Masking, something everyone should know

[EZrider]

Behind the mask
I know a lot of vets already know this but I figured there was always new people that should know this. What I'm going to cover is Masking and Silent Masking

What you need, clad dime, 16 penny nail or iron flat washer. Your detector.

Here is what you do. Find a clean spot in your yard say 2’x2’ and use your detector to clean all metal from that area. Now in the center bury your dime 5 inches deep. Cover it up and run your detector over it to make sure you hear it.

Masking: Now take your iron and wave it past your coil. You should hear a low tone. If not set your detector up so you can hear iron. No Discrim or notching. So you can hear both iron and your buried dime. Now take your iron and place it about 2 inches away from the center of where your dime is and pass your coil over it. The only thing you will hear is the iron, this is masking.

Silent Masking: Now pick up your iron and set your detector to Discrim out iron and wave it past your coil. You should hear nothing. Now pass your coil over the dime, yup its there. Again set the iron 2 inches away from the center of where the dime id and pass your coil over it. What do you hear? Nothing, this is silent masking.

 

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[vickilynn]

Hi ,
Newbie here! , one question. What does all that mean? I am new at mding and want to learn it all hopefully you might know blonde-english? lol
Vickilynn

 

[Tom_in_CA]

Vickilynn, in laymen's language, masking is where your machine rejects whatever it is you discriminate out (nails, foil, etc... Wherever you set your controls), and the machine correctly discriminates those objects out. However, a coin (or whatever desirable object) UNDERNEATH (or in real close proximety, etc...) also will get rejected, because the detector "sees" the bad object, and thus the good object is "masked" by the bad object.

 

[Sandman]

This Masking does not take place with Minelab's Excal and Sov GT with Iron Mask on. You can still hear the dime under the nail.

 

[George W]

I must be missing something in both tests with iron close to the dime you say you hear nothing. Then what is the point of this post? I mean I was all set for you to explane how you can hear the dime over the iron.. Please explain! Thanks! George


Behind the mask
I know a lot of vets already know this but I figured there was always new people that should know this. What I'm going to cover is Masking and Silent Masking

What you need, clad dime, 16 penny nail or iron flat washer. Your detector.

Here is what you do. Find a clean spot in your yard say 2’x2’ and use your detector to clean all metal from that area. Now in the center bury your dime 5 inches deep. Cover it up and run your detector over it to make sure you hear it.

Masking: Now take your iron and wave it past your coil. You should hear a low tone. If not set your detector up so you can hear iron. No Discrim or notching. So you can hear both iron and your buried dime. Now take your iron and place it about 2 inches away from the center of where your dime is and pass your coil over it. The only thing you will hear is the iron, this is masking.

Silent Masking: Now pick up your iron and set your detector to Discrim out iron and wave it past your coil. You should hear nothing. Now pass your coil over the dime, yup its there. Again set the iron 2 inches away from the center of where the dime id and pass your coil over it. What do you hear? Nothing, this is silent masking.

 

[BuckleBoy]

I must be missing something in both tests with iron close to the dime you say you hear nothing. Then what is the point of this post? I mean I was all set for you to explane how you can hear the dime over the iron.. Please explain! Thanks! George

The point of the post is that if your detector is susceptible to this, then you have to dig out all the big iron, and go slow in iron patches in order to hear all the good finds.

If you reject iron, and your machine falls victim to silent masking, you won't even hear that Seated Liberty Dime under all the iron.

-Buckles

 

[greydigger]

I saw a scale somewhere as to what gets discriminated out -
maybe like first iron, then dimes, then gold etc. as you turn up the disc.
Anyone know that scale?

 

[George W]

Buckles,
Thanks for the reply! Ok I think I get it now.. The post was to see how much masking will effect your particular detector.. I run a DFX I reject from -95 to -40 and accept -41 to +94 and reject +95.. I'm going to run the test myself and see. I was running bottle cap at 5 but will lower it to1 and see if that helps..Anyone know how much masking a DFX will see with the setting I use? Thanks! George

 

[Shortstack]

To Vikilynn and George W.

Get the book DETECTORIST, A How-To Guide to Better Metal Detecting, by Robert H. Sickler. I THINK he updated with a later writing, but even his first edition is excellent. His tips and techniques are very usable and understandable for newer hobbiests.

 

[George W]

Shortstack,
Thanks! I'll get it and check it out!! George

 

[Treasure Tom]

Sandman,

Will the 2 Minelabs still detect a coin if it was directly under a coin size iron object? Are there any detectors that can actually pick up a non-iron object which is beneath a larger iron object? Thanks!

Tom

 

[Tom_in_CA]

Sandman, I beg to differ with you: The Excaliber and Sovereign, will indeed mask, when you put iron over a coin, no matter how you set up the Excal or Sov. Try it and see. Set up your controls to knock iron, in whatever fashion you choose. Now put a healthy sized nail over a coin, and I bet you get the reject and/or cr*ppy sound, right?

Treasure Tom: The only machine that can see through several nails at a time, was the old TR all-metal technology (not to be confused with TR disc). They could pick up coins right under nails, yet not pick up the nails sitting alone. Trouble was though, they lacked depth, were a bear to keep balanced, worked poorly in mineralized soil, and had no other form of disc. (ie.: foil and silver dollars all sounded the same). But to this day, those old TR all-metals work well in nail riddled ghost towns. The Compass 77b was a good example of this. You can find them on ebay for $70-ish to $100-ish from time to time. They were made from the early to mid 1970s.

 

[Treasure Tom]

Thanks Tom in CA, always thought detectors would have problems identifying objects especially when there is a lot of iron around. So, if there was a cache of coins in a metal container, then the detector would probably give you an iron signal..right?

Tom

 

[Sandman]

"The Iron Mask switch is a throwback to the original Sovereign. Iron Mask was introduced back in 1991. This circuit – not found on any other brand of detector – allows for coins, relics and other valuables to be detected even if there is a ferrous target lying next to it. " This is from the field test of the Sov GT. To much sens cancels this out.

A cache of coins in a Iron container would not respond with the coin sound. Due to the size of the container it probably would not null out either but sound with the low iron tone due to the size of the container.

Tom in CA, To make sure I wasn't mistaken I tried this with the Sov GT, Iron Mask on and a disc setting of zero. It nulls on the iron nail and responds to the dime. Sensitivity was set in auto.

 

[Dave45]

I run the quattro in all metal in hi iron areas and it will drive you crazy with all the ferrous sounds, I was thinking why cant they just cancel out the sound just the sound, not the detectors ability to pick up the iron just the sound, maybe a set of headphones could do this.
If this were developed you'd make a mint and could be used on any detector.
Dave

 

[George W]

Dave,
A DFX can do just that!! You can cancel out the sound while still seeing iron on the display.. There are so many detectore out there it's hard to know the strong and weak point to them all.. I felt the DFX would give me more flexibly in the way I would like to to respond.. George

 

[Tom_in_CA]

Sandman, re-read your posts: First you said you can see coins *under* (ie.: through) nails, with your Sov. But in your second post, you see coins lying *next to* nails. There is a big difference. Yes, some machines do good at target separation (when objects are close-by each other, but not under the other). I don't believe the Sov or Excal will see through iron. You may get an iffy tone that you might want to investigate, at best.

 

[Sandman]

Sandman, re-read your posts: First you said you can see coins *under* (ie.: through) nails, with your Sov. But in your second post, you see coins lying *next to* nails. There is a big difference. Yes, some machines do good at target separation (when objects are close-by each other, but not under the other). I don't believe the Sov or Excal will see through iron. You may get an iffy tone that you might want to investigate, at best.

Yes Tom, I went back outside to try it again and the Sov does pick up a nickel under a 6 penny nail. Granted the sound is different, but one I would still dig. I made sure the ground under the test targets was clean too. I tried some different settings and at higher disc the nickel and nail were silent as I knew they would be. Tried different directions too. Only used a nickel, not any other coins.

Do you have a Sov or Excal to try this experiment yourself? I thought I might be all wet and didn't want to give the impression I didn't know what I was talking about so I asked CJC about this too. Guess a lot also depends on the "angle of attack" or minerals where the targets are located too.

 

[Tom_in_CA]

Yes I ran around with an Excaliber for years (still do sometimes). If the beach were nail-ridden (like after a storm) we could in-no-way see through nails. It would null over them, and mask anything that was beneath them. Yes, even at the lowest disc. settings, etc... Interesting that you say 2 things: 1) "it depends on angle of attack" Yes, because there are infinite variations of how much of a peak is "showing" how close the two objects are (like, especially if they are touching), etc... and 2) you say the "sound was different" (when you tested it). Yes, machines that mask often don't get 100% reject sound, but on the other hand, you're certainly not "seeing through", as if the object wasn't there. Yes, when you're demolition site or ghost-town type hunting, you're probably going to dig even the remotest of signals, that could be stuff trying to average through, etc... But when you compare THAT to something like the 77b, there is a difference.

Have you tried the 77b? Oddly, a nickel (low conductors) will work the best for the test. So for example, you could pile 4 nails over a nickel, and ... doing it right .... still get a conductive tone. But for a dime in the same test, it may only allow for 3 nails, before nulling out. Dunno why a lower conductor would fare better in this all-metal-TR test. Maybe a techno-buff can answer that? So try your test with a penny and dime, and see if they get through a nail too. Ie.: maybe it only peaks through with low conductors, like the 77b tended to do better?