New detecting method?

[WM6]

Originally Posted by J_Player

What you say about ULF radar is very interesting. ULF has a very large wavelength (many km) which makes it hard to image any small object from interference/reflection in the way microwave radar can. But the ground penetration is excellent for very large things. If you wanted to use RF to detect things in the ground, then VLF would be more suitable because the wavelength is shorter to allow better resolution of the buried object. As you increase the frequency, the resolution improves but the ground penetration is less. So a treasure hunter is looking for a frequency between the low and high that will have good ground penetration to maybe 1 meter, and good resolution to be able to locate where the anomaly is.

We know geologists use frequencies usually between 10-30KHz to map large rock fractures and ore deposits as well as fault lines. But they cannot find a buried coin 10 cm deep. Their signals are long wavelength that detect up to 25m deep in the ground or more.

But if we raise the frequency to 100 KHz, then the wave becomes shorter and will only penetrate to maybe 10 meters deep. At 250KHz, we expect even less depth, but better resolution of shallow targets.

My question is what is the best frequency you would consider for as treasure hunter who only wants to see to 1-2 meters depth maximum?
From the charts I look at, it seems that this may be very close to the lower AM broadcast band of 550 KHz.

Do you think an AM radio or modified AM radio at below 550 KHz could be used for looking at LF/VLF interference under the ground?
Also, is there a way to use these frequencies as a VLF radar?

As you say in this field we can find a lot of question and research possibilities that can lead to one of (for amateur) rare ways to get something like real RDL (Reasonable Distance Locator). Principle are simple, realisation not so.

To reach long distances it is allways better to use lower frequencies, because as we go higher more dissipation on earth surface occured. This is not only reason to go at lower frequencies, we amateur are limited by our experimetation to rare authorized frequencies for such experiments or we are out of law. So, for us, relative safe are EM wave experiments inside upper spectrum of audio frequencies, say abuot 20kHz.

For "about 20 kHz" frequencies we need only weak transmitter to reach huge distance because of very low surface dissipation. On other side weak transmitter do not push our very weak tracked signals "back to underground" from our antenna and cover it and false its direction by its own signal strenght. Distance propagation of those wavelenght not mean that we can detect something at miles and kilometers, as babbling scammers propaganda. No, we can discuss only about meters, provided that we build our devices so, that it is possible. Nor detection of single coin from distance of a meter or so is impossible under some circumstances (at first of coin orientation against directed Rx antenna). But at first we can locate by this method different underground metalic deposits and not small golden nuggets.

Additional hint: such "about 20 kHz" weak transmitter equipped with well build and tunned stacked vertical antenna we can put even in our backyard and search in circle on radiated terrain kilometers away from home equipped only with a receiver. In this case transmitter have to be weak as discussed yet and well adjusted to antenna to prevent disturb our neighbors by radiated harmonic interferences.

In general VLF wave are not less reflective from the same target (if we neglect diffraction) as UHF wave but are more dispersive in reflection so we get by multiple factor weaker signal from VLF reflection as by same ULF propagation. Reason more for sensitive receiver and extremly directive Rx antenna.