Less gnd noise at early times...

[Kev]

Greetings,
I was recently searching a place with some of the worst ground noise I've ever come across. It took lots of determination to remain focused on the threshold, but it paid off in the end. A nice little 4 gram specie came to light. It gives an SG figure of 75% gold. Some of the rust has been removed with HCL acid, but I didn't want it all to fall apart so stopped at this point.

The dream is to find the mullocky leader that gave birth to it, still I suspect that it

 

[Eric Foster]

Hi Kev,

Congratulations on the find, and the nice picture you have posted. The Goldquest with a DD coil looks to have some good potential as a nugget detector in all but the most severe mineralisation. Certainly at 5uS delay, its sensitivity is such that nuggets that would be invisible to other PI

 

[Kev]

Thanks Eric,
It was a surprising find to say the least, when I dug down to get it (about 5 to 6 inches) and was passing the soil over the coil I expected to see the glint of yellow, but was confused when this grubby little rock gave a response, but then I noticed the weight of it relative to its size. A bit of spit and polish later had my heart racing, since I was at the bottom of the slope and 10 minutes into my detecting...I had visions of pocket loads of ore....didn't find another scap all day LOL.

I was using a 60us pulse. I plan to try a shorter pulse soon, so will let you know if it helps. 60us is still relatively short in comparison to many machines. I compiled a new program last night and will be heading back there at the end of the month. I'm using an 8 pin micro to clock the 4017 and I/O is limited so I only have a small number of pulse widths programmed in ROM, and I've tended to use 60 to 80us. I can though adjust the delay from 3 to 12us in 800ns increments.

In an air test the specimen range varies by about a third between 10 and 5us, so shorter delays sure do help with porous targets, and as it appears with ground noise.

Image shows the controller board that piggybacks the 4017. It also has an extra sampling channel.

Cheers
Kev.

 

[Kev]

Hi,
Reg has pointed out to me that I have omitted one factor that may have contributed to what I

 

[Kev]

Hi,
I have extra DC gain, so if you try this, the trimmer may need to be a half Meg Ohm, or alternatively use dual diodes in parallel i.e.

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Cheers
Kev.