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Do PI detectors "air test" poorly??????
- Thread starter Ivan
- Start date
Yes and no..... You should turn the gain all the way up and then adjust the threshold to where its just barely warbling. The DF shines nicely in bad mineralization and wet sand. I also noticed my v3i and 12x15" coil getting about the same depth and overall better on faint small targets. The DF loves silver and aluminum cans. I am going to have to bury some coins and do a depth test. I have noticed best depth in damp sand and once disturbing the sand the signal would disappear, meaning the sand/soil matrix was conducting the signal. So yes air testing is around 2" less than what I find in damp sand on quarter size objects and 1.5" on dime sized. Silver screams no matter the condition. Small gold chains will be all but invisible, which sucks.
Rob in (Ca)
Active member
Air testing can be deceiving.......there's some VLF Detectors that will Air test a Quarter at 18 inch's .......But can not find a coin spill in the ground at 4 inch's ? ......
most PI's do not air test that good.....but will find targets deep deep in the salt sand, where VLF detectors can not perform.
When you do take your DF out to the beach, plan on doing a lot of deep digging
most PI's do not air test that good.....but will find targets deep deep in the salt sand, where VLF detectors can not perform.
When you do take your DF out to the beach, plan on doing a lot of deep digging
Hello ,
i support the idea that the test of a pi type machine give more depth in field test ...much much better than a air test contrary at Vlf...
Also in mineralised soil i will detect in my field test (target from .60 mt to 3 meters) better in Winter when the soil is dry than in summer when the soil is wet.
tested 100% many times.....
have a nice day
Alexis.
i support the idea that the test of a pi type machine give more depth in field test ...much much better than a air test contrary at Vlf...
Also in mineralised soil i will detect in my field test (target from .60 mt to 3 meters) better in Winter when the soil is dry than in summer when the soil is wet.
tested 100% many times.....
have a nice day
Alexis.
The whites DF is very deceiving when you use it ..air testing is a waste of time .Turn the Gain up to maximum... turn the threshold up till it is slightly audible(like our fellow members have suggested).And go to your nearest beach and do some testing and you will see the what we mean.It does take a few sessions to get familiar with it but really its very easy to use.My tip is dont swing too fast ,it picks up the tiny things like tiny paper staples.In the water it goes even deeper..Listen for very faint signals because they are the fun ones .You will be digging deep so get a large scoop. Have a nice day and enjoy your new detector
Hi Southwind,
I can give an idea of why a PI may not air test as well as a buried test and it is simple. PI's are really bad about reacting to external noise from about any source. Raise the coil in the air and that coil becomes a really great antenna. Lower that same coil close to the ground and the ground helps shield the coil from much of the noise. So, in the air, I may not get nearly the depth as I can if I bury the same object.
On just the right day I can air test up to 18" on a nickel with one of my PI's, but the next day I may be lucky to only obtain an air test of maybe 12". In the field, I used to bury a nickel at about 12" for a quick test just to verify the detector was working right. In almost all cases, the signal strength from that nickel was a strong response. I could easily bury the same coin deeper but that wasn't my main objective when I would run the test.
So, can one air test poorly but do much better on buried objects. The answer is yes. Can one display a poor test even on a buried test in one location and do a whole lot better somewhere else even though the ground may be very similar. Again, the answer is yes.
If the signal coming from the PI is crystal clear with no noise, then the detector should display the approximate same depth rather the object is buried or in an air test. Keep in mind the noise level doesn't have to sound that bad to make quite a difference.
One good way to check both a buried target and an air test is to use a noise canceling coil. Unfortunately, such coils generally lack depth compared to a similar mono of the same size. Because of the nature of a noise canceling coil, I normally use an elongated housing and build the figure 8 from front to back instead of side by side. My test coil I use at home is about 16" long by 5" wide. Inside I have a coil twisted into a figure 8 with each half close to half the length of the housing. This particular coil will display two distinct target responses, one in the front and one in the back, each having the approximate depth capability of maybe a 6" coil. What makes it nice is noise is no longer a problem, so it is easier to compare depths easier if I so desired.
Now, my reason for the noise canceling coil is to check my detector inside where noise could be a big problem and not for comparing different depth capabilities. Minimizing external noise problems allows one to concentrate other things besides trying to deal with trying to minimize noise sources.
I mention this noise canceling coil as a simple means of being able to do easier comparisons. Fortunately, building this type of coil is really quite easy to do.
Reg
I can give an idea of why a PI may not air test as well as a buried test and it is simple. PI's are really bad about reacting to external noise from about any source. Raise the coil in the air and that coil becomes a really great antenna. Lower that same coil close to the ground and the ground helps shield the coil from much of the noise. So, in the air, I may not get nearly the depth as I can if I bury the same object.
On just the right day I can air test up to 18" on a nickel with one of my PI's, but the next day I may be lucky to only obtain an air test of maybe 12". In the field, I used to bury a nickel at about 12" for a quick test just to verify the detector was working right. In almost all cases, the signal strength from that nickel was a strong response. I could easily bury the same coin deeper but that wasn't my main objective when I would run the test.
So, can one air test poorly but do much better on buried objects. The answer is yes. Can one display a poor test even on a buried test in one location and do a whole lot better somewhere else even though the ground may be very similar. Again, the answer is yes.
If the signal coming from the PI is crystal clear with no noise, then the detector should display the approximate same depth rather the object is buried or in an air test. Keep in mind the noise level doesn't have to sound that bad to make quite a difference.
One good way to check both a buried target and an air test is to use a noise canceling coil. Unfortunately, such coils generally lack depth compared to a similar mono of the same size. Because of the nature of a noise canceling coil, I normally use an elongated housing and build the figure 8 from front to back instead of side by side. My test coil I use at home is about 16" long by 5" wide. Inside I have a coil twisted into a figure 8 with each half close to half the length of the housing. This particular coil will display two distinct target responses, one in the front and one in the back, each having the approximate depth capability of maybe a 6" coil. What makes it nice is noise is no longer a problem, so it is easier to compare depths easier if I so desired.
Now, my reason for the noise canceling coil is to check my detector inside where noise could be a big problem and not for comparing different depth capabilities. Minimizing external noise problems allows one to concentrate other things besides trying to deal with trying to minimize noise sources.
I mention this noise canceling coil as a simple means of being able to do easier comparisons. Fortunately, building this type of coil is really quite easy to do.
Reg
Eric Foster
New member
Hi Reg and all,
I totally agree. There is no reason an air test should be worse than an "in ground" test, except for noise. When I do tests in my garden, which is in quite a noisy location, it is very noticeable that the noise diminishes as the coil is lowered toward the ground, even from 6 inches down to 1inch height. For an air test, always have the coil horizontal. Noise signals are polarized so that a vertical coil will always pick up far more noise than a horizontal one. For a realistic air test, lay the coil on a piece of 1in thick wood, MDF, or plastic on the ground surface, then wave a target over the top of the coil. The range obtained will not be measurably different to that if the target was buried. The above is true for PI detectors, but not necessarily so for induction balance types, where the operating frequency can make a very noticeable difference.
Eric.
I totally agree. There is no reason an air test should be worse than an "in ground" test, except for noise. When I do tests in my garden, which is in quite a noisy location, it is very noticeable that the noise diminishes as the coil is lowered toward the ground, even from 6 inches down to 1inch height. For an air test, always have the coil horizontal. Noise signals are polarized so that a vertical coil will always pick up far more noise than a horizontal one. For a realistic air test, lay the coil on a piece of 1in thick wood, MDF, or plastic on the ground surface, then wave a target over the top of the coil. The range obtained will not be measurably different to that if the target was buried. The above is true for PI detectors, but not necessarily so for induction balance types, where the operating frequency can make a very noticeable difference.
Eric.
Southwind,
You know a lot of manufacturing tech's who specialize in working on PI's? Interesting because I didn't know there were that many PI tech's anywhere.
There is a reason a large percentage of third party PI's were initially designed by Eric and that is he is probably the most knowledgeable person I know who shares technical information. So, I would guess he is quite knowledgeable on how PI's work and the tricks that can be used when checking them. Now, Eric has provided an interesting way of testing a PI that should make it easy to test variations in air tests for those wanting to try his ideas. You might try it and see what you come up with. I already have. Eric's discussion on keeping the coil horizontal versus vertical will quickly show just how dramatic noise can change as will raising a coil and lowering it to the ground.
Keep in mind my statement about why a PI can air test worse than an in the ground test strictly refers to PI detectors and not all detectors. VLF types are a different can of worms but even they have a tendency to display less noise as the coil is lowered to the ground. At least, they do where I have tested them and I have tested quite a few.
I also see you don't reference being a PI owner either. So, I have to assume your position on this noise issue is based upon your discussions with the metal manufacturer techs. Would you mind informing us of the PI tech's and having them contribute and offering their opinions. I am interested in why they feel the way you describe and if they have any secrets they are willing to share that I don't know about. I am always willing to learn.
Reg
You know a lot of manufacturing tech's who specialize in working on PI's? Interesting because I didn't know there were that many PI tech's anywhere.
There is a reason a large percentage of third party PI's were initially designed by Eric and that is he is probably the most knowledgeable person I know who shares technical information. So, I would guess he is quite knowledgeable on how PI's work and the tricks that can be used when checking them. Now, Eric has provided an interesting way of testing a PI that should make it easy to test variations in air tests for those wanting to try his ideas. You might try it and see what you come up with. I already have. Eric's discussion on keeping the coil horizontal versus vertical will quickly show just how dramatic noise can change as will raising a coil and lowering it to the ground.
Keep in mind my statement about why a PI can air test worse than an in the ground test strictly refers to PI detectors and not all detectors. VLF types are a different can of worms but even they have a tendency to display less noise as the coil is lowered to the ground. At least, they do where I have tested them and I have tested quite a few.
I also see you don't reference being a PI owner either. So, I have to assume your position on this noise issue is based upon your discussions with the metal manufacturer techs. Would you mind informing us of the PI tech's and having them contribute and offering their opinions. I am interested in why they feel the way you describe and if they have any secrets they are willing to share that I don't know about. I am always willing to learn.
Reg
I need to learn it more than I do now. I also use a Sovereign GT, and an Explorer SE Pro2. Each machine has different idiosyncrasies. 
W6pea,
The ML SD 2200 series is extremely sensitive to external noise. At least, my SD 2200 D version is. Try to do an air test with the SD in the odds are one will find a very dramatic difference between the air and in ground test even in quiet areas. This is mainly due to the extreme sensitivity as set by the design, thus making the detector very susceptible to noise when compared to most other PI's. As an example, it is about impossible for me to get any accurate air test within most city limits on my SD, but I can get much closer between an air test and an in the ground test on my TDI, the GS 5 and some of my other PI's.
My testing in town at my house or nearby indicates the TDI is far more sensitive than my SD on about any air test plus my buried 1 gram nugget test. Move the testing away from all noise sources and that clearly isn't the case. Typical air tests, at least on my SD are even difficult to do in areas that appear to be relatively free of noise. In fact, my SD will warble and indicate excessive noise in areas that show almost no noise on my TDI. Again, the reason is the fact the SD gain is so much higher than that on the TDI.
This is something to keep in mind when testing the SD and why I don't worry about air testing results on any PI, especially a ML.
The ML SD 2200 series is extremely sensitive to external noise. At least, my SD 2200 D version is. Try to do an air test with the SD in the odds are one will find a very dramatic difference between the air and in ground test even in quiet areas. This is mainly due to the extreme sensitivity as set by the design, thus making the detector very susceptible to noise when compared to most other PI's. As an example, it is about impossible for me to get any accurate air test within most city limits on my SD, but I can get much closer between an air test and an in the ground test on my TDI, the GS 5 and some of my other PI's.
My testing in town at my house or nearby indicates the TDI is far more sensitive than my SD on about any air test plus my buried 1 gram nugget test. Move the testing away from all noise sources and that clearly isn't the case. Typical air tests, at least on my SD are even difficult to do in areas that appear to be relatively free of noise. In fact, my SD will warble and indicate excessive noise in areas that show almost no noise on my TDI. Again, the reason is the fact the SD gain is so much higher than that on the TDI.
This is something to keep in mind when testing the SD and why I don't worry about air testing results on any PI, especially a ML.
Hi,
I recently got a Minelab GPX 5000 & have only tested it indoors.
I have found it to be very noisy even while placing the coil horizontal & turning off all electrical devices & reducing rx gain the only way i can make it quiet is by moving the coil switch into cancel & then it hardly detects coins unless they are very close to the coil.
Is this normal & also the volume seems quiet when i do manage to detect say a coin is this normal or does anyone think i may have a defective detector/coil?
I have been using the 11" Double D coil.
Thanks for any help.
I recently got a Minelab GPX 5000 & have only tested it indoors.
I have found it to be very noisy even while placing the coil horizontal & turning off all electrical devices & reducing rx gain the only way i can make it quiet is by moving the coil switch into cancel & then it hardly detects coins unless they are very close to the coil.
Is this normal & also the volume seems quiet when i do manage to detect say a coin is this normal or does anyone think i may have a defective detector/coil?
I have been using the 11" Double D coil.
Thanks for any help.
Reg;
Thank you for your reply. I have to agree "The ML SD 2200 series is extremely sensitive to external noise. At least, my SD 2200 D version is." Almost exactly to the word......SD2200v2, testing at home in the city, out in the desert 5 miles this side of &%#$ completely different story.
Thank you for your reply. I have to agree "The ML SD 2200 series is extremely sensitive to external noise. At least, my SD 2200 D version is." Almost exactly to the word......SD2200v2, testing at home in the city, out in the desert 5 miles this side of &%#$ completely different story.
Garrett was the only manufacturer I can remember that offered underwater weighted coils with 50 feet of cable. I saw these for the VLF Deepseeker range and the Groundhogs, they even had them for their discriminating B.F.O. machine. 12" coil would only detect fist sized and above targets. For coins there was a five inch.
Don't think they offered this type of coil for later machines but I can't see why it shouldn't work.
Don't think they offered this type of coil for later machines but I can't see why it shouldn't work.
vlad
Well-known member
the receive sensitivity, the transmit sensitivity, or both. If its the receive sensitivity then its going to be more prone to "emi." Plus you
have at a certain point an inherent amount of circuit noise you will start to hear and 60 cycle interference is strongest around 15 kHz..
If you have a transmit sensitivity you can simply turn it up and overpower the "emi" that has been creating the noise you are hearing. It also makes the carrier signal more powerful, and I've yet to hear anyone complain about practical power as opposed to a power level
that cannot be used.
The other thing I would mention is how well made is the loop and how efficiently can the "Q" of the loop be filled, depending on the design. The more highly resonance matched the tx winding and rx winding the more the noise reduction (up to 10X), to include extraneous signals not in phase with the carrier signal, the less power needed, less signal amplification in the rx section, better and more reliable discrimination [depending on method], and the more sensitive the detector.
I have experienced less noise with the loop parallel to the ground instead of holding it up to do air tests. And I've experienced more depth in the ground, but that may have been that I was able to hear the threshold speed up, and was not able to tune the detector as precisely and hear the changes in air tests. And there is the issue of the metallic oxide forming around the object in the ground; does this enhance the size of the target the detector sees?
have at a certain point an inherent amount of circuit noise you will start to hear and 60 cycle interference is strongest around 15 kHz..
If you have a transmit sensitivity you can simply turn it up and overpower the "emi" that has been creating the noise you are hearing. It also makes the carrier signal more powerful, and I've yet to hear anyone complain about practical power as opposed to a power level
that cannot be used.
The other thing I would mention is how well made is the loop and how efficiently can the "Q" of the loop be filled, depending on the design. The more highly resonance matched the tx winding and rx winding the more the noise reduction (up to 10X), to include extraneous signals not in phase with the carrier signal, the less power needed, less signal amplification in the rx section, better and more reliable discrimination [depending on method], and the more sensitive the detector.
I have experienced less noise with the loop parallel to the ground instead of holding it up to do air tests. And I've experienced more depth in the ground, but that may have been that I was able to hear the threshold speed up, and was not able to tune the detector as precisely and hear the changes in air tests. And there is the issue of the metallic oxide forming around the object in the ground; does this enhance the size of the target the detector sees?
TheDualFieldBandit
New member
I've got the dual field read all of cjc books on it. So I've done alot of bench testing with it before reading Eric's post on the coil position. I took it one step further as to find clean ground bash my heel into the ground to make a dent for the coil lug. Now I have it upside down laying flat on the ground with bottom of the coil pointing up. In my previous test I used a three gram and a six gram 14k bands. The three gram best test was (ten inches) and the six gram (twelve inches). With the coil laying flat on the ground described as above the test improved because I could hear better with less EMI The three gram (twelve inches) and the six gram (fourteen inches) all test were pushing it but repeatable signals. The DF controls were (1)gain at 9 O'clock (2)delay off 6 O'clock (3) threshold 11 O'clock best threshold smooth and steady! I live eight hundred feet above sea level and I notice that here it seems to have more EMI than when I get down to around sea level? I also notice this dual field seems to really come to life once it goes into the saltwater dug things much deeper than my bench tests??? In cjc books describes on how to tell different items from one another? Not so sure on this one the best I've so far been able to do is size a object up and how far it maybe from the coil plus tell the differences in some of the responses in the tone from say items like...Iron (rough tone in the signal) rusted bottle cap (rougher/crackle tone in the signal) US nickel (clean tone but with a slight roughness) aluminum (cleaner tone in signal with the slightest hint of a rasp) gold (the cleanest tone to the signal smooth through out) These things is just what I've noticed with the dual field. Now the disclaimer I'm not an expert nor do I know a fraction of what Eric or CJC knows! but I'm trying to learn!!! Thanks hope this was helpful....Ozz