Back out learning the F70: discovered a very STRANGE audio sound...

Went out for about 4 hours today hunting with the F70. Went back to the junk-filled old homesite I've been working the last couple hunts; I tried the 5" DD coil today for the first time; it was VERY quiet in terms of EMI; I was able to run 99 sens and 9 thresh, though I didn't -- too much small junk so I ran at thresh 0. 4 tones, GB mostly upper 50s. Let me tell you, I have never in my life seen so much junk, and such a VARIETY of junk. I have NO IDEA how so much metal could accumulate in someone's yard! I am still learning the detector; only found 3 zinc pennies -- have NO IDEA where the older coins are, but I'm guessing they are under the JUNK!!

Anyway, I am being BARRAGED with what is almost surely, for the most part, iron falsing. Wish there was something to do to eliminate the falses -- very "sick-sounding" and short/abrupt/staccato high tones amongst the iron that will NOT repeat in four directions (often high tones on a side-to-side sweep, and then iron-tones jumping to mid-tones sweeping 90 degrees, perpendicular). I dug every repeatable, decent tone I could find, and I am amazed at the amount of non-iron junk I dug (along with all the broken iron pieces). NO nails, running 15 disc, but lots of other types of iron. I was fooled several times with VERY solid TIDs, a rock-hard 71-72 that was a dog rabies tag; a couple of very good high 70s, with very little bounce, that turned out to be rolled up/flattened metal "ointment" tubes, and several pretty good tones (to my still-untrained ears) that turned out to be flat, rusty iron, or small, crushed up copper cans/containers of some sort. This place is wearing me out!

I discovered one interesting thing that I have read about -- but experienced today more than any day I've hunted (was it the 5" DD coil?), and that is how the TID "algorithms" and the tone "algorithms" are separate. There were several times where I was getting high tones, and then glancing at the TID and seeing numbers in the teens or 20s. Given the discrepancy between the tones and the TID, I presumed these targets to be junk!

Anyway, here's my question about a very strange audio occurence I am having on occasion. I noticed this the other day, and then several times today. Sometimes, when I hit a jumpy, likely-to-be-junk target, besides hearing the tones (I was using 4-tone), I also hear something else. Very, very, VERY subtle, very quiet -- first time I heard it I thought it was coming from the control box itself, so took off my headphones to listen, but no -- it was IN the heaphones, but "under" the tone sounds. It's a very, very faint but steady hum or buzz. It is NOT a problem with the headphones, or the detector, or anything like that; it IS related to the target, since when I move the coil away from the target, the buzz wanes and then disappears. Swing the coil back over the target, the tones return, but so does that very faint, subtle "buzz" that is "underneath" the tones. I can hit another target that behaves exactly the same way, tone-wise, but the buzz is not there. Only on the occasional target do I hear this accompanying "buzz." Does anyone else know what I'm talking about? Has anyone ever experienced this? I have never heard anyone mention anything like this on any of the forums; I can't narrow down how it relates to the target yet (too much info bombing my brain still to isolate this variable), but instinct and gut tells me this is an "iron" buzz...related to large iron. I need to dig several of these targets, so that I can begin to verify or disprove my gut feeling, but I'm more interested right now if anyone else has experienced this with the F70/F75/T2 units...and if so, if they have been able to glean any clues as to the probable target when this barely-audible "buzz" accompanies the tones.

Thanks,

Steve

........and if the 5" coil is having trouble separating all of these excessive/voluminous, target-rich areas......imagine how that stock 11" coil will do. And how your ears will handle this.
Yes, sounds to me like the good (older) generation coins are deeper..........in the strata below all of the surface/sub-surface junk strata.......and completely masked. Sounds like a very tough site for you to initially cut-your-teeth.

If you are encountering too much high tone micro-chirps........try dropping Grnd Bal (you'll have to do this manually).......by quite a few points.......maybe 20-45 points.........and see if you acquire better results. Sounds like you are hunting Sanford-n-Son's lawn.

I know the sub-lying 'buzz' you refer to. I have experienced this (but only a few times) with F75 and F75 LTD......and at high Sens settings........in extremely trashy areas. Not enough for me to further investigate. It sounds like the primary 'beep' audio response from a target....is riding on top of a threshold buzz carrier. You do not hear this muted buzz carrier.....until you hit a primary target. It is a 'all-or-nothing' condition. Nothing to worry about.

I did not think that dropping the ground balance was possible.
How do you do it?

Tommy C.
(southernexplorer)
Deus - Etrac - GPX 5000

Mr. Dankowski --

I have seen where you talked about dropping ground balance, but the F70 does not have manual ground balance ability. Only way I know of to pull it off is to find a patch of ground (like a gravel driveway or something) that reads lower, balance there, and then return to the higher ground phase areas.

Hunting Sanford and Son's lawn -- now THAT made me LOL! I think you have it pretty much nailed!

As for the buzz, it's interesting that you have heard it too, on occasion, but only in mega-trashy areas and when running high sensitivity. That is exactly the condition I heard it in, obviously; hunted three hours today in a NON trashy park-type situation on a cherry-pick coin hunt, ran at lower (70) sens. (though EMI would have allowed more, this was a modern park with likely no deep old coins). In this hunt, I never heard the "buzz" once. Next time I am on a hunt where I am hearing it, I'll dig all those targets and report.

By the way, this machine was WAAAAY easier to handle in the non trashed location. I was actually able to make some associations as to what a good target sounds like and IDs like!

Steve

At a cleaner site..........your confidence-building learning curve is MUCH faster.

Yes, if only to carry a iron oxide rust flake......so as to trick the detector into a different Grnd Bal setting......since this can only be done in a 'fast-grab' fashion.

Back to a junky spot today -- a park I hit in the past, a very small, very old section of the park, TONS of junk in a small area, near a 100-ish year old tree, where I found a 1913 wheat penny in the past. I ran high sens, looking for deeper stuff, fighting EMI. At one point, I found a repeatable, but jumpy and somewhat faint high tone in a little less junky area, felt maybe I finally had my first deep silver coin, it pinpointed at 10". Nope; after digging halfway to China, it was rusty iron. No good finds of consequence (a couple clad coins), BUT...I got somewhat of an education, because...

...I learned, I think, what the "buzz" sound is. I heard it many times today, only when running high sens (consistent with Mr. D.'s observation), and every one I dug, was a really RUSTY NAIL. The buzz happens in some cases (not by any means all) when you can get a repeatable high-tone iron false. It was always a two-direction false, the other direction gave much lower TID falses amongst the iron hits. The TID when high-falsing, and when the buzz is happening, is almost ALWAYS in the mid to upper 90s, clearly saying "iron;" sometimes you see the "dirt"/Fe3O4, meter jumping up as well. I will test this several more times to be sure, but it appears my "gut feeling" was correct, and if proven so with more experimenting, this is a good "clue" that one is dealing with an iron target. Interesting thing, I think it has to do with the "halo," as the very same nails that gave this "buzz" sound "underneath" the high-tone falsing, would NOT give the buzz (and rarely if ever a high-tone false) when I dug them and laid them on the ground, and then ran the coil over them. Only in the undisturbed ground would I witness the mega-falsing and the "buzz."

Steve



Edited 1 time(s). Last edit at 02/17/2011 08:59AM by steveg.

Interesting synopsis. Will test it if I run into the 'buzz'.

Yes, let me know, Terra.

You know, thinking and pondering this brings me to another thought. I talked about, in my last post, thinking the "buzz" may have something to do with "halo" effect -- all that rust and iron "leaching" into the surrounding soil around these old, highly-corroded nails. The "buzz" sound almost sounds sort of like the "buzz" you hear on a bad phone line, where it's in the background and "underneath" the voice sounds -- only on my detector it is much softer and more subtle, and ONLY occurs when you are in close proximity to a target. Further, the "buzz" sound is "bigger" than the target -- it seems to occupy an area "around" the target (tagets which I now know are at LEAST sometimes, very rusty nails). SO, here is my question. I have been talking here alot about TONS, TONS of iron falsing I'm dealing with. It is WAY more than what I hear others talking about in general. So, I am wondering -- since my soil's primary mineralization is iron (red clay), does this iron in the soil somehow "react" or "interact" with rusting iron, to produce a larger, or "stronger" halo-type effect in some cases, which is then fed back to my detector as "high falsing" (and the "buzz" at times)? Again, the very same nail that causes the "buzz" and the high-falsing will NOT buzz, and VERY RARELY IF AT ALL high-false, once I dig it and place it on the ground. The amount of falsing seems to be SO excessive, that at times it renders my machine almost unusable. But I don't think it's a problem with the machine itself (though it could be), because the machine behaves SO much better away from iron-trashed sites, that it seems to be specifically a rusty iron issue. Could it be the red clay here reacting with the rusty iron (excessive "halos") to exacerbate the problem of the high falsing (and the "buzz" sound is measuring this same issue -- halo around the target really screwing with the detector's transmitted electromagnetic field?)

Just thinking out loud, and wondering if it makes any logical sense...

Steve

Oh, and Mr. D. -- I did try to "artificially" balance my detector lower than the ground balance of the surrounding soil, was able to balance it about 10 points lower than ground phase, but that was not enough to help much if at all. Maybe was not enough lower.

Steve,

I also noticed the "dirt" meter running high on certain high TID readings. Nearly as a rule the resulting target was large iron. I will try to make an effort this weekend to keep track of my reading vs. large iron targets and report back.