Hot rocks and VFL

[Henrikras]

Hi all.
Any who can explain why stones like a hand i size are giving signals at some VFL detectors. Turn on and go detectors I got and tryed, dosn't do that. The way I handle this, is to GB with a Stone like some are using a ferrite piece to find GB.
But in all situations doing that, my GB is way out of balance.. Then I have to decide, either hotrock (stones) signals and good GB, or the reverse. None Minelab VLF I tested did this, XP didn't either, My Teroso Vanquero allso not, but my Vista Gold and my Blisstool (funny both from Bulgaria) are doing this. Last my Nokta Velox one, only Very small problem with that, but there a little. If I take my XP Deus which is running nicely in our soil with GB 87-88 and try GB 75-80, same result that some stones makes some alike signals.
It must Be some GB issue and how the Detector is made, but do any got a good idea If I could try to avoid this !
Regards to you all.
Henrik

[dfbowers]

Hmm. I know that some detectors with preset GB are adjusted way too positive, but it must be because they need to function properly over a very wide range of ground. My Cibola and X5 are set up completely different when it comes to preset GB.. Also, I come across at least 3 types of hot rocks, at least here in the eastern U.S.
The most common ones I come across look like coal. One of my rock hound buddies gave me the technical term for it but I cannot remember at the moment.
I can just bump the Disc control a bit and eliminate them but there is a fine line between thin brass and these.
Another type I encounter gives a negative response, almost like a magnet. I dig them out of curiosity.
The third type is like pottery or bricks.. I don't see those too often.

[kt315]

simple rule is more sensitive detectors give the signal on hot rocks, less sensitive do not give the signal. that is why sure that you write about turn and go detectors, they are not so sensitive. may be strange but GT/Elite has not GB tuning like a pot. I may only guess that is released as automatic algorithm in the micro.

[Henrikras]

Thanks... It must Be that some stones got Heavy mineralization, and its different from country to country, which type and If we got few or many of them. We got many I would say. They are not giving a clear signal, more like a long howling Sound / tone.
I was just naive and thought that Maybee it could Be reduced in the design / adjusted in the coil work by phase chance.
Henrik.

[muddy fingers]

Hi all, dfbowers you say that you have three different types of "hotrocks" in the eastern U.S. and one of these looks like coal. I wonder if that is what is called "coke" in the UK which is indeed burnt coal. I only recently found out that you get rid of it with the Disc control on a detector whereas for "hotrocks" you get rid of them with the GB control. They are two entirely different materials as "hotrocks" are defined as "dense, magnetic, often ironstone, different in density to surrounding stones in the ground" (Quote from Nigel at Regtons U.K.) I have had the same experience as Henrikras as I didn't even know what a hotrock was until I got a Blisstool! I was able to GB them out (Blisstool) but as Henrikras says, that may make the GB wrong for the general area with a resultant loss of depth- I'm not sure. My previous detectors, 1980-90s Garretts and Tesoros weren't the switch on and go type-the Tesoros had ten turn potiometers for GB but I never found a hotrock with either of those brands. I think they must have been set up with a fairly positive GB to start with and the pot just increased it all the more. I know the Garrett ADS was advertised as being for use in "black sand". Neither types could be used very successfully down the beach in the wet sand which requires a lot of negative GB I think.