close targets, sharper pinpointing, and less ground signal in areas with iron mineralisation.
The interesting question, though, is what do you sacrifice in terms of detection range? Generally, the requests for a smaller coil have come from persons wishing to use the SS for nugget hunting, where conditions are rather different from those encountered in beach searching.
The results are interesting and fall broadly in line with the range curves for different coil sizes that I posted recently. All of the tests, except one, were conducted with gold nuggets that originated in Victoria, Australia. The exception was a gold ring, which was used to give a larger area target.
Initially a 0.1gm flat nugget was tested but was not detectable at any range. This is because the decay time of the signal was faster than the 10uS sample delay used in the SS.
0.4gm flat----------3.5in (8in coil)---2.5in (11in coil)
0.5gm irregular--2.5in---------------2.5in
0.9gm flat---------6.0in---------------6.0in
2.0gm flat---------7.0in---------------7.25in
3.6gm irregular--7.5in---------------8.0in
3.4gm 22k ring---13in----------------15in
All the tests, except the last one, were done by stacking plastic blocks on the coil and sliding the nuggets horizontally on the surface of the top block. This gives a more accurate figure than just using a ruler and holding the target manually. The audio was a just discernible, but clearly identifiable, change. The ring was done manually with a ruler for lack of enough blocks. Another inch could possibly be added to the ring for a just discernible signal.
The results show that, for small nuggets the 8in coil in not much different in range to the 11in coil, and at the lower end starts to win out. The 0.5gm irregular nugget shows less range because of its convoluted shape and maybe different composition. In fact it should be born in mind that the variation in composition of nuggets from different locations can result in widely differing detection ranges. The 3.4gm ring demonstrates that the radiating area of an object has a great effect on range and that the large coil then shows a distinct advantage. Both size coils are wound for the same inductance, which means that the 8in has a few more turns. This helps to some degree in making up the loss in range due to the difference in diameter, which likely explains the identical ranges on two of the targets.
Eric.
