Jp’s Audio Visual Gold Thread

[flakmagnet]

4 hours ago, Jonathan Porter said:

incrementally without realising it you minutely adjust and refine the sweep speed, the range of motion (two very different things), centering of the coil relative to the potential target and finally gradually changing the height of the coil relative to the target and bingo the signal pops out of the ether.

I agree, that tracks closely with what I have experienced. But your explanation is much more concise. 

[Redz]

Hi JP,

I appreciated your discussion of indicators you look for. I was hoping you would continue that thread

[Jin]

On 4/1/2020 at 6:50 AM, Jonathan Porter said:

What’s actually happening, from a scientific point of view, is as you sweep you are hearing ‘something’, that something is enough for you to continue passing the coil over the zone trying to get the target signal to manifest, incrementally without realising it you minutely adjust and refine the sweep speed, the range of motion (two very different things), centering of the coil relative to the potential target and finally gradually changing the height of the coil relative to the target and bingo the signal pops out of the ether. This sub-conscience incremental adjustment is a big part of the whole gamut of visual, tactile and audio sensory input associated with metal detecting.

Sometimes the sweet spot is so tight that you ‘pop’ the target only every so often as you pass the coil in through the epicentre of the target zone, this happens a lot in saturable ground as the target signal can get blended in with saturation noise so you only have a few millimetres to play with between the saturation signal affecting the threshold and loudest target signal point, this is one of the reasons why I am not a fan of coils that saturate badly!!

A trick to try, when the saturation signal is messing with proximity to ground, is to scrape a wide area over the range of motion target zone because saturable magnetic particles tend to concentrate in the surface soils, scraping them away can give you a few millimetres more room to play with allowing the coil to almost couple to the ground. This method is effective on small shallow targets especially but also beneficial on the larger deep gold that does not increase very much in signal, in fact the lack of signal increase when I clear the saturable materials always brings a smile to my dial because deeper often means bigger.

JP

Thats an interesting explination. So thanks for sharing that. I always thought it was the ground balance at work. 3 or 4 swings usually gets rid of ground noise so i presumed that as you swing back and forth over a target it was removing some of the competing ground noise allowing the gold signal to stand out.  

[mn90403]

This explanation as I read it again now would explain 'raking' a patch as many have been done in the past.  Many tiny nuggets would be masked with the surface materials.  Sometimes we would rake them to smooth them and get the coil closer to the ground but now it seems that the surface saturation was being raked away with it also.  This raking would go on to the edge of the patch.

This has always been one of my clues as well as previous dig holes.  Some of these rake piles are 20-30 years old now.  They are quite different from oldtimer workings and drywashings.

[vanursepaul]

Thats a good observation Mitch, you are thinking and using the new knowledge to apply it in the field...

I would have missed that angle.

But it is logical.

 

[Jonathan Porter]

8 hours ago, mn90403 said:

This explanation as I read it again now would explain 'raking' a patch as many have been done in the past.  Many tiny nuggets would be masked with the surface materials.  Sometimes we would rake them to smooth them and get the coil closer to the ground but now it seems that the surface saturation was being raked away with it also.  This raking would go on to the edge of the patch.

This has always been one of my clues as well as previous dig holes.  Some of these rake piles are 20-30 years old now.  They are quite different from oldtimer workings and drywashings.

The VLF guys were trying to achieve two things, one was by removing larger surface stones they got the coil closer to the ground, with a VLF that is vitally important for depth because they suffer terribly from ground noise (due to the Constant Wave sampling during Tx) the other advantage was the bulk of hot rocks are the surface pebbles which become altered over time due to being on the surface, they tend to kill VLF depth because of their highly magnetic nature. 

These same surface pebble accumulations are what add to saturation signals in modern Pulse and ZVT type detectors. This is why PI machines are so good for prospecting they have incredible sensitivity to small gold using larger coils and cope with the ground signal incredibly effectively allowing large tracts of land to be covered in a very short time frame. In the days of Normal timings those surface pebbles were still very problematic especially the MPS dual-voltage units (GP series), thankfully the Smooth/difficult class of timings made major inroads into that problem.

JP

Pic of an old VLF patch I worked with SteveH and ChrisR some years back. If you look carefully where Chris is on the right you can see where all the big stones have been raked up into circular rows. We had a blast working this little spot with Gold Bugs.

[mn90403]

Do you still have any of your Arizona pictures?

[RedDirtDigger]

Some of my most memorable days have been in the remote east pilbara in wa when i have walked onto really old raked areas  (maybe with a dozen old 9volt batteries laying around). Gold everywhere deeper down and downslope some bigger slugs that the vlf machines from that first detector rush could not hope to hear.

Tip, When you find more then a few old batteries laying around on the goldfields have a good look around....and pick up batteries.

[Jonathan Porter]

Did a small video yesterday of the effects of Audio Smoothing on an un-dug 1.5 gram target. This signal was a pretty obvious sound and was responding well in all Audio Smoothing modes, on edge of detection signals the reduction in audio information would be more profound.

When listening to the file listen to the threshold volume as a guide to the effect Audio Smoothing has on the audio of the detector. Audio Smoothing also reduces the ‘Lead IN’ and ‘Tail OUT’ as the target has to reach a certain point to break through the filter which makes the target signal sound steppy, basically coming from nothing into the point where the target breaks through the restriction. Although it kind of sounds less cluttered and nicer to listen to (Decoupled from reality and less fatiguing) the risk is losing information on the edge of detection responses that don’t even pull you up. This signal was initially extremely faint because of leaf litter, but bounced pretty rapidly once I scraped back the loose surface layer. 

Pic of the 1.5 gram piece and the haul I got during yesterday’s session

 

 

I’d like to dedicate this video to the memory of my good friend Fred Mason.