settings look fine, signals loud and clear, huge signal .... So why .....

[JimH]

So why when I get the best signal EVER, it ends up being a bottle cap ?? Now I understand that we have to take the good with the bad, but every time I had this combination, it was always bottle caps !!!! I even consulted with others on the beach that were more experienced, but the signal came back as high 90's and silver!, but it was anything else than silver. Using Garrett AT PRO, using moderate sensitive, eliminating junk sounds with audio settings, discrimination levels are at moderate levels - so why does junk look exactly like silver ?

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[Charlie P. (NY)]

It's all based on conductivity. Don't know the AT Pro, but you may be able to select a mode that makes the bottle caps less attractive. Also, lifting the coil while sweeping can help as bottle caps aren't as sweet as you back off a bit when raising the coil.

[JimH]

Charlie.... Thanks for the feedback. You'd think with all of the discrimination options available today, beer caps could be easily ignored, like the pop tops. Now it seems like I paid good money to invest in a device, with all of its technological advancement, that can't really do anything more than the detectors of the 60's & 70's. So, does the conductivity of a beer bottle cap also equal that of high grade silver (>95)?

[JimH]

It seems Socrates had it right all the time. He said "The more I learn, the less I know". I guess this can apply in any learning situation. In my haste to complain about my high level of expectations, I should have done the right thing, and researched my own issue. You were absolutely spot on when you mentioned conductivity. I had no idea that our metal detectors were searching in such a fixed and focused area, when it comes to precious metal. There is a very good wiki that provides the technical aspects of this ...... List of thermal conductivities - Wikipedia, the free encyclopedia.

[Jim in Idaho]

That's thermal conductivity, not electrical. Our detectors work on electrical conductivity. One of the answers to your bottlecap question has to do with shape as well as conduction. In my experience round objects tend to act more like the good stuff than irregular shapes. That includes pull tabs, bottlecaps, and a host of other junk we seem to find. I guess the discrimination circuits have trouble separating out the round stuff.
Jim

[stevemc]

Plus bottle caps are plated with tin, to keep them from corroding. They ring off on about every type of detector. Some you can tell what it is, but you might be eliminataing something good.

[Stormrider1951]

What everyone is telling you is true. Detectors read conductivity. They keep making them better and better but no one has yet defeated that one failing. A bottle cap is going to show up as a good target. Notch discriminate one out and the next one, with a slightly different conductivity, will still cause your machine to sound off. Same thing for pulltabs. What I've seen over the years is that as detectors get more sophisticated we dig less trash but we also find fewer rings and other small pieces of jewelry. That's because those desirable items are in the same conductivity range as pulltabs and caps. Same goes for nickles. I base my success in hunting on how many nickles I come home with. It may be dumb but I just love pulling a nickle out of the ground. Doing so tells me that I'm not missing things I'd like to find. Just my preference and others may not agree.

Storm

[russ]

If in doubt mate dig em out, especially on the beach, its easy digging and youll get all the good stuff as well as the bottle tops. good luck.

[Ace350]

I hunt in Pro mode Zero with Iron Disc set at 38 and when I get a hard signal like that, I turn on Iron Audio and listen carefully and watch the VDI numbers.
Usually if it's a bottlecap you hear a low iron tone kinda like a grunt or you get a slight grunt then the high tone then a grunt again. Sometimes it doesn't ding on both swing directions of the coil.
As mentioned in the above posts, the VDI usually jumps around more drastically and a coin is usually a steady number or it bounces only a 1 or 2 number difference.

To learn to tell the difference start collecting those bottlecaps you dig up. Different caps sometimes give different readings so it's good to have a few different kinds. Take them out in your back yard and put them in the grass and test them and listen to the sounds with iron audio on and off. With it off it sounds like a coin. Look at the VDI numbers also they will be jumping around. Bring some nickels and quaters and try the above with them and listen to the sounds and watch the VDI numbers.

You have to learn your machine before it will perform to it's full potential.
Good luck and happy hunting

[cti4sw]

It's all based on conductivity. Don't know the AT Pro, but you may be able to select a mode that makes the bottle caps less attractive. Also, lifting the coil while sweeping can help as bottle caps aren't as sweet as you back off a bit when raising the coil.

I have also noticed this with my BH Tracker IV. Close to the dirt, the trash has a strong signal unless you come at it from different heights and angles. Of course, I usually dig it up anyway lol...

[Frankn]

OK here it is, I use to think the detectors knew what metal was there, but after experimenting and reading up on my electronics, here's the real story.
Your detector does not know what metal is there! It sends out a signal, call it 100%. It receives a lesser return signal and feeds it to the signal processor. The processor is calabrated in coin size returns. The strength of the return signal governes what is shown on the meter, or the sound. For example, The return signal strength from a quater will display quater and show a ID # in the silver range. So your bottle cap is returning the same signal strength as a coin of slightly smaller size. We have gotten to think there is magic in that box, but it's just a programed guess in there.

[smcdmc]

OK here it is, I use to think the detectors knew what metal was there, but after experimenting and reading up on my electronics, here's the real story.
Your detector does not know what metal is there! It sends out a signal, call it 100%. It receives a lesser return signal and feeds it to the signal processor. The processor is calabrated in coin size returns. The strength of the return signal governes what is shown on the meter, or the sound. For example, The return signal strength from a quater will display quater and show a ID # in the silver range. So your bottle cap is returning the same signal strength as a coin of slightly smaller size. We have gotten to think there is magic in that box, but it's just a programed guess in there.

But that signal strength will vary depending on what kind of metal it is made of.

[Jim in Idaho]

OK here it is, I use to think the detectors knew what metal was there, but after experimenting and reading up on my electronics, here's the real story.
Your detector does not know what metal is there! It sends out a signal, call it 100%. It receives a lesser return signal and feeds it to the signal processor. The processor is calabrated in coin size returns. The strength of the return signal governes what is shown on the meter, or the sound. For example, The return signal strength from a quater will display quater and show a ID # in the silver range. So your bottle cap is returning the same signal strength as a coin of slightly smaller size. We have gotten to think there is magic in that box, but it's just a programed guess in there.

It isn't just strength of the signal. The signal is returned out of phase with the transmitted signal. Since different metals re-transmit the signal at different speeds, the amount of phase difference changes with the metal type. That is how a modern detector discriminates. The detector compares the transmitted signal to the received signal and determines the metal type. It isn't perfect obviously, but does work to some extent. The problem is the size of object affects the phase of the returned signal, and can fool the discrimination circuitry...thus it ain't perfect.
Jim

[Lakemonster]

Put that thing in pro mode... grab a bottle cap and a quarter. Put them 2 foot apart and listen to both of them.... the bottlecap will make a "warble" like sound.

[kayden]

Put that thing in pro mode... grab a bottle cap and a quarter. Put them 2 foot apart and listen to both of them.... the bottlecap will make a "warble" like sound.

This !