I noticed that the other thread was closed so I could not respond there.
Here's an idea for what it's worth:
I have a PI detector as well as the Etrac. I use it in the water at the beach and in a fresh water sound near by.
It will sound off on ANY metal and I don't think mineralization effects PI detectors as much as VLF or FBS detectors.
Below is a snip from another site talking about how metal detector work: http://www.gi.alaska.edu/~jesse/treasure/misc/howdetector.html
"Discrimination
PI metal detectors are not capable of the same degree of discrimination as VLF metal detectors.
By increasing the time period between transmitter shut-off and the sampling point (pulse delay), certain metal items can be rejected. Aluminum foil will be the first to be rejected followed by nickel, pull tabs and gold. Some coins can be rejected at very long sample delays however, iron cannot be rejected.
There have been many attempts to design a PI that can reject iron however these attempts have had limited results. Iron is detectable at very long time delays however, silver and copper have similar characteristics. Such long time delays also have a negative affect on detection depth. Ground mineralization will cause some widening of the reflected pulse as well, changing the point at which a target responds or rejects. If the time delay is adjusted so that a gold ring doesn't respond in an air test, that same ring may respond in mineralized ground. Mineralized ground thus changes everything regarding the time delays and discrimination of PI metal detectors.
Ground Balance
Ground balancing, while very critical on VLF metal detectors, is not necessary with PI circuits. Average ground mineralization will not store any appreciable amount of energy from the search coil and will not usually produce a signal. Such ground will not mask the signal from a buried object. On the contrary, ground mineralization will add slightly to the duration of the reflected pulse increasing the depth of detection. The term "automatic ground balance" is often applied to PI instruments because it will normally not react to mineralization and there are no external adjustments for any specific ground conditions.
Heavy black sand is an exception. It will cause a VLF coil to overload, making metal detector penetration poor at best. A PI detector will work in black sand however, some false signals may result if the coil is held very close to the ground. Ground responses can be minimized by using a longer time delay between the shut-off and sample point (pulse delay). Advancing the time delay slightly will help to smooth out the noises caused by most mineralization. "
Perhaps you could borrow or buy a used PI detector and try those areas that have been "Hunted Out"
For the limited time I have used a PI detector I have discovered the following:
Loud screaming responses are either very large or very shallow targets.
Faint chirps are either very small or very deep targets.
If you use a PI detector that can get more depth and only chase those very faint signals, you may be able to pull up some of those old deep coins that nobody else can reach.
You may also go out of your mind if the area is littered with metal trash.
Just an idea.
Good luck.
Here's an idea for what it's worth:
I have a PI detector as well as the Etrac. I use it in the water at the beach and in a fresh water sound near by.
It will sound off on ANY metal and I don't think mineralization effects PI detectors as much as VLF or FBS detectors.
Below is a snip from another site talking about how metal detector work: http://www.gi.alaska.edu/~jesse/treasure/misc/howdetector.html
"Discrimination
PI metal detectors are not capable of the same degree of discrimination as VLF metal detectors.
By increasing the time period between transmitter shut-off and the sampling point (pulse delay), certain metal items can be rejected. Aluminum foil will be the first to be rejected followed by nickel, pull tabs and gold. Some coins can be rejected at very long sample delays however, iron cannot be rejected.
There have been many attempts to design a PI that can reject iron however these attempts have had limited results. Iron is detectable at very long time delays however, silver and copper have similar characteristics. Such long time delays also have a negative affect on detection depth. Ground mineralization will cause some widening of the reflected pulse as well, changing the point at which a target responds or rejects. If the time delay is adjusted so that a gold ring doesn't respond in an air test, that same ring may respond in mineralized ground. Mineralized ground thus changes everything regarding the time delays and discrimination of PI metal detectors.
Ground Balance
Ground balancing, while very critical on VLF metal detectors, is not necessary with PI circuits. Average ground mineralization will not store any appreciable amount of energy from the search coil and will not usually produce a signal. Such ground will not mask the signal from a buried object. On the contrary, ground mineralization will add slightly to the duration of the reflected pulse increasing the depth of detection. The term "automatic ground balance" is often applied to PI instruments because it will normally not react to mineralization and there are no external adjustments for any specific ground conditions.
Heavy black sand is an exception. It will cause a VLF coil to overload, making metal detector penetration poor at best. A PI detector will work in black sand however, some false signals may result if the coil is held very close to the ground. Ground responses can be minimized by using a longer time delay between the shut-off and sample point (pulse delay). Advancing the time delay slightly will help to smooth out the noises caused by most mineralization. "
Perhaps you could borrow or buy a used PI detector and try those areas that have been "Hunted Out"
For the limited time I have used a PI detector I have discovered the following:
Loud screaming responses are either very large or very shallow targets.
Faint chirps are either very small or very deep targets.
If you use a PI detector that can get more depth and only chase those very faint signals, you may be able to pull up some of those old deep coins that nobody else can reach.
You may also go out of your mind if the area is littered with metal trash.
Just an idea.
Good luck.