Carl
I don't work for Mineoro. YES I know the two inventors. I assure you the both investigate long range detectors since many years and works all the days in this and they are serious persons. I was the person who said them the microcontroller version is not good, because the long distance detector REQUIRES external sensibility control, as old model DCH 85, you can see in a photo sent here (USA owner).
Now, via your message, I know your challenge.
I make semi-long distance detectors and contrast the PDC. The place where sounds my detector, sounds the PDC 205 or 210 and found the target.
I'm not scientific, but if I wait explanation from science WHY a simple RF detector in association with another electronics detects a coin (buried) 20 or more meters from the detector, never I will do experiments.
Why I involved in this? Because my first experience in metal detection was long distance, not the traditional, wich causes in me tremendous impression. As you, never I believe all this is possible.
The advantage of long range metal detector is the non-contact with the soil, mean don't have effects of mineralized soils and/or soil effect.
The more effective distance for a coin (80 m) with PDC 205 (in my particular experience) was in salty terrain. In another terrains decreases for a single coin. And this is a scientific fact (for me), because is a proof that the electrical conductivity of the soil increases much times this kind of non-contact with the soil detector system.
Ionic or electrical phenomenom, RF or what? Long range detector is an old reality. The photo in B&W of 1979 post now is another proof. Mr. John Baldwin (English, the more old man of all, died in 1987-88, don't remember very well) sustain a silver object found via electromagnetic-RF detector type radar. Mr. John and his different teams found thounsands gold and silver objects since 1960, first tube long range detectors, later transistorized as this photo.
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