reddirtfisher
New member
When I put an old rusted nail on top of a nickel and try to detect it....I get nothing. It is the same for all my units from different companies.....Is this normal ?
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Iron Masking ?
- Thread starter reddirtfisher
- Start date
When I put an old rusted nail on top of a nickel and try to detect it....I get nothing. It is the same for all my units from different companies.....Is this normal ?As the title of your post suggests, that's called "iron-masking". The discrimination is seeing the object on top (which its been instructed to discriminate out), hence missing the object underneath it. And even if the nickel weren't *exactly* underneath the nail, (and was merely besides it), the same phenomenom could occur (or variations of sloppy unclear chopped up signals).
Some machines are better at seeing objects close together. That is known as the ability to separate. But when the objects are truly co-mingled (the nail squarely on TOP of the coin), then you have to have a machine that is good at seeing through (aka "averaging").
So while you might not get a "nickel" TID signal, yet you could tell that there's a conductive target there. It will depend on the size of the nail by the way. Or that if you added a 2nd and 3rd nail, you eventually get to the point where you can no longer hear the coin.
Typically 2 filter machines do the "averaging" trick best. That would be machines like the Silver Sabre, Shadow x2, Whites classic series, etc.... Or if you really want to go all out, find a Compass 77b (circa early 1970s all-metal TR technology). They could see a coin with up to 3 nails over the top But ..... any machine that's good at this trick, will tend to lack depth, lack ability in minerals, etc... And conversely, power-house deep seeker great TID machines will tend to do more poorly in the "see-through" department.
Some machines are better at seeing objects close together. That is known as the ability to separate. But when the objects are truly co-mingled (the nail squarely on TOP of the coin), then you have to have a machine that is good at seeing through (aka "averaging").
So while you might not get a "nickel" TID signal, yet you could tell that there's a conductive target there. It will depend on the size of the nail by the way. Or that if you added a 2nd and 3rd nail, you eventually get to the point where you can no longer hear the coin.
Typically 2 filter machines do the "averaging" trick best. That would be machines like the Silver Sabre, Shadow x2, Whites classic series, etc.... Or if you really want to go all out, find a Compass 77b (circa early 1970s all-metal TR technology). They could see a coin with up to 3 nails over the top
But ..... any machine that's good at this trick, will tend to lack depth, lack ability in minerals, etc... And conversely, power-house deep seeker great TID machines will tend to do more poorly in the "see-through" department.reddirtfisher
New member
Thanks for the input Tom. I guess it is just another one of those problems (like pull tabs) that we all have to deal with.
You can also get the same problem when using larger coils as in if the coil is over say 2 good targets but iron is also under the coil at the same time once again the discrimination will 'null' the good targets out.Another massive problem that can also happen with some modern coinage as in Canadian and UK coins not all coins i will admit,some have a iron cores so once again the detector discriminates these modern coins out as well.
So yes these are some of the problems that we face,this is why its advisable only to use a really big coil on a VLF machine if the ground is seen as pretty clear other wise you can loose decent targets.
So yes these are some of the problems that we face,this is why its advisable only to use a really big coil on a VLF machine if the ground is seen as pretty clear other wise you can loose decent targets.
reddirtfisher
New member
I dusted off my Bounty Hunter DE 280 VLF/TR D ( 1984 ) model and tried it too. Guess what ? It picked it up with no problem !!
...go figure....it did it just like the old Compass 77b. Sometimes you just can't beat the older machines and they will really surprise you. 
reddirtfisher said:
The old Compass 77b detector is a very sought after detector for specific sites over here in the UK,it may be old but it certainly performs very well on our trashy roman sites and also the Thames foreshore as it is favoured by the Mudlarks especially because of what you have just found out.
reddirtfisher said:
Does that machine ID the target or just say it is metal?
reddirtfisher
New member
The Bounty Hunter DE 280 does not have target ID but it does have a really cool built in discrimination feature that somehow knocks out most of the junk targets and still gets the gold rings. It will still pick up the most recent modern day square pull tab,...but nothing else. These come up for sale sometimes of Fleabay ....I don't know if the Compass has ID or not....
Don't confuse those 2 types of TR mode. The one you speak of on your Bounty Hunter's VLF/TR , was a TR discriminate. The TR on the old 77b, was an all-metal TR.
But it gets confusing: Because on some of the TR disc. units of the different makers back in the 1970s, you could indeed turn down the disc. control SO low, that it did mimic the all-metal TR. That is to say, that both would knock out individual nails, yet see through them. However, other TR disc's lowest setting did not go down that low. I mean, it went down low enough to accept foil perhaps, but still high enough to knock out a RR spike, pair of rusty pliars, etc.... Contrast to the 77b, where larger iron like a RR spike comes in (yet you can tell by audio clues that it's not a conductive target). So it depended on which particular TR disc. you had , as to whether you could do the "hat trick" or not.
Example: Try these tests: raise the disc. on that bounty hunter, so that you only knock out iron, yet still get even teeennnssy foil (is that possible?), and then do the test. Perhaps it will pass the "nail-see-through" test at that point. Now do it with knocking out gum wrappers, then pull tabs, and so forth. I believe you will find that the minute you start to progress the disc. knob upwards, you can no longer do the hat-trick. It only works at the lowest settings (to take advantage of the averaging effect), and only then-so, on some TR disc's, depending on the stock factory calibrations.
But it gets confusing: Because on some of the TR disc. units of the different makers back in the 1970s, you could indeed turn down the disc. control SO low, that it did mimic the all-metal TR. That is to say, that both would knock out individual nails, yet see through them. However, other TR disc's lowest setting did not go down that low. I mean, it went down low enough to accept foil perhaps, but still high enough to knock out a RR spike, pair of rusty pliars, etc.... Contrast to the 77b, where larger iron like a RR spike comes in (yet you can tell by audio clues that it's not a conductive target). So it depended on which particular TR disc. you had , as to whether you could do the "hat trick" or not.
Example: Try these tests: raise the disc. on that bounty hunter, so that you only knock out iron, yet still get even teeennnssy foil (is that possible?), and then do the test. Perhaps it will pass the "nail-see-through" test at that point. Now do it with knocking out gum wrappers, then pull tabs, and so forth. I believe you will find that the minute you start to progress the disc. knob upwards, you can no longer do the hat-trick. It only works at the lowest settings (to take advantage of the averaging effect), and only then-so, on some TR disc's, depending on the stock factory calibrations.
You guys in England have something that's still currently being made, if I'm not mistaken, that mimicks the 77b's ability in that regard. At least the last time I looked, it was still being made. It's called the "Viking" detector, right ? Very much like the 77b (if not identical) with a few modern whistles and bells added (depending on exactly which Viking model you get).
They are often seen as childs-toys beginner models. Because they lack depth, lack any other form of ID, don't fare well in minerals, etc... etc..... So unless you had some super iron-nail-riddled site, these would be dinasours. But if you had some carpet of nails, and depth wasn't the only objective, then these would be the same function as the 77b.
They are often seen as childs-toys beginner models. Because they lack depth, lack any other form of ID, don't fare well in minerals, etc... etc..... So unless you had some super iron-nail-riddled site, these would be dinasours. But if you had some carpet of nails, and depth wasn't the only objective, then these would be the same function as the 77b.
Tom_in_CA said:
Tom,that rather interesting,just had a look at the Viking website,do you have any idea which model it is please mate ??? they are one of the oldest makers in the UK but also possibly one of the least popular,if you have any further information on what model it is that is similar to the 77b i could well give it a try.
Thanks for the heads up on that one.
Dancer
Well-known member
Beach hunting with a Pulse Induction, quite a few times scooped up a nickel with pull tab. Of course, this is the area of gold rings. (Unfortunately) Depending on the amount of trash, I have mudhunted with this machine, 8"coil. This after the area was combed over with vlf's. This has resulted in a few good finds, the last of the nickels, and of course, all the alum. I can stand.
Few days ago I was reading about a machine that will ignore clad, and see silver beneath. I guess if your hot on silver, short on time , might be worth a look.
Maybe I'm a dinosaur, but if I have a site that I think has something I want, well it's going to get a good thrashing.
Few days ago I was reading about a machine that will ignore clad, and see silver beneath. I guess if your hot on silver, short on time , might be worth a look.
Maybe I'm a dinosaur, but if I have a site that I think has something I want, well it's going to get a good thrashing.
Mega B said:
Mega-B: The last I looked at their offerings, they were all the same thing: All-metal TR's. The only difference was, as you bought the "step up" models, was just more whistles and bells. For example, the lower priced ones were just a single knob or whatever. Where the on-off also doubled as the tuner, and had a pre-set sens, blah blah (so that would've been similar to the Compass coin-hustler model I suppose). And perhaps the more expensive Viking's had an adjustable auto-tune feature, to "hug" the ground (not to be confused with ground balance as we know it today). And perhaps the more expensive ones had intensity meters, blah blah. But in essence, they were all the same, insofar as they are all-metal TR's.
I'm not sure if they've added anything to their line-up in recent years. And as for them being the least popular in sales, well ..... go figure: In nearly every way, this technology went the way of the dinasours back in the mid to late 1970s. By the late 1970s and through the '80s, you could get 3x the depth, while discriminating, ground balancing, and now TIDs as well! So why would ANYONE ever want to go back to this ancient technology ? But for the once specific niche of seeing through iron, is where this excels. So for things like sidewalk tearouts, or needing to stick your coil underneath wooden porches, etc....