Coil magnetic field question

[multieagle]

This question concerns the coil detection pattern above and below the coil. I was bench testing a VLF coil today, using about 1/2 gram of flake gold (several pieces) secured between scotch tape. I attempted to detect the sample beneath the coil and could manage only very scratchy reaction, and that with the sample almost pressed against the coil. By accident, I passed the sample over the top of the coil and was surprised by a very sold hit. After several passes, up to around 5 inches, I continued to have this reaction. I again tried below the coil, with no reaction.

Thinking I had a defective coil, I tried other items, gold chain, gold and silver rings, coins, pull-tab, etc. etc. and all gave good signals within the expected range.

So for the question. In a VLF coil, is it possible to have two difference frequencies operating at the same time? Unless there is a scientific reason the gold was detected above and not below, it would appear a higher frequency is being generated above the coil. Does this make sense?

Confused.

[Davor]

Could you make a photo of your coil?

[Skippy]

"Does this make sense?" Not in the slightest. The shielding of your coil could be different above the coil and below, eg. graphite-painted below, nothing above. That might be one explanation. Are you holding the test targets in your hand? If so, it's possibly your hand that's being picked up. Try blu-tacking the target to a plastic ruler or something similar, then wave it over the coil, so your hand is kept away.

[multieagle]

I retested today and was unable to reproduce the effect.

The best I could do was around 2". Strange. My test platform is within an urban setting, on a plastic yard table with no metal parts. The coil and machine are about 4 feet from the ground. There are no overhead transmission wires, and the Bliss was very quiet. The strange effect I had yesterday was that I was able to detect ABOVE the coil to around 5 inches. Whilst under the coil, the detecting range was within 1 inch.

Today everything evened out and the detecting range was about 2" on either side of the coil.

Obviously there was a variable yesterday which I missed.