Quote:
Originally Posted by goldfinder
JP and Fred - you are very funny guys. 
As to metal box vs wood. In my experiments with this my reasoning was that measuring the changes in the local electrostatic field was my goal at that time. So having a ground plane with the antenna pointing out from it, but not connected, gave me a way to see relative E-field differences. The wood box afforded no protection within the circuit so the local ES field was not really measurable as there was no fixed relation between ground and ES antenna charge detection.
What I really discovered in the field is ES is a poor way to look for treasure. I was able to show that ES fields are everywhere. All the bushes have ES field. So do the trees. Every step i took elicited ES response as the rubbing of grains of sand by my stepping on them generated sufficient response in the ES detector. And on and on.
Then I went to detection of ions (a new circuit). The sand thing still bothered this type of detector.
So telling me Mine Oro boxes used this type of box or that is really nonsense. 
I did learn a lot about ES detection. Not sure if that was a plus.
If someone was to ask me (which is unlikely) what is the best possibility for passive LRL I'd likely answer magnetic anomalies. The reason - gold is mildly anti-magnetic. Any large concentration of gold should produce a measurable magnetic difference to the local magnetic field. If someone would like to supply me with a couple of hundred ounces of gold so I can test this theory I would be electrostatic er ecstatic. 
Goldfinder |
Hi goldfinder,
You are correct for electrostatic anomaly detection.
The best of electrostatic field detectors always use a metal box to provide a ground near the antenna, so the antenna will not become charged to the relative field in the air around it. the metal box also acts as a shield for the front end high impedance circuits inside. The concept of ground plane is more appropriate for radio antennas, not electrostatic antennas. But there is a similar principle at work for electrostatic field detection.
In order to understand the dynamics of detecting electrostatic fields, you must first have some basic understanding about what fields exist in the natural environment where you are detecting. As you said, trees and other plants have a detectable field, as well as any animals roaming across the ground. This is because they are electrically connected to the ground, and will conduct the ground potential up through their body. Even leaves from the top of a tall tree will have 0v charge instead of 2000-3000 volts charge that you will find at that altitude where there is no tree in the air.
In addition to understanding the basic fields, you must understand that when you are holding a static field detector in your hand, you are connecting the field detector to ground potential.... so the part of the detector you are touching is grounded. If you are smart, then you will make the handle and the enclosure from conductive metal so the entire box will be grounded. You then have a good ground for the antenna to reference against the charges it will collect. The idea is to compare the charge in the air to the charge found at the ground. You should find an average of near 100-200 volts at the elevation where you are holding a charge detector. But the antenna will find only a fraction of this voltage, because the grounded box in proximity acts to hold down the voltage when the 200v air charge tries to raise the voltage of the antenna. When you are searching for anomalies of the air charge, you then probe around the air to see if you can find unusual variations. In this case "unusual variations" means a variation in the charge that you find in a place where there is no tree or bushes, or other thing in the landscape that would be expected to cause a change in the air charge that you are detecting.
That is the basic idea of a charge detector. But there are refinements which few hobbyists ever take notice of. For example, the Zahori charge detector has a special digital filter which unloads the antenna at a preset frequency which is set to be the same as the AC power frequency -- 50 or 60 Hz. The idea is to remove any interference from electrical power lines. This filter also will unload the antenna when there is no power line present, to keep the antenna circuit from becoming saturated with a strong charge that you might find from a large charged object. But the Zahori is a simple digital filter with limited capabilities.
There are other charge detectors which are much more sophisticated. Some designs have high quality notch filters to remove the AC power interference, and additional filters to remove other higher frequency electric fields. Some of the best charge detectors use a high impedance front end which is filtered to detect only extremely low frequency that might be found from slowly moving charged objects, or possibly some slowly changing geoelectric anomalies under the ground as you might find when telluric currents are in the process of transition as the sun moves and distant thunderstorms are causing fluctuations in the currents under the ground. These geoelectric anomalies do not indicate the presence of treasure, but if you are walking with a charge detector at a speed which corresponds to the filter you have installed, your relative motion could easily detect an anomaly that could be caused by buried metal under the ground. However, I would not expect any success unless you first did a good job to filter out all the much stronger interference that is found at the higher frequencies than 2-3 Hz.
A final thought about conductive boxes...
The metal box that is considered good design for static charge detectors is also considered good design for RF receivers which use dipole antennas, especially the 1/4 wave whip antennas and similar designs. In these cases, the ground plane is part of the antenna system. However, at lower RF frequencies like VLF and ELF, dipole electric field antennas are very poor for receiving a signal compared to a coil antenna wound as an air loop, or around a ferrite. When using a coil antenna, it is important to be very careful where you are placing metal parts near the antenna. Since they are receiving a magnetic wave, induced currents become important, and you can receive secondary magnetic waves from nearby parts of the enclosure. These secondary fields from the box will interfere with secondary fields that you may want to receive from metal under the ground. The effect is your receiver coil will become less sensitive to the metals located at a distance from the coil. It could have the same effect as taping a metal piece to your metal detector search coil, then adjust the ground balance to begin metal detecting. You will see your ability to detect deep metals is not working as well as when you remove the metal from the search coil.
In the case of a coil receiver for RF, if the coil is completely enclosed by a metal box, you could prevent the magnetic signal from entering the inside of the box to reach the receiver coil if the metal is a magnetic flux conductor. And if it is not a magnetic flux conductor, then it could generate secondary magnetic fields which cause interference to the reception of the receiver coils.
When I look at the Mineoro circuits, I see a an electrostatic detector combined with a VLF regenerative receiver. I see they have two loops on printed on their circuit board, with the electrostatic part having a passive loop behind it. This loop has no direct connection to the ground by any conductive path through the person who holds the box. So what we have in the Mineoro FG locator is a wooden box which is insulated from the grounded hands of the treasure hunter. This condition allows the box to take on the voltage of the air around it. Since the treasure hunter's hand is located a few inches away, the circuit board will attain only a small static voltage, as if it was held only a few inches above the ground. So we expect the negative ground on the circuit board holds a static air charge of maybe 10 volts due to its proximity to the treasure hunter. This becomes similar to being grounded, but with the added disadvantage of fluctuating as the treasure hunter moves his hands and walks in ways that can cause static voltage fluctuations of the proximity field around the electronics of the circuit.
Best wishes,
J_P