Sensitivity and Detection Field Width

Huckleberry

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Feb 11, 2021
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Missouri Ozarks
Sorry if this has been asked before, if so I was unable to find it. I'm working on this ridiculously iron infested site (along with the usual garbage), and was wondering if lowering the sensitivity would narrow the detection field on a DD coil, and if so, how narrow a detection field would be realistically possible. I assume that narrowing the detection field would increase target separation? This question specifically relates to the Fisher F75. Anybody know? :?:
 
You as the operator cannot adjust the “width”. On a machine where you cannot adjust the transmit (TX) power, the field size/shape is fixed by the size and configuration of the coil. The sensitivity control will dictate how small or “detectable” anything ferrous or non-ferrous is within that field.
 
In disc go to 40 or below on the gain, 30-35 would even be better.
You actually will still get pretty deep, (the power range in this thing is not actually 1-99), but even using a bigger coil target resolution gets better and this seems to fool your detector into thinking you are using a laser-like fine sniper coil and targets will pop up like there are little red flags over them.
I have used this a bunch in areas that frustrated me like in heavy iron or massive trash like around picnic pavilions.
Pretty shocking when you see this happen in the field.
Don't know why this works...it just does.

I use this method mostly in heavy trash, for extreme iron I found a different method that works even better, I call this the Blast Through Method.
https://metaldetectingforum.com/showthread.php?t=196462


It is the opposite of that low gain way of doing things but again...on Fisher units hunting in heavy iron more gain actually gets you even better resolution than lower gain which is opposite thinking using many detectors.
The high beams don't work near as well in fog as lower beams way of thinking.which on Fishers this is just not true.
This is a real thing, NASA Tom knows it because he has commented on this technique in the past and as I continued to use it over the years I got better and better at it and found tons more in sites so infested with iron you would be shocked.
It also works in heavy mineralized dirt shockingly well which I have in spades.
This is my number one way of hunting here when I pull out my Fisher.
It took awhile to get used to it and learn to notice the exact the behavior I am looking for but now it is second nature to me and I have been super successful using it over all other methods.

Motion all metal, turn the gain all the way up to 99 and max out the threshold, too.
Not sure if DST will affect anything so try it on and off and see.
I use the F70 which doesn't have that so with no DST less filters I have to work with, (or against), and this method works fantastically great without it.

It will be ultra jumpy, schizophrenic and noisy, the biggest part about learning this method is getting used to all that but if you can, and once you do, the sky is the limit.
Use any coil you want but move slow, watch for a range of numbers that repeat, not just a few like using regular disc but more like a range of 6 or so.
If you get big drops out of that range way lower as you slowly move the coil around a small area just move on but if you can keep it with that smaller range then see if you can get the same behavior coming at the target from a different 90 degree direction.
If you can great but not done yet, you need to make sure you are over an actual target and not just getting a false high tones being thrown off by iron in the vicinity that will happen often using these settings.
Notice the area where the target seems to be and move the coil away then hit the pinpoint trigger then move back in to target center.
If there is no target at that area but one seems to be a few inches away this is going to be iron falsing in that target area so move on.
If there is a target in that exact location and you continue to get that higher range of numbers that aren't dipping down into iron dig that target...it will most likely be something non ferrous.
Might be something good like a coin or it could be something else but there should be a non ferrous target down there that might or might not be near actual iron but something else besides iron should be down there.
Get good at this technique and eventually you will be able to identify non ferrous targets at will no matter how much iron you are dealing with.
Sounds weird, totally different than what most of us know as hunting normally but if you can wrap your head around it and learn to hunt this way in iron your skill set will be enhanced greatly and it will pay you major dividends going forward.
It sure has for me for years.
 
In disc go to 40 or below on the gain, 30-35 would even be better.
You actually will still get pretty deep, (the power range in this thing is not actually 1-99), but even using a bigger coil target resolution gets better and this seems to fool your detector into thinking you are using a laser-like fine sniper coil and targets will pop up like there are little red flags over them.
I have used this a bunch in areas that frustrated me like in heavy iron or massive trash like around picnic pavilions.
Pretty shocking when you see this happen in the field.
Don't know why this works...it just does.

I use this method mostly in heavy trash, for extreme iron I found a different method that works even better, I call this the Blast Through Method.
https://metaldetectingforum.com/showthread.php?t=196462


It is the opposite of that low gain way of doing things but again...on Fisher units hunting in heavy iron more gain actually gets you even better resolution than lower gain which is opposite thinking using many detectors.
The high beams don't work near as well in fog as lower beams way of thinking.which on Fishers this is just not true.
This is a real thing, NASA Tom knows it because he has commented on this technique in the past and as I continued to use it over the years I got better and better at it and found tons more in sites so infested with iron you would be shocked.
It also works in heavy mineralized dirt shockingly well which I have in spades.
This is my number one way of hunting here when I pull out my Fisher.
It took awhile to get used to it and learn to notice the exact the behavior I am looking for but now it is second nature to me and I have been super successful using it over all other methods.

Motion all metal, turn the gain all the way up to 99 and max out the threshold, too.
Not sure if DST will affect anything so try it on and off and see.
I use the F70 which doesn't have that so with no DST less filters I have to work with, (or against), and this method works fantastically great without it.

It will be ultra jumpy, schizophrenic and noisy, the biggest part about learning this method is getting used to all that but if you can, and once you do, the sky is the limit.
Use any coil you want but move slow, watch for a range of numbers that repeat, not just a few like using regular disc but more like a range of 6 or so.
If you get big drops out of that range way lower as you slowly move the coil around a small area just move on but if you can keep it with that smaller range then see if you can get the same behavior coming at the target from a different 90 degree direction.
If you can great but not done yet, you need to make sure you are over an actual target and not just getting a false high tones being thrown off by iron in the vicinity that will happen often using these settings.
Notice the area where the target seems to be and move the coil away then hit the pinpoint trigger then move back in to target center.
If there is no target at that area but one seems to be a few inches away this is going to be iron falsing in that target area so move on.
If there is a target in that exact location and you continue to get that higher range of numbers that aren't dipping down into iron dig that target...it will most likely be something non ferrous.
Might be something good like a coin or it could be something else but there should be a non ferrous target down there that might or might not be near actual iron but something else besides iron should be down there.
Get good at this technique and eventually you will be able to identify non ferrous targets at will no matter how much iron you are dealing with.
Sounds weird, totally different than what most of us know as hunting normally but if you can wrap your head around it and learn to hunt this way in iron your skill set will be enhanced greatly and it will pay you major dividends going forward.
It sure has for me for years.

Thanks Digger27! Copied and pasted. It looks and sounds like we hunt the same kind of sites. I am trying to wrap my mind around this, and will certainly try to learn this method! As you say, it is opposite of what I am used to doing, but as soon as the weather allows, I'm going to give this a shot. Again, thanks for your help, it is much appreciated.
 
Give it a shot, can't hurt...might help.
I tried this for several hunts at that site I mentioned in that link.
At first I was totally lost but as I kept at it I started noticing that better behavior more and more.
After several hunts it all finally clicked and I have been using that method now for years.
I hunted using a DD sniper, the 11" DD and a 10" elliptical concentric at different times and they all worked and for me it was a bit easier and more efficient to notice the good signals using the DD sniper but you choose your favorite.
 
In disc go to 40 or below on the gain, 30-35 would even be better.
You actually will still get pretty deep, (the power range in this thing is not actually 1-99), but even using a bigger coil target resolution gets better and this seems to fool your detector into thinking you are using a laser-like fine sniper coil and targets will pop up like there are little red flags over them.
I have used this a bunch in areas that frustrated me like in heavy iron or massive trash like around picnic pavilions.
Pretty shocking when you see this happen in the field.
Don't know why this works...it just does.

I use this method mostly in heavy trash, for extreme iron I found a different method that works even better, I call this the Blast Through Method.
https://metaldetectingforum.com/showthread.php?t=196462


It is the opposite of that low gain way of doing things but again...on Fisher units hunting in heavy iron more gain actually gets you even better resolution than lower gain which is opposite thinking using many detectors.
The high beams don't work near as well in fog as lower beams way of thinking.which on Fishers this is just not true.
This is a real thing, NASA Tom knows it because he has commented on this technique in the past and as I continued to use it over the years I got better and better at it and found tons more in sites so infested with iron you would be shocked.
It also works in heavy mineralized dirt shockingly well which I have in spades.
This is my number one way of hunting here when I pull out my Fisher.
It took awhile to get used to it and learn to notice the exact the behavior I am looking for but now it is second nature to me and I have been super successful using it over all other methods.

Motion all metal, turn the gain all the way up to 99 and max out the threshold, too.
Not sure if DST will affect anything so try it on and off and see.
I use the F70 which doesn't have that so with no DST less filters I have to work with, (or against), and this method works fantastically great without it.

It will be ultra jumpy, schizophrenic and noisy, the biggest part about learning this method is getting used to all that but if you can, and once you do, the sky is the limit.
Use any coil you want but move slow, watch for a range of numbers that repeat, not just a few like using regular disc but more like a range of 6 or so.
If you get big drops out of that range way lower as you slowly move the coil around a small area just move on but if you can keep it with that smaller range then see if you can get the same behavior coming at the target from a different 90 degree direction.
If you can great but not done yet, you need to make sure you are over an actual target and not just getting a false high tones being thrown off by iron in the vicinity that will happen often using these settings.
Notice the area where the target seems to be and move the coil away then hit the pinpoint trigger then move back in to target center.
If there is no target at that area but one seems to be a few inches away this is going to be iron falsing in that target area so move on.
If there is a target in that exact location and you continue to get that higher range of numbers that aren't dipping down into iron dig that target...it will most likely be something non ferrous.
Might be something good like a coin or it could be something else but there should be a non ferrous target down there that might or might not be near actual iron but something else besides iron should be down there.
Get good at this technique and eventually you will be able to identify non ferrous targets at will no matter how much iron you are dealing with.
Sounds weird, totally different than what most of us know as hunting normally but if you can wrap your head around it and learn to hunt this way in iron your skill set will be enhanced greatly and it will pay you major dividends going forward.
It sure has for me for years.

So, I’ve had the opportunity to use the F75 a handfull of times now, and have tried both of your methods. The low gain method worked quite well in the schoolyard, and managed to squeak a few coins from my quite pounded iron infested yard as well. Unfortunately, all clad.

Now I am not an expert, astute, or even an advanced detectorist. Probably more middle of the road, old guy hobby detectorist. I do have 3+ years with the Tracker, Sharpshooter and Liberator, and hope that I am not completely stupid.:?: So with that said, I have questions regarding the Blast Through Method that you described. (I have read your information as well as Nasa Tom’s Compilation #1, and #2 (multiple times)) to try to get a grip on this advanced method. (Maybe I’m pushing the learning curve a bit???) Anyway, specifically regarding maxing out the threshold, would this be +9 or -9? This is my first detector with threshold capability, however, (again this is the traditional way of doing things) I had previously been led to believe that thresh should be “mosquito hum” so as to not eliminate weak signals. At +9 thresh it is quite a loud hum, so am I correct in my assumption that this level of thresh is blocking out those weak signals? Or am I continuing to look at this method wrong? I would really like to get this under my belt, as it seems that all of the old sites around here are where nails go to die!
 
I get the moderate threshold hum thing, I used a Vaquero for several years too and tried it all different ways but lower thresholds seemed to work the best...for me in my dirt.
Supertuning is what we called it when we pushed the thresh past that tiny gnat in your ear buzz that Tesoro always recommended, that would get you deeper and would equalize all target sounds if you used it.
Like a coin at 2" and another at 6 -8" could sound the same with the same volume level...you basically lose all modulation and the ability to judge depth although the hum never actually got loud enough to drown everything out even at maxed levels.
As far as busting up the thresh on my F70 or the F75 if you are able to do that in all metal it always seemed to work the best for me using this blast through method.
Don't know exactly why, it just seems to isolate non ferrous targets better at all depths once I noticed the patterns and behavior I saw happening over non ferrous good targets.
Might not need to max it out to +9 either like I usually do but I would stay at +4 and above which might also work well.
Raising the thresh on these units doesn't really increase any hum all that much, what it does do is skew the sound of the tones a bit and push the threshold limit down where you can hear targets deeper into the ground and let you pick up more targets or smaller targets you could not notice with a lower threshold level as the numbers get lower and then into the negative numbers past 0 which actually raises the threshold for what you can notice into shallower depths.
Nothing gets covered up, you just add more signals to the mix which can make an already confusing wall of sound even more crowded and crazy but different combinations of thresh and gain levels can do some weird and sometimes wonderful things on these FTP products if you are able to do it with your detector and get used to seeing and noticing positive behavior patterns.
Check out the settings this guy is using in this vid...
Positive thresh, gain at 1...screwed up numbers but still hitting deep coins.



All I can say is this was all experimental for me in a nightmare iron infested site I was hunting but once I got the hang of noticing the non ferrous tones with no huge drops low and that range of numbers that repeated from more than one way I got better and better at cherry picking good targets in an ocean of iron.
It took time but once I did it got even easier as time went on to do it all the time at will.
I have done this with high gain and low thresh too but the higher Thresh levels just seem to make the non ferrous targets "pop" better.
Again, I don't know why, it just does.
Could be better ways to accomplish this but for me this always works and as I mentioned after years of doing it this way it is now second nature to me and my preferred way to hunt in iron.
I hunted with a buddy once and showed him my screen and let him listen to the tones as I moved my coil around an iron infested mineralized site we were hunting and he thought I was crazy, he couldn't pick out a good tone or any repeating behavior at all even if his life depended on it, but he knew I could because of the many targets I was finding and digging in areas he had just gone over with an E Trac and missed.
I tried to explain to him this method and what I looked for and exactly how I did this but he never got it.
It works on a Fisher but I doubt it would work on his E Trac so this was something that would have been useless to him, anyway.
Eventually I just said I could do it only because I stumbled on to this method and practiced doing it for many hours until I got good at it which was true.

Nasa Tom mentioned to me once in his forum that if I could do this with such hot settings and be successful that puts me in the top percentage range of detectorist out there.
Nice to hear but l believe it is really about how many hours I spent standing behind that F70 and learning it so well and using some good old observational skills.
I think anyone can learn to do it this way if they put in the effort and a few told me over the years they did that and it worked for them, also.
Then again others use other iron hunting methods and those work for them, too.
Just one more way to do something in this hobby...among many.
 
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