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Volume of ground
- Thread starter Wirechief
- Start date
Hey Wirechief, I guess you mean can the TX induce a signal but the coil is too far away to RX
I had a similar thought but it's about how much signal is absorbed or filtered after the TX that keeps the target signal from a strong Rx.The reason is that it seems that a return signal would induce into other targets like hot rocks and give added ground noise before coming back to the coil. Wyndham
I had a similar thought but it's about how much signal is absorbed or filtered after the TX that keeps the target signal from a strong Rx.The reason is that it seems that a return signal would induce into other targets like hot rocks and give added ground noise before coming back to the coil. Wyndham
Hello Wyndam, what I was meaning is I wonder how much ground material is actually being analyzed by the uprocessor? I read somewhere that someone thinks the transmit signal turns laterally after about 3 feet. I don't know how they could tell that this is actually happening? Anyway I'm thinking upside down again I suppose! Well God Bless and just something to ponder on.
John Tomlinson,CET
John's Detectors
John Tomlinson,CET
John's Detectors
John,
A mono coil will analyze a volume of ground that is sort or cone shaped with the maximum depth in the middle. However, the characteristics of some soil will attenuate the response from what might be obtained in an air test.
DD coils have a somewhat wider response from the front to the back of the coil in the coil overlap region. They may not go as deep as a mono coil but their pickup pattern is a little wider and requires less coil sweep overlap for more complete ground volume coverage.
If a coil could have a perfect rectangular detection pattern below ground, you would be able to have a very efficient search pattern by pretending to paint the soil surface with a paint brush as wide as a search coil. However, since that is not the case some degree of overlap is required to ensure that deep targets are not missed. This does however, cause some overlap in covering shallower targets with some shallow below ground regions seeing more than one sweep of the coil.
As a beach hunter, I find that the 15" WOT DD coil (for the Sovereign XS2) gives me the best combination of sand volume coverage per sweep for the very reasons mentioned above. A slight overlap is all that is required to obtain good soil/sand volume coverage.
John, you are right to be thinking about total soil volume being analyzed, not just the surface area but what is below the ground too.
I hope this answers your question.
bbsailor
A mono coil will analyze a volume of ground that is sort or cone shaped with the maximum depth in the middle. However, the characteristics of some soil will attenuate the response from what might be obtained in an air test.
DD coils have a somewhat wider response from the front to the back of the coil in the coil overlap region. They may not go as deep as a mono coil but their pickup pattern is a little wider and requires less coil sweep overlap for more complete ground volume coverage.
If a coil could have a perfect rectangular detection pattern below ground, you would be able to have a very efficient search pattern by pretending to paint the soil surface with a paint brush as wide as a search coil. However, since that is not the case some degree of overlap is required to ensure that deep targets are not missed. This does however, cause some overlap in covering shallower targets with some shallow below ground regions seeing more than one sweep of the coil.
As a beach hunter, I find that the 15" WOT DD coil (for the Sovereign XS2) gives me the best combination of sand volume coverage per sweep for the very reasons mentioned above. A slight overlap is all that is required to obtain good soil/sand volume coverage.
John, you are right to be thinking about total soil volume being analyzed, not just the surface area but what is below the ground too.
I hope this answers your question.
bbsailor
Frank Hamill
New member
I did do this with several of my detectors and with my Goldquest SS...11" coil.
I took wooden rulers and drilled holes in a common place to all and made all the same lengths. I wanted to see just how wide, deep and the overall diameter of the radiated pattern was in each detector. If any nodes or peaks or holes were present in each. The picture is attached. If I remember correct I left each ruler 24 inches in length and used gold coins, gold rings, silver rings and coins to play with each detector.
The pattern of the Goldquest SS 11" coil is about like a balloon filled with 6 gallons of water.
Wish I was a more tect. person but I am not...but the visual description of a balloon with water in it works for me. FRank
I took wooden rulers and drilled holes in a common place to all and made all the same lengths. I wanted to see just how wide, deep and the overall diameter of the radiated pattern was in each detector. If any nodes or peaks or holes were present in each. The picture is attached. If I remember correct I left each ruler 24 inches in length and used gold coins, gold rings, silver rings and coins to play with each detector.
The pattern of the Goldquest SS 11" coil is about like a balloon filled with 6 gallons of water.
Wish I was a more tect. person but I am not...but the visual description of a balloon with water in it works for me. FRank
Frank Hamill
New member
I plotted the results from the air testing H and V into a computer program then colored the pattern. This colorizing got the size and shape of each detector radiated pattern firmly implanted in my mind while detecting in the field. FRank
Hello Wyndham and appreciate the response. I just start wondering about something and if you don't ask they can't say yes. I love the inner workings of these metal detectors. So I might be thinking in the wrong direction but I got to try Wyndham. Ok I hope you are well and CU later, God Bless.
John Tomlinson,CET
John's Detectors
John Tomlinson,CET
John's Detectors
Hi bb, thanks for your thoughts on this subject I apologize for being so long in responding. Eric and Wyndham have a good discussion going on measuring this I believe beneath ground surface. No telling what is being energized deeper down and we can't pick up the minute returning eddy currents due to limitations of present coils and amplifier circuits. It's amazing to me we do as well as we are with all of the emi and ground noises involved. Thanks bb!
John Tomlinson,CET
John's Detectors
John Tomlinson,CET
John's Detectors
Eric Foster
New member
Hi Wirechief and all,
Theoretical calculations are often based on a "infinite half space". In other words the maxtrix under the coil is assumed to be infinite in depth and breadth. That doesn't mean that the field extends that far, and in practical terms it would be unmeasurable after a few tens of feet laterally and vertically, except for huge coils. However, to illustrate the problem, in the sea using an underwater PI with a 10in coil, you can detect the approach of the bottom (or surface) by the reduction of sea water signal, when you are 30ft off the bottom, or approaching the surface. In between, the signal is constant. So, if you are in 90ft of water, the middle 30ft would give no change.
Eric.
Theoretical calculations are often based on a "infinite half space". In other words the maxtrix under the coil is assumed to be infinite in depth and breadth. That doesn't mean that the field extends that far, and in practical terms it would be unmeasurable after a few tens of feet laterally and vertically, except for huge coils. However, to illustrate the problem, in the sea using an underwater PI with a 10in coil, you can detect the approach of the bottom (or surface) by the reduction of sea water signal, when you are 30ft off the bottom, or approaching the surface. In between, the signal is constant. So, if you are in 90ft of water, the middle 30ft would give no change.
Eric.