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Originally Posted by aft_72005
Without reply !!!!!!????
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Maybe LRL experts do not know what the differences are. ?
From the perspective of a person who understands metal detector theory and LRL theories, I can explain what appears to be the diffrerence in theories and maybe operation between LRLs and metal detectors. Maybe an LRL expert who knows the answers can find some errors in my perspective and explain how it really works.
To begin, there are many kinds of LRLs:
A. Dowsing and electronically enhanced dowsing types.
B. Active coil types that broadcast an alternating signal that may be detected by any number of means.
C. Passive electronic types that listen for signals similar to a radio receiver with no transmitter.
D. Hybrid types that use a modified metal detector of some sort combined with "strange" circuitry that is not well explained.
There are many variations of these kinds of LRLs with overlapping between the classifications.
Variations can include using any of the following TX and RX methods:
1. Coils tuned to ELF, VLF and any other RF frequency into the microwave region (most often VLF).
2. Ariel antennas operating at anywhere between ELF to microwave.
3. LEDs, Lasers for TX of a beam to stimulate different areas of ground to be scanned, and coils to detect the response from the ground.
4. Broadcast band receivers used in passive mode or in conjunction with low power transmitters.
5. Electrostatic electronic sensors.
6. Dowsing rods with electronics added, such as low power signal generators connected to the rods or to the ground, or broadcasting in the air.
7. Dowsing rods with samples, magnets or "power loads" added to somehow influence the effectiveness of the rods.
Of all the kinds of LRLs I listed, the most similar to a metal detector is the TX/RX coil style pistol detector.
What is different?
Metal detector theory
Metal detector theory requires the TX coil to produce eddy currents in a target metal that can be detected in a receiver circuit. This depends on using a sensitive circuit and coil that can pick up the eddy currents, and hopefully examine the kind of eddy current to help determine what kind of metal is detected. Metal detectors are limited by the range of the magnetic field that can be transmitted as well as the range of the magnetic field of eddy currents. When the RX circuits are turned up to a high enough gain for maximum range, the problem becomes electronic noise from the internal circuits. If the circuits are optimized for minimal noise, then the second problem of external noise will become prominent --- noise from power lines, EMI, RF in the air, and even noises from the ground due to variations in earth currents interacting with mineralization in the soil. In order to avoid this kind of interference, most detectors have a faraday shield and ground balance circuits to "de-sensitize" the electronics so it will find signals that are not buried in the noise. The remaining signal is focused on the magnetic field with the electric field removed.
PD theory
If we compare a simple TX/RX coil type PD LRL to a metal detector, the first difference is there is no Faraday shield. The PD is also equipped with adjustments that allow it to be tuned much deeper into the noise region, and in some cases beyond stable circuit operation. We hear the experts of LRLs tell how it is necessary to move very slowly and hold the PD steady out in front pointed below the horizon, as well as not to wear clothing that collects static. It would seem they are trying to detect a signal at the extreme sensitivity adjustment, where any user movements could cause false signals. In fact, I expect this sort of detection to pick up a lot of EMI/RF and other interference noise from the air. The signals they are looking to find are not eddy current signals. For a VLF coil to receive a signal more than a meter or so, it must be operating as a radio receiver looking for variations in the broadcast signal. Without a Faraday shield, the electric field is not inhibited, so full RF TX and RX are possible. Possibly the amount of RF that is absorbed in the soil changes, and the diffraction of RF can be sensed. Or maybe there are RF reflections when a target is in range. According to some of the LRL experimenters, there is a hot spot in the location of long time buried metals that interacts with the signal they receive. It is unclear whether this signal must be transmitted, or if it exists separately from a transmitter, and can be detected with a simple passive receiver.
So far I described the theoretical difference between only one kind of LRL and a metal detector. There are many other kinds of LRLs.
The common difference LRLs all have from a metal detector can be summarized as follows:
1. They are claimed to detect metals at long distance using methods that cannot be demonstrated to be working live in front of skeptical witnesses.
2. Most LRLs require long-time buried metals in order to work. LRL experts claim they detect a secondary phenomenon that develops after metal has been buried a long time. But what secondary phenomenon they claim to detect has never been explained in a manner that can be demonstrated or duplicated. Usually the method of operation claimed can be shown to be untrue with simple instruments.
3. Anyone with electronics and construction skills can build a metal detector that works. Nobody can build an LRL that works except a very few people who do not demonstrate the LRL working in front of skeptical witnesses*. The idea that their LRL works exists only in their stories, not in the experience of most people who read their stories.
4. All LRLs seem to require special methods or skills to use them successfully. From dowsing to electronic coil LRLs, there are special instructions that must be followed before any chance of detecting can happen. Also the "environmental conditions" must be favourable in order for them to work. These requirements seem to work to compliment the fact that LRLs cannot be demonstrated in front of skeptical witnesses. These requirements also work to compliment the fact that nobody can build an LRL except the very few people who say they can, but do not demonstrate them working.
Those are some differences between metal detectors and LRLs that I have observed from a technical perspective.
Are there any LRL builders or users that see some errors in my observations, or know some more differences?
Best wishes,
J_P
* Exception: Morgan and Geo demonstrated LRLs they built to other forum member (not completely skeptical). Maybe there are a few others who also did?