F-75 IRON Discrimination

[HumblePie]

Hello Everyone,

I've been using my Goldstinger for general prospecting in the All-Metal Mode for some twenty years, and dug everything up until about five years ago. The areas I search are inundated with large (and small) iron...particularly iron bars approx. 6 inches long and 1+1/2 inches in diameter. At depth and depending on orientation, these bars read similar to good nickel and silver ores. You may have a pretty good idea that it's iron, but you can't be sure...so you dig. The Goldstinger cannot discriminate these bars (and was never designed to either) without eliminating everything else, so about 5 years ago, I started using the iron discrimination on my Spectrum XLT. When you can get a good solid signal (frequently requiring some digging to get closer), the XLT will give you a reliable iron indication; even if the audio sounds reasonably good and "diggable", the visual signagraph is more accurate and will reliably build bars either scattered right across, or, at least on the negative left side of the graph. (I've proven this reliability many times to myself, while in the same customized Relic Mode, a small low grade piece will read beautifully with a VDI about 3 or 4, so please, lets not debate this here.) This saves me a lot of unnecessary digging, and has made the past five years far more productive.

I do not use the XLT for prospecting (for reasons I don't want to discuss here, but it's just not suitable for me), but I do have to carry it along as well as my other detector and equipment to check suspect iron bars...which is the reason I've been looking at updating my almost 20 years old equipment. I'd like to find a detector that's lightweight, metered in all metal (as well as the discriminate) circuit, operate close to say 15 kHz frequency, and is able to give some indication or clue.. when over these iron bars.

Will the F-75 perform this task? Would some of you mind doing a quick bench (air) test on similar size rusty iron, both with iron discrimination, and without it. Maybe check in the bottlecap mode as well for comparison. Another question...which is more reliable...the visual, or the iron tone? Your help is very much appreciated, so please let us know your results...thankyou...Jim. PS...pls feel free to PM me.

 

[vlad]

The F-75 is great on identifying the iron, and pulling coins out of iron infested areas. I've been out 12 times with the newest version of the F-75 and so far its about 600 coins vs 1 b.c. On the 1 cap, it was well after dark and I was in a hurry so when I got a high tone in delta pitch mode I just dug it. After seeing it was a cap I used the recommended method of sweeping to past the heel of the loop, and it gave an iron grunt [it also does the same if you go past the outer edge of the side of the loop.] Iron nails are non existent as a problem. [I hunt in disc mode, disc set at between 5 and 8, while Bill Ladd recommends the all metal mode, but I'm in town looking for coins not relic hunting-YET.]
If you want the best iron killer on the market which will work with both VLF & P.I.s, do a google search for the FERROUS HOUND, which identifies iron to depth-this is an independent device that you can attach to any detector that you have.

 

[Charlie P. (NY)]

Deja v

 

[liquid1]

I just did a good relic hunt in a big iron infested field early 1900 Iron which is crusted and got some major Hi tone falsing in disc from
0 to 25.. in all the modes DE<JE<PF.I have since learned the old Iron in my very mineralized soil , (.3) can cause falseing ..if its in the ground..pull it up and lay it on the ground and the F75 will not pick it up when disc out..I have learned that I need to pay more attention to the confedence meter over iron it will go up more..I am 3 months old to the F75 and still learning..the machine is very good at giving you information..I noticed that when I would see 80,90 on the vdi and swept the coil tilted just a tic I would get a faint null burp sound..But I am relic hunting so I dig everything just hoping for a coin somewhere around the Iron or old wagon parts ..A good GB in Bad mineral ground is the ticket to depth and good seperation according to nasa tom..With every hunt theres something new I notice the F75 is either showing me or telling me ..Its an awesome machine...james

 

[HumblePie]

Charlie..thanks and see my reply elsewhere...Jim.

 

[HumblePie]

Thanks Vlad...I was wondering if you could check a bottlecap in bottlecap mode, 2F tone, with iron disc set to 0, then 8, then 15 and let me know how it responded both visually (what did the meter settle on), as well as the audio (ie.broken signal, grunt..what?). Thanks...Jim.

 

[HumblePie]

Thanks for that good info James. Here's a question or three: When you got the higher false readings on the buried iron, did you suspect it was iron before digging? Also, do you recall if you looked at your confidence meter while checking the signal, and what it indicated? Finally, how big was the iron? Thanks...Jim.

 

[liquid1]

Hey jim..When I first hit a few targets..I was jumping outa my boots..VDI read 80 on some targets and 90 on some kinda jittery not locking good.. at first I think i was so excited i didn't here a faint grunt..the IIron was a good 5" down and No I never noticed the confidence meter..A real rookie move..I have since this hunt learned a few things to look and listen for..
I was digging every tone from low to high But the Hi tones got my attention especially the smaller square nails 6" deep or deeper..I included a few pic so you can see what i was up against..this is a 5 hour hunt 1.5 acre area.loots of digging.ground is hard as brick batts...and every piece is a different hole dug..after a few 10 or so targets with discrim 15 or more I began noticing a faint burp tone when I swept the coil at a angle..Its Iron thats been in the ground since the early 1900..I am going back to the same location soon and will be more coin hunting so I will pay more attention to the conf and feo meters..the place is highly infested with old IRON.. the feo meter read .2,.3...and fast grab GB 70 so I manual down to 50GB nasa tom told me to try 30 or even 20 the ground is highly mineralized..heres a few pic..old wagon parts and farm parts.I could pull up the nails and lay them on top of the ground and the unit would not give tone..this is an extreme example and almost every nail and iron peice had a iron blood stain around it..

 

[HumblePie]

Thanks James...geez, this is all real good info; it all adds up to give a better picture of how this machine identifies iron. For my purposes, iron bars are a d@mned nuisance; while I don't expect to eliminate them, I'd at least like to be able to ID them from various large ores and save some digging----and be able to do this using one machine (hopefully F-75) instead of the two I currently have to lug around up in mine country in order to actually do some efficient (not wasting time diggin' iron) prospecting. It's a shame that some manufacturer won't build a complete detector suitable for prospecting (and just about everything else for that matter) that incorporates a signagraph type circuit (as well as full range discrimination) to go along with the depth capability of the F-75, in a lightweight format like the F-75 and many others now available. The technology has been in place for at least 16 years that I'm aware of. This is why I'm asking all these questions about iron ID.
Speaking of pictures, you have some dandies that really illustrate what you were dealing with on site. I'm a bit surprised that the nails read so high, but as you say, at the time you had a lot on your mind, so maybe didn't pick up on some iron sounds the discriminator was providing in addition to the visual not necessarily locking on.
Something else, a bit off topic, but you mentioned arbitrarily lowering your ground balance quite a bit from the true ground balance. This is going to significantly reduce your ability to punch deep and make the detector much less sensitive as well. Granted, it'll still easily pick-up large (esp.iron) targets, but I guess I don't understand what this is trying to accomplish.
Meanwhile, if anything else comes to mind about id'ing iron, please give me a shout. Appreciate all you help...Jim.

 

[digitrich]

Hey Charlie, where you using the stock coil?? Bet the results would be better with the smaller coil. But a 6 inch spike, that's a whole lot of metal to ignore, I'd imagine. Thanks for the info.

 

[Charlie P. (NY)]

Yep. Stock 11" flounder skeleton.


Coins fear me.

 

[liquid1]

Hey humblepie..I also tried using the small coil for a bit same tones..With all the Iron the ground matrix was eat up..I did find a small piece of wire not much bigger than a strand of hair close to 8" deep..as for the ground balance I am still learing how to get a good manual ground balance
Nasa toms dvd shows a good demistration ..I posted a question about the hi tone falseing on his forum he said I might need to over drive the GB in my extreme conditions and make sure i was clear of metal..I noticed Bill ladd hunts alot in all metal ..the F75 is full of options and features and I want to get every relic possible so Digging the Iron of old wagon and tractor parts was pretty cool..I cant wait to go back..

 

[HumblePie]

James...thanks for getting back to me. Sounds to me like you doing just fine, getting small wire at 8 inches in your soil. For ground balance, follow the instruction in your manual so that there should be no difference in the sound as you lower and raise the coil (up to say, half a foot off the ground); if you can't quite get an exact ground balance, you might consider lowering your sensitivity down a bit to be able to achieve GB more easily...mainly because you have described the mineralization in your area to be fairly high, while this unit is very sensitive. Be sure to GB in an area that's free of any metal by scanning it first in all metal.

Once you have a reasonable GB, you might consider increasing it by 2 or 3 digits to get a slightly audible response as you lower the coil to the ground. This technique should also help decrease ground mineral induced instability and help with slightly better depth on small targets. It amounts to "overdriving" the ground balance somewhat, and is often described as "adjusting for positive response to the ground matrix".

On the other hand, if you experience positive "hot rocks" in any quantity while hunting in the all metal mode.. that interfere too much with your detecting, this would be a circumstance where you might want to decrease your GB just a bit to reduce or even eliminate the pesky rocks. Remember..positive hot rocks have a lower ground balance setting than the immediate area for which you've set the real ground balance; so if you ever do want to make this type of adjustment, keep in mind that you will then be slightly underbalanced to the immediate area you're hunting. The other obvious choice is to switch back over to a discriminate mode with some small amount of iron discrimination dialed-in and that generally will solve the problem too.

When you go back to the iron infested area and get a high tone, try raising your coil and see if that helps to get a better ID on big iron. Appreciate it if you'd let me know what happens...thanks...Jim.

 

[liquid1]

Thanks for the great info for GB...I will take these notes into the field..I researced metal detectors for several months and wanted a machine i could learn and
grow into, and with all the rave reviews with recovery speeds and depths I chose the F75..Its Fast !!!!! with both coils..It is a sweet amazing machine..I just ordered my dad and my 11 year old daughter the fisher
F2 unit..so we all will be hunting toogether soon..Jim I will try out the above suggestions and take notes.thanks again fors the tip..james

 

[HumblePie]

James...the F-75 does seem to me to be quite a useful unit, it's definitely the leading contender on my short list for a new VLF to use for shallow prospecting, plus the overall capability for other uses as well. I guess you could say that I'm very cautious, and determined to reasonably learn all I can prior to making a purchase. I've already looked into other machines, but left the F-75 as the last VLF unit to research for two reasons: I just like the units qualifications better than others, and I wanted to hear opinions from users. There is no substitute for experience.

Meanwhile James, I did not know if you were all that interested in hearing about ground balance manipulations (and hot rocks) but since you seem to want some info, hear is a more complete explanation..as I understand it.

Hot rocks are iron mineralized rocks with a different ground balance setting from your detector setting. Hot rocks repond either positive with a metallic "zip zip" or negative with a "boing" sound. The positive rocks require reducing the ground balance (decreasing the sound as you lower your coil to the ground) to silence them...which leaves you underbalanced for the general matrix. In an area where there are just too many to ignore, sometimes you are obliged to quiet them down with a partial ground balance adjustment (decrease GB)..it's a trade off.
The negative hot rocks require an increase in ground balance (increasing the sound as you lower your coil to the ground) to silence them...which leaves you over ground balanced for the general ground matrix you're hunting in.
Since negative rock sounds are readily identifiable, you can easily ignore them for what they are. Also, without auto retuning (SAT, Autotune...) these rocks would not give any kind of response in terms of increased sound. In fact they would cause your detector to go quiet as the coil passes over them. With autotune, the "boing" you hear is the result of autotune trying to readjust the threshold, but "overshooting" into an audible sound briefly.

Regardless of whether you slightly increase or decrease the ground balance, the sensitivity impact on your relic hunting targets will be minimal really. It

 

[liquid1]

Thanks for the info It gives me a much better understanding of how to set up the machine for conditions..The land that me and my family is hunting
has had a few small gold nuggets pulled from the creek about 2 year ago according to my dad..its his land..And theres
lots of Iron ore around...errr... about 1/2 mile down the road theres an old plantation that had a Iron ore Boiler so I think I am in prime Relic country..Most folks that seem to get the old coins and finds seems to be using the F7 Freq default is F4 is this due to picking up smaller Items..The area is littered with the square nails for sure..I was really suprised at all the Iron thats burried out there..I have heard the boing boing and sipp zipp when I dugg up what I think might be a meterorite particle at a local old park..I was in all metal mode found a Iron Stob with a logging chain welded to it, a good 14" deep.. So I know the F75 is going deep..I'm still not sure what it was, I was in the middle of a field..I seem to like the JE mode discrim 3-6 ,sense as hi as it will run 30 is still good..F7 The JE mode the tones seem to be amplified they sorta jump out at ya..I will deffinatly try the Manual GB in all metal and do some testing vs the fast grab.
cool stuff and info..

 

[HumblePie]

James...you are welcome...it gave me a chance to help out a bit for all you've done for me. Wouldn't hurt for you all to head down to the creek, and have some fun with that detector by checking on the downstream side of the inside of the bends for increased black sand using your Iron Oxide graph. When you do, you and your folks could have a lot of fun with a shovel and goldpan. Just dig down to the hardpan, or hard substrate.. that's where any gold will be; also if the stream has cut out some decent banks, you might either try (a) a little nugget hunting in your all metal motion mode, sensitivity as high as stability allows, faint hum for threshold, and manual ground balance then increase the setting by 2or3, or, (b) try sampling the same inside bends but from the bank itself, shovel some likely looking spots into a bucket, take it down the stream, sit down comfortable-like, and pan it out..just to see.

If there's lots of iron ore around, chances are you're also in prime hot rock country too!! Keep in mind that any rock with quartz and any other unusual material attached is worth taking a closer look. It may not be a hot rock, but something a little more interesting.

You mentioned using the F7 frequency option, that somehow it may be related to getting the older, deeper coins and finds. The only possible explanation is if there's electrical interference in the area that the F7 frequency setting quiets down enough to make it easier to hear the deeper signals...doesn't seem likely, but possible. While the F7 setting is a slightly higher frequency than the default setting, it's not significant enough to really increase sensitivity to low conductives like gold jewellery; and keep in mind that older, more valuable coins are composed primarily of either silver or copper...higher conductives; further, it's the lower frequencies that tend to penetrate better especially in mineralized soils (like your area); my understanding is that VLF metal detectors operating at lower frequencies generally perform better in terms of ground cancelling as well. Soooo...if its a fact the F7 frequency setting somehow is doing better, I can't explain it beyond reducing any electrical interference in the area.

Last thing, the JE mode is entirely in high gain (whereas the DE mode kicks in high gain with disc setting below 5 or above 19), so it's very sensitive. I wonder if that's why the tones seem to jump out at you. Well it's late and I gotta get to bed in decent time today sort of (it's a wife rule). Geez, I enjoy yakking about detectors and stuff. You relic hunters would soon have me converted I guess. So long and thanks...Jim Hemmingway.