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Calling on the experts here. Sensitivity control vs. depth performance?:nerd:
- Thread starter utmike
- Start date
Mike, I'm certainly no expert, but my experience tells me that although you may get an increase in depth by increasing your sensitivity on the detector, the increases are not directly proportional. The amount of increase may vary, depending on the mineralization of the soil. Where I am and mainly detect, most of the soil is not too badly mineralised, and using sensitivity of say, 10/30 on my XT 70, I can expect depth of 4" to 5" without any problems on small to medium sized coins. Increasing the sensitivity to say, 20/30 I would be surprised if depth of detection increased by more than 2" to 3" (giving new depth of 6" to 8" on those same coins. These figures may not be totally accurate as I haven't carried out definitive tests, but am going on my memory of my own experiences. Hope this helps, Sapper.
I'm no expert, but been into this since the early 70's... Sensitivity is not really a depth control.. After testing my 70 you don't gain much depth (if any) past 26.. Same with my other detectors.. What you will gain is "sensitivity" the ability to find smaller objects (earing backs for example)..
Ray..
Ray..
Most/many of the models offered today in the last number of years have a Sensitivity or Gain control that is really associated with the receive signal, not the transmit signal/energy. Part of what you asked is the following:
A control that is primarily in harmony with the return signal would have to do with the receive signal. If you have an X-Terra model (or other make/model) try this. With the detector turned ON and set to the highest Sensitivity/Gain setting, select the all metal Pinpoint mode. Use a small coil to determine the greatest distance from the coil you get a signal. Now, without making any other changes, reduce the Sensitivity to a half-way setting and then a minimum setting and check that distance again in the All Metal Pinpoint mode.
If the coil-to-coin distance remains the same or shows very minimal change, then the Sensitivity/Gain control is associated principally with the receive signal. Thus, you now answer that part of your question. The rest gets more difficult.
Some makes/models provide one or more control adjustments that are tied together for adjusting the performance/response of the motion discriminate signal. For example, with most Tesoro models the Sensitivity control is principally an adjustment for the Discriminate mode (motion) receive signal. However, the variable Threshold control can also effect the result in the Discriminate mode. Since I started using and selling Tesoro's in the early '80s I would occasionally use and teach what I called "Hyper-Tune". In more recent years Tesoro has called it "Super-Tuning" and it is accomplished by adjusting the Threshold control to or almost to a maximum setting. While it makes the All Metal mode useless, it adds to a full volume response from weaker (smaller and/or deeper) targets.
What this is doing is saturating the audio compared with having a more modulated audio (one that gives a stronger response to shallower targets and less audio as the coil-to-target distance increases). My White's XL Pro has a factory-set full Sensitivity level, but provides a variable control called Signal Balance that is an adjustment for the return signal. It is the same function as that on the XLT called Pre-Amp Gain. Adjusting the received signal's gain/sensitivity before (pre-amp) the amplification circuitry. The XLT, like the DFX and new Vision/Spectra V3, also have seperate adjustments for the All Metal mode Sensitivity and Discriminate mode sensitivity.
Minelab's Explorer provides adjustments, too, that can adjust the received signal in various ways. I'll apologize for rambling but that's what happens at 1:51 AM perhaps.
Other variable enter in when trying to determine the amount of depth achieved or lost with Sensitivity settings, such as search coil size and type, ground mineralization, sweep speed/coil presentation, etc.
Then easiest way for me to answer some of your questions for myself with any particular model regardless of the site I am at is this. I will use the best coil for the task, such as a smaller coil when working trashier sites, larger/standard coil for more open sites with fewer targets to cause target masking. Once I feel I have the right coil choice, I set the Threshold and Ground balance for peak performance and use the highest Sensitivity setting I possibly can. I like to operate "at the edge" of instability, as a rule. If I run with too much sensitivity there will be too much 'noise' and I won't be able to distinguish a noisy chatter audio from a slight target response. If I am 'at the edge' then I know I am getting all the depth I can w/o noise with that particular model.
At that point I am not too concerned about what I might be missing with the model in hand, just that I am doing the best I can with it. The, at that site. with that model and coil selection, I might reduce the Sensitivity/Gain a little on some questionable targets just to determine how much I can reduce it without giving up the performance I want.
I know this isn't the definitive answer you were hoping for, but not having an X-Terra on hand right now I can't take the time to figure some of it out for you.
PS: I hope your weather's good this weekend. I know I wish I was in Utah today as one of my sons has pulled some Barber's out of his Mayor's yard and has permission to work it and some other private sites some more.
He's not that proficient with any detector like two of my other sons are so I know I'd get more than my share. 
Monte
utmike said:
A control that is primarily in harmony with the return signal would have to do with the receive signal. If you have an X-Terra model (or other make/model) try this. With the detector turned ON and set to the highest Sensitivity/Gain setting, select the all metal Pinpoint mode. Use a small coil to determine the greatest distance from the coil you get a signal. Now, without making any other changes, reduce the Sensitivity to a half-way setting and then a minimum setting and check that distance again in the All Metal Pinpoint mode.
If the coil-to-coin distance remains the same or shows very minimal change, then the Sensitivity/Gain control is associated principally with the receive signal. Thus, you now answer that part of your question. The rest gets more difficult.
Some makes/models provide one or more control adjustments that are tied together for adjusting the performance/response of the motion discriminate signal. For example, with most Tesoro models the Sensitivity control is principally an adjustment for the Discriminate mode (motion) receive signal. However, the variable Threshold control can also effect the result in the Discriminate mode. Since I started using and selling Tesoro's in the early '80s I would occasionally use and teach what I called "Hyper-Tune". In more recent years Tesoro has called it "Super-Tuning" and it is accomplished by adjusting the Threshold control to or almost to a maximum setting. While it makes the All Metal mode useless, it adds to a full volume response from weaker (smaller and/or deeper) targets.
What this is doing is saturating the audio compared with having a more modulated audio (one that gives a stronger response to shallower targets and less audio as the coil-to-target distance increases). My White's XL Pro has a factory-set full Sensitivity level, but provides a variable control called Signal Balance that is an adjustment for the return signal. It is the same function as that on the XLT called Pre-Amp Gain. Adjusting the received signal's gain/sensitivity before (pre-amp) the amplification circuitry. The XLT, like the DFX and new Vision/Spectra V3, also have seperate adjustments for the All Metal mode Sensitivity and Discriminate mode sensitivity.
Minelab's Explorer provides adjustments, too, that can adjust the received signal in various ways. I'll apologize for rambling but that's what happens at 1:51 AM perhaps.
Other variable enter in when trying to determine the amount of depth achieved or lost with Sensitivity settings, such as search coil size and type, ground mineralization, sweep speed/coil presentation, etc. Then easiest way for me to answer some of your questions for myself with any particular model regardless of the site I am at is this. I will use the best coil for the task, such as a smaller coil when working trashier sites, larger/standard coil for more open sites with fewer targets to cause target masking. Once I feel I have the right coil choice, I set the Threshold and Ground balance for peak performance and use the highest Sensitivity setting I possibly can. I like to operate "at the edge" of instability, as a rule. If I run with too much sensitivity there will be too much 'noise' and I won't be able to distinguish a noisy chatter audio from a slight target response. If I am 'at the edge' then I know I am getting all the depth I can w/o noise with that particular model.
At that point I am not too concerned about what I might be missing with the model in hand, just that I am doing the best I can with it. The, at that site. with that model and coil selection, I might reduce the Sensitivity/Gain a little on some questionable targets just to determine how much I can reduce it without giving up the performance I want.
I know this isn't the definitive answer you were hoping for, but not having an X-Terra on hand right now I can't take the time to figure some of it out for you.
PS: I hope your weather's good this weekend. I know I wish I was in Utah today as one of my sons has pulled some Barber's out of his Mayor's yard and has permission to work it and some other private sites some more.
He's not that proficient with any detector like two of my other sons are so I know I'd get more than my share. Monte
BarnacleBill
New member
For in field practical use this is a difficult question to quantify. There are three general sources of noise to contend with that can cause instability.
1. External; EMI, power lines, data lines, RF, other detectors etc etc
2. Internal noise, this is noise created by the electronics in the detector itself.
3. Ground noise, the minerals in the ground.
On an X-Terra I would not use the Pinpoint method mentioned by Monte for several reasons which are unique to the X-Terra's. That method may be fine with certain other detectors, but the X-Terra's are a different animal. And the reasons why:
X70, X50, X30, X305, X505
1. The sensitivity levels are programmed independently in software for each of the different functions. And though they may be ganged to the sensitivity menu setting adjusted by the end user, there is no guarantee of equivalency.
2. The above is further complicated by the fact that the Pinpoint mode uses an Automatic Gain circuit, which over time will continue to ramp up gain until it finds a signal. Then it will immediately attenuate the signal once it finds one. Therefore the sensitivity is constantly shifting in Pinpoint with no stable setting to use as a reference point.
X705
The X705 via it's sizing mode eliminates the major issue of point #2 above. But there is no guarantee that the sensitivity level in C & T motion mode is the same as Pinpoint mode, nor that the slope of the gain is the same etc etc.
The long & short is that each coil in each type of ground has to be tested. I believe that the following statement would be accepted by most, "the larger the coil the deeper it will find targets". That sounds like a perfectly reasonable statement, and one sees all sorts of posts on forums on how you can't detect deeper than the diameter of the coil etc etc. Sounds good, completely wrong of course.
If you read the following post I made, especially the Saltwater section at the bottom, it should provide food for thought. Though I did not directly test to your question of varying sensitivity with the same coil, it may provide you with a basis to do your own testing.
http://www.findmall.com/read.php?55,571137,571137#msg-571137
But I would like to provide you with a little more information in regards to pushing the sensitivity. Having tested several X70's & the X705 in mild white freshwater beach sand, I consistently find that 28 is about the limit to keep the detector perfectly quiet in All Metal C & T mode. A setting of 29 starts to spit a little(10%of the time), and 30(25% of the time). And the previous behavior is pretty consistent using a variety of coils. However, and this is where I may get some flack
, the X30, X50, X305, X505 can be run at full sensitivity with no spitting over the same ground. They are therefore less sensitive than the 70-700 class detectors.
But let me say this about that.
If you are primarily going to be hunting trashy areas like parks etc., then you are most likely going to use common sense and turn down the sensitivity along with employ a small coil. In these types of areas you will be able to run higher on the sensitivity on the X30, X50, X305, X505 than on the X70/X705. But you should arrive at an sensitivity equivalency across these classes of detectors. And might I say that this is where the X305 with the small HF DD is going to mop the floor with a lot of detectors. What a killer park setup!
HH
BarnacleBill
1. External; EMI, power lines, data lines, RF, other detectors etc etc
2. Internal noise, this is noise created by the electronics in the detector itself.
3. Ground noise, the minerals in the ground.
On an X-Terra I would not use the Pinpoint method mentioned by Monte for several reasons which are unique to the X-Terra's. That method may be fine with certain other detectors, but the X-Terra's are a different animal. And the reasons why:
X70, X50, X30, X305, X505
1. The sensitivity levels are programmed independently in software for each of the different functions. And though they may be ganged to the sensitivity menu setting adjusted by the end user, there is no guarantee of equivalency.
2. The above is further complicated by the fact that the Pinpoint mode uses an Automatic Gain circuit, which over time will continue to ramp up gain until it finds a signal. Then it will immediately attenuate the signal once it finds one. Therefore the sensitivity is constantly shifting in Pinpoint with no stable setting to use as a reference point.
X705
The X705 via it's sizing mode eliminates the major issue of point #2 above. But there is no guarantee that the sensitivity level in C & T motion mode is the same as Pinpoint mode, nor that the slope of the gain is the same etc etc.
The long & short is that each coil in each type of ground has to be tested. I believe that the following statement would be accepted by most, "the larger the coil the deeper it will find targets". That sounds like a perfectly reasonable statement, and one sees all sorts of posts on forums on how you can't detect deeper than the diameter of the coil etc etc. Sounds good, completely wrong of course.
If you read the following post I made, especially the Saltwater section at the bottom, it should provide food for thought. Though I did not directly test to your question of varying sensitivity with the same coil, it may provide you with a basis to do your own testing.
http://www.findmall.com/read.php?55,571137,571137#msg-571137
But I would like to provide you with a little more information in regards to pushing the sensitivity. Having tested several X70's & the X705 in mild white freshwater beach sand, I consistently find that 28 is about the limit to keep the detector perfectly quiet in All Metal C & T mode. A setting of 29 starts to spit a little(10%of the time), and 30(25% of the time). And the previous behavior is pretty consistent using a variety of coils. However, and this is where I may get some flack
, the X30, X50, X305, X505 can be run at full sensitivity with no spitting over the same ground. They are therefore less sensitive than the 70-700 class detectors.But let me say this about that.
If you are primarily going to be hunting trashy areas like parks etc., then you are most likely going to use common sense and turn down the sensitivity along with employ a small coil. In these types of areas you will be able to run higher on the sensitivity on the X30, X50, X305, X505 than on the X70/X705. But you should arrive at an sensitivity equivalency across these classes of detectors. And might I say that this is where the X305 with the small HF DD is going to mop the floor with a lot of detectors. What a killer park setup!HH
BarnacleBill
And all units differ and some well thought out posts to follow..Basically the idea is to set it high enough keeping a stable unit and having used many units usually a 6-7 out of 10 is probably Max. and if you run it higher in extremely good ground very little useable depth increase. Certainly not proportional from 1 to 10 and you can also throw out the statements such as if a 8 inch coil goes 8 inches a 10 inch will go 10 inches. I really feel the knowlegable posts preceding mine covered it well...
utmike
Well-known member
Let me say that my question is based on an experience that still keeps me awake at night Last year, we hunted an old park with a couple of seasoned pros. I was told to watch one guy in particular ( with an explorer ) and when he threw his trowel into the ground and made it stick, it was time to gather round for a lesson in metal detecting 101.
Well, after a while he did just that and before he dug the target, he had us all run our detectors over his target. The two pros got nice repeatable signals and both agreed that the target was a deep token. My wife checked it with her Teknetics and got a broken/jumpy signal. My terra with the stock coil didn't get much more than a faint click of audio and a brief flash on the TID ( I don't remember the number ). My wife and I agreed that we would have pretty much ignored this one and kept hunting.
The target was a rare token 8"+ under a tree root. This got into my head so bad that I went to the other side of the park and looked for the worst signals possible. I ended up digging a war nickel that registered all over the place. To this day, I am convinced that with the right coil and tuning set-up, I could have read that token better.
Now, a year later I have learned a thing or two and am into some better finds (and have a much better arsenal of coils). I know I still have a LOT to learn and that won't be my last humbling experience. It's that one that is just out of range that has me going nuts!!!
I admit, I've thought about getting the Explorer or or Etrac for the added punch but, I love my X70 for its ease, lightweight and versatility not to mention I have a lot of $$$ invested into it.
(BTW Monte, the weather in Utah is great right now! Tell your son if he gets bored with those Barbers, we'd be happy to step in!!
)
Thanks again for all the VERY helpful info.
Mike
Last year, we hunted an old park with a couple of seasoned pros. I was told to watch one guy in particular ( with an explorer ) and when he threw his trowel into the ground and made it stick, it was time to gather round for a lesson in metal detecting 101.Well, after a while he did just that and before he dug the target, he had us all run our detectors over his target. The two pros got nice repeatable signals and both agreed that the target was a deep token. My wife checked it with her Teknetics and got a broken/jumpy signal. My terra with the stock coil didn't get much more than a faint click of audio and a brief flash on the TID ( I don't remember the number ). My wife and I agreed that we would have pretty much ignored this one and kept hunting.
The target was a rare token 8"+ under a tree root. This got into my head so bad that I went to the other side of the park and looked for the worst signals possible. I ended up digging a war nickel that registered all over the place. To this day, I am convinced that with the right coil and tuning set-up, I could have read that token better.
Now, a year later I have learned a thing or two and am into some better finds (and have a much better arsenal of coils). I know I still have a LOT to learn and that won't be my last humbling experience. It's that one that is just out of range that has me going nuts!!!
I admit, I've thought about getting the Explorer or or Etrac for the added punch but, I love my X70 for its ease, lightweight and versatility not to mention I have a lot of $$$ invested into it.(BTW Monte, the weather in Utah is great right now! Tell your son if he gets bored with those Barbers, we'd be happy to step in!!
)Thanks again for all the VERY helpful info.
Mike
on normal old home sites I start off with a sensitivty of about 23-24, and if I have no trouble I may bump it to 25, now if I get a real questionable deep whisper, I will check it in all directions and sometimes bump the sensitivity up to 26-27 and check the target again. Normally if a real deep target remains in all positive numbers I will dig it no matter what number the detector is giving me. I have never had a real deep 8+inch coin give me a good repeatable signal, seems they always bounce around when they are that deep. But I feel I definately can get more depth when I am on sites where I can quietly run sensitivity at 25-26.
I never ever run sensitivity lower than 22, maybe the soil in my area is just decent I don't know but at times when I tried to run lower than 22 I just did not get the depth I wanted to get the deep targets. I think 23-24 is the minimum for my area, you just have to experiment when you get to each site and see what works best for you
I never ever run sensitivity lower than 22, maybe the soil in my area is just decent I don't know but at times when I tried to run lower than 22 I just did not get the depth I wanted to get the deep targets. I think 23-24 is the minimum for my area, you just have to experiment when you get to each site and see what works best for you