Strong signal cancelling machine

[DannyB1954]

I originally posted in the wrong forum, so my apologies to admin.
I was wondering if a detector could be made to ignore strong signals. If you are searching for deep old coins or relics, a strong shallow signal is distracting.

I am thinking of a variable resistor or digital control that can be adjusted for clipping signal strengths over what it is set for. I don't really know what the signal strengths are, but say a pop top at 1 inch reflects 50 dan units, (named after me), and a coin at 6" reflects 5. the selector can be set so that anything over 40 dan units will be ignored. This would be adjusted as per the site's trash content. It would seem an easy task for a microprocessor. Most can figure out how deep something is, Just instruct to ignore anything less than what you set the dial for. Anything strong enough to be new is to be ignored. The dial could be calibrated by depth or by signal strength.

The purpose of this would be to pass over clad coins and aluminum trash. If minimum wage is $7 an hour, you would have to dig up 28 quarters a hour to meet that. I can see where this would benefit relic hunters as well. I don't want the pull tab lost a year ago, I want the coin or ring lost many years ago. What you would lose in lost targets you would more than make up for in productive digs.

 

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[Tom_in_CA]

Danny, yes this has been thought of as far back as the 1980s. Easy electronic filtering, as you've surmised. It was called "blanking" or "surface blanking". But the devil was in the details (and still is).: Anytime you are on the fringes of a loud signal (ie.: not quite "centered") , your machine will get that fringe/snippet , and correctly temporarily interpret that as an accept. Yoohoo! so you go to isolate and center that "target", and guess what ? It disappears. Or conversely, you go to isolate and center over a deeper one (smunching the coil, getting exact centering, etc...), and now it rises that (on isolated bounces too, which is extremely frustrating) and , well, you get the picture.

And you would end up doing what those guys back then did: ditching such electronic "computer-think-for-you" methods, and just using your ears to reject surface clad (a much better computer in this case).

also as an interesting aside: Some people back then thought this "surface blanking" was a way to magically see through surface trash, to eliminate masking. Obviously it was nothing of the sort. It was just intensity measuring (with all its downfalls). An item under a surface trash was still masked. Eg.: if you put a dime under a manhole cover, and "reject the top 4", you will NOT get the dime underneath the manhole cover. Doh!

 

[DannyB1954]

Thanks for the awakening. I thought it would be so simple.

 

[cudamark]

Yup, too many different kinds of targets at varying depths to have an accurate surface blanking feature. a deep large target will many times read the same as a small shallow target. Using your ears and the depth gauge on the machine is a better method.