Inaccurate depth readings on the F75

Tom and others I have found the depth readings on coins to be way off with my F 75.A 2 inch dime or penny will read 5 inches .Sometimes it's right on though.I have been carrying a small plastic ruller and note book to record information about finds(who does that sound like).The ground is bone dry almost everywhere I have been hunting.You cut a plug and it starts to come apart as powder.Does higher sensitivity and or the dry soil cause this inaccuracy.My pinpointing seems to be spot on most of the time.Thanks Bill

Hey Kick, I'm getting the same, It's off by about 5" in shallow or dry conditions and finding it to be only 2" in moist or deeper conditions (haven't been that mineralized though/65 or so). I also, pump up the F75 a bit. I'm going to try it tomorrow with less sens, and keep it within the 5 and 20 disc (have been going to 4 and finding the audio can aid in trash detection). Have you noticed that pull tabs have been coming in with a silver or high conductive TID on deep targets with the sense pumped up? HH RickyD

MenStick
I haven't had aluminum read as a high tone with the sens turned up,much.If it does the ID numbers bounce around pretty much so I don't dig it,now.If i get a big swing in ID numbers I don't dig it.So far if it pinpoints loud,kind of like the detector is "screaming" it's been trash.It's hard to accurately describe the sound of a coin.When you pinpoint it it has smooth,more mellow sound.I get some deep iron that falses high but usually the ID numbers bounce a little more than a coin.I'm still digging a lot of different sounding tones to learn what this detector is telling me.Thursday I start a stretch of 10 days off.I feel a road trip coming on.Bill

Yep Kick I know what your saying on the coin audio. If it reads deep and it screams at you, more than likely it's trash. When I get a tone that sounds deep and has a high pitch that isn't a squeal I'll investigate. The deeper the target the easier it is to identify. As for the iron falsing it's always shreal and loud, as for the deep coin, it sounds deep (less in db's) and the pitch is smooth and clean sounding but still with a high pitch. Good luck on the road trip, take notes, want to hear what you figured out on the machine. Bring home the bootey!! MeNstick!

If you have the time, read "Beneath The Mask" article in the Article Archives section. It should explain this phenomenon you are encountering. I experience this exact phenomenon every time I go detecting. The T-2, Minelab, F-75 and CZ are very accurate ... regarding their depth ID abilities. You are encountering silent masking. I believe I thoroughly covered this exact topic in previous threads below. Silent masking is MUCH more prevalent than masking. What makes it worse... is that we would NEVER know it. We would NEVER know it is happening.... because IT IS SILENT! Yes.... once again..... HOW DO YOU KNOW WHAT YOU ARE MISSING,,,IF YOU DON'T KNOW IT EVEN EXISTS! It is not uncommon for me to carry 10 lb mono fishing line into the field.... so as to rapidly scrape 1/16" dirt increments off of the bottom of a excavated plug.... so as to find the silent masking culprit. ... Usually looks like a blood spot in the soil ( red/brown iron oxide soil stain ).
Recently, FINALLY...... I had this experience happen to me with the F-75 AND the CZ. (( Seems like this incorrect depth ID phenomenon is more prevalent with F-75 vs. CZ )). Found a bouncing signal ID of Square-Tab/Zinc reading at 9" with the F-75. The CZ verified and validated this same exact reading. I dug a 6" x 6" x 6" cube of dirt-plug and flipped it up-side-down.... several inches away from the hole. Sweeping the detector over the hole... I was certain the target would still be in the hole.... and needing approx 3" more of soil excavated. Nope. The target was not in the hole. Sweeping the coil over the bottom of the excavated plug... yep, it was there... and 3" deep. Flipping the plug back over to grass-side-up,,,,, the target was now depth reading at 9" deep. And again.... flipping the plug back to up-side-down config..... and carefully digging/finding the target nearly exactly in the middle of the plug (a somewhat corroded 2002 Zn penny). BEFORE 'unsticking' the exposed penny out/off of the plug..... I left it in place and flipped the 3" deep plug BACK over to the grass-side-up position..... and ....... sure enough.... the penny is reading 9" deep. ... ,,,,, Flipping the plug up-side-down again...I then removed the penny and used the mono fishing line to rapidly shave 1/16" increments off of the plug to.... sure enough,,,,, find a pair of blood spots in the soil. Just enough to ALMOST completely SILENTLY mask the 3" deep Zn penny,,,,, and; hence, give a depth ID of 9". WELCOME TO THE REAL WORLD! One of the two blood spots still had a VERY small piece of nearly disintegrated unidentifiable rust/iron. This target sounded a bit audibly 'ratty'...... and pin-pointed about 1/2" off center... but I still decided to recover it. To my surprise....Turned out to be a coin. Only the 'cherry-picking'..... no masking, no silent masking..... coins sound perfect.... and pin-point perfect. HARDLY the real world!

Tom

There is more decaying iron flakes in my soil than I every imagined.Thanks.I never thought of silent masking.I find"blood spots'in plugs and plug sidewalls all the time.

Most folks are completely unaware of this.

NASA TOM...!!!... Great info, Me living in the red clay state this is info for the Wise...I like Kickback Find the brown/red rusted blood stains with almost every Dig..And often find the Deteriated small metal flakes you mentioned everywhere..more so when Relic hunting..Thanks james

I remember hunting with (about the 4th or 5th generation proto) T-2 at a particular site where I knew the unit would shine...... but the T-2 was the most unstable unit I had ever used....and could find nothing. Severe reaction to the ground. Coil was acting like the shield paint had failed. Was very upset with this particular proto..... as I thought most bugs had been already worked out by then. Frustrated and distraught. BUT....... for some triggered reason,,,,,,, I clearly recall digging approx 2 cu. ft. of loamy/sandy soil out of the ground...... and decided to take a magnet (twice the size of my fist).... and plunged it into the middle----pile of dirt so as to (hopefully) remove a couple of nails,,,making this soil more detectable. To my TOTAL surprise...... as I pulled the magnet from the soil.... I did not find any nails. What I found was....... my ENTIRE arm,,,,,, almost up to my elbow..... was COVERED in a spherical ball of rust flakes; nearly up to my elbow. The spherical ball was about the size of a basketball. Somewhat unknowingly..... I now had the answer as to why the T-2 responded the way it did. It is VERY sensitive to tiny targets..... with a extremely rapid microprocessor wanting to report every little rust flake. The Explorer just simply 'shut down'...... and could detect nothing in this particular area. CZ...... same thing. At least the T-2 was trying to seperate the targets.... as it tried to report everything it possibly could..... within it's design capabilities. It was audibly fatiguing to me... as I could not mentally handle so many rapid audio 'blips'. Using the other detectors..... I would have never known that these crippling conditions existed.... to this order-of-magnitude. The T-2 was experiencing a severe case of masking; the other units were experiencing (to a much greater extent) a severe case of SILENT masking.

Tom I found a old ranch headquarters.The floors and foundation walls were field stone,no mortar.It had several bunkhouses and a large main house.I found out this was the first ranch in this country.The ground is so full of "bloodstains"and visible tiny rust flakes neither my CZ or F 75 can find a non ferrous target.It's a shame as this is a pre 1900's site.I never thought about silent masking.Until I asked the question on your forum.Thanks again.Bill

Bill,

You would be SHOCKED to know how many non-ferrous targets are in that location! Fact of the matter is; that's the real world! If only to go just one more generation ahead..... detector wise.

Tom

"If only to go just one more generation ahead..... detector wise."



It's right here: [www.xpmetaldetectors.com]

Interesting.

"Iron volume" of the XP Goldmaxx, makes PERFECT sense. It's amazing that none of the 5-10 U.S. manufacturers have thought of it. I haven't dealt with a bunch of higher end units, but the one thing I like about the Ace240 (vs. my F4), is that the indicator still shows iron even though you're not hearing anything.

Regton's tests (which includes the a test of the Goldmaxx Pro) do show that you could hunt an area and miss dozens of targets should they be aligned in certain ways with iron (or if the soil is iron rich). From his tests, it's an easy conclusion that you'd miss a significant amount less with an XP.

Now who in the heck is going to convince Fisher to add a volume selector to the descim circuit or at least talk XP into selling their detectors in the U.S.!!!?? Someone!?



Edited 3 time(s). Last edit at 07/11/2008 03:06AM by Shambler.

RE:Now who in the heck is going to convince Fisher to add a volume selector to the descim circuit or at least talk XP into selling their detectors in the U.S.!!!?? Someone!?

Maybe "Mr. Bill" can figure this one out so Fisher ownwers can take a chance on their warranty like White's detector owners can...kinda funny but, if he could (or anyone could) modify the F-75 to the specks that would do what is written in above post, I believe many would pay some bucks for that.
just a thought.

I am one of whom is VERY skeptical..... and would have to run head-to-head tests to truly see if there is any merit; subsequently.... praise ---- exists. I can not imagine anyone else has come out with a unit that has the clock-speed with that of the F75/T2 microprocessor. And to press forth.....this order-of-magnitude... coupled with the extremely tight DD footprint of these biaxial coils. Now..... the principles of EM, iron response, dirt response...... with the basic principle-of-operation of metal detectors shall have the same handicaps. I know that I have said this many times before...in previous posts.....and in MUCH greater detail....,,,,,,,...... but worthy of mentioning again. That being:

You can find the nominal average ID reading of the nails in your chosen specific area that you choose to hunt. THEN...... adjust your iron Disc accordingly, so as to JUST BARELY Disc out the bulk of the common iron. NOW...... any nail that is JUST BARELY Disc'd out...that has a Non-Ferrous target in extreme close proximity...will (now) MOST PROBABLY break through the Disc setting... and give you a audible response.

Not sure how this 'other brand' detector performs in such a fashion.

Tom

Booooooo I'm not sure quotes around 'other brand' is fair.

I have an F4 and an ACE250. In my day dreams I have an F75 That being said, if I could get my hands on the XP Goldmaxx Power, I would sell something (anything!) and get it now. I'm that impressed with the SIMPLE idea of iron volume (and wireless headphones, and USB connectivity... see 'other brand' Adonis). My F4 finds things that the ACE misses, but I'm certain based on test bed results of iron masking, that (statistically), I've missed things.

I recently went out using my F4, my son using his Ace250, and my Dad using his Coinmaster 3900d pro that he purchased in 1981. We all had the same level of success (and failure). The 3900 can discriminate and pinpoint with a mid-level priced machine from over 20 years ago! AND it was only 4 ounces heavier than the F4!! I can't help but feel the industry is playing games with the marketing of bells and whistles that in reality change nothing (and sometimes make things MORE complicated with little benefit).

If you look through the UK forums and apparently a Belgian one mentioned here: [www.treasurequestxlt.com], you can see that people graduate to the XP Goldmaxx's. The U.S. high end detectors are cheaper, but they go with the XP's. I think Fisher and the other US manu's should pay attention to that. It would seem to mean that if the French company decided to market it here, it would put a serious dent in the hobby sales of the 'U.S. Manufactures' (I had to do it ... hehe). Sometimes market pressure gets things done... that's the intent of my post. Not to argue about the technical facets of the F75, but to say there are some other things that Fisher could do that would make the machines even better.

My question for Tom is if you're at a site that's had human activity for 200 years... where barns and buildings have been built and torn down (trading post, house, and school from 1805 in Indiana) I don't see a way even with the superior F75 to just descim a certain type of iron. BUT you'd have to use a bulldozer to remove all of the iron on this property in order to find things that are surely hidden by it. You're kind of stuck descriminating all Iron. So, with an iron signal that is very faint (iron volume) and a very fast recovery speed, you'd know where you should be spending more time and trying different angles so as to lessen your chances of missing something valuable.


Here's Regton's written field test:
[www.metaldetectorshop.co.uk]

CAUTION: apparently it does NOT protect you from sheep:
[youtube.com]



Edited 1 time(s). Last edit at 07/14/2008 02:57AM by Shambler.

Interesting field report. While I applaud the XP GoldMaxx' ability to having the ability of reducing human fatigue factor..... by virtue of having a volume control for the 'iron only' portion of audio reports; By virtue of reducing the volume on iron ... does not constitute enhancement of "iron see-thru" ability. Now,,,,, that being said,,,,, the faster clock speed of the microprocessor should greatly enhance the XP's (or any detector) ability to separate adjacent targets to a greater extent.

There still remains a popular misconception amongst the detecting community; that being the false misconception of = "If I Discrim Iron, I will not hear it; therefore, I will be able to see thru the iron and hear only the good targets beneath the iron". NOT TRUE!

I'm the type of person of whom requires Head-to-Head .... REAL WORLD scenario testing..... no handicaps given,,,,,...... in order to make accurate/concise judgement calls; whilst all along,,,,, understanding that the resultant may NOT be a 100% - to - 0% final tally. It's usually a mixed bag,,,,, with one unit having/presenting a greater 'overall' rating/report.

And to answer your other 'loaded with iron & nails' question;
The T-2/F-75 picks good targets out of iron infested dirt the best... as compared to other units; HOWEVER, they are still fully handicapped to the effects of masking and silent-masking. There is no magic widget for this yet....... and probably will not be..... unless we make the paradigm shift away from the utilization of electromagnetics as a detection medium. --- Blinded we are!

Tom