Geotech – technology for treasure hunting

Molecular Frequency Discriminator (MFD) has become a popular term to describe electronically-enhanced dowsing rods. Low high pass filter There are two components to the typical MFD: a signal transmitter, and “receiver” L-rods. High pass filter output voltage Construction of the L-rods is covered in the Building LRLs report and will not be repeated here. Butterworth high pass filter design pdf We will focus on the signal generator.


The prevailing theory behind MFDs is that the signal generator transmits at a frequency that matches the “molecular resonant frequency” of a desired target. Passive high pass filter calculator The most common frequencies used are 5KHz for gold and 8.7KHz for silver; other elements have different frequencies but we will focus only on gold and silver. Filter high pass Therefore we need a signal generator that can switch between two different frequencies.

There are many ways of generating signals, with tradeoffs in circuit complexity, accuracy, stability, and flexibility. How to set high pass filter Accuracy refers to the ability to tune to an exact frequency; stability describes how well the generator can maintain a certain frequency over time and with temperature variations; and flexibity means how easy it is to change the frequency or amplitude.

The simplest is probably a ring oscillator, the most complicated might be a crystal-controlled Direct Digital Synthesis (DDS) chip. High pass filter response The ring oscillator, while incredibly simple, has poor accuracy, poor stability, and moderate flexibility. High pass filter bandwidth DDS offers the precision and stability of a crystal oscillator while adding the flexibility of millihertz tuning. High pass filter inductor In between are a wide variety of methods, including a couple of fairly simple yet flexible function generator chips.

One such chip is known as the “8038” (originally made by Intersil, and now produced by several companies) and provides a reasonably clean sinusoidal output as well as triangle and square waves. 1st order high pass filter The output frequency is set by a few external components so it is easy to use, and it is inexpensive. When to use high pass filter Another similar chip is the Exar XR2206, which has a little better stability and cleaner waveform than the 8038, but is harder to find. Waves high pass filter We will use the 8038.

Figure 1 shows the 8038 signal generator circuit. Circuit diagram of high pass filter This is a very standard configuration given in the Intersil data sheet. Second order high pass filter circuit The output frequency is set by R1 and C1 (plus C2) to be approximately f=0.15/(R1*C1). Rl high pass filter transfer function The sine wave output at pin 2 is then fed through an R-C low-pass filter (R4-C3) to the LM386 audio amplifier. Iir high pass filter design theory Figure 2 shows the PC board for this circuit. First order high pass filter Note that the PC board includes some extra pads for optional circuitry that is not used in this project.

Since this MFD is only designed for gold and silver there are only two frequency selections and therefore the 8038 only needs two capacitors. High order low pass filter One capacitor (C1) is always connected to the 8038 and results in a frequency of 8.7KHz. What is a high pass filter audio S2 switches in a second parallel capacitor (C2) that decreases the frequency to 5KHz. First order high pass filter transfer function The low-pass filter (R4-C3) has a cut-off frequency of around 10KHz and helps suppress the output harmonics of the 8038 for better spectral purity. Diy high pass filter Finally, the LM386 provides gain and drive capability for the ground probes.

The only drawback to using an 8038 is that it requires more than 9v to operate, therefore it cannot be run from a single 9v battery. High pass lc filter An 8-pack of AA’s will produce 12v which is barely sufficient; 2 series 9v batteries is the best solution. High pass filter transfer function You should put the circuit board in an appropriate enclosure: my solution is shown in Figure 3, with the batteries inside the case. Transfer function high pass filter The enclosure has a power switch, a frequency select switch, a battery test switch and LED, amplitude knob, and two banana jacks for signal outputs.

The amplitude adjust potentiometer R5 allows the user to vary the output signal level which determines the maximum distance the MFD will detect a target. Sallen key high pass filter transfer function You can eliminate the pot and make R5 a fixed 50K resistor for a fixed full-power output. High pass filter matlab code download As shown, the battery check circuit is designed for 18v operation and will cease working when the battery voltage drops to about 13v. Variable high pass filter circuit You can eliminate the battery check portion of the MFD if desired.

Once we have the circuitry working what do we do with it? We will do what every other MFD manufacturer does: connect the output leads to probes that are stuck in the ground. Rc high pass filter cutoff frequency Each probe consists of: a short (6″) piece of 2″ PVC pipe, two 2″ end caps, a 12″ length of 3/16″ brass rod, a banana jack, a wire clamp, and some wire. High pass filter photography Figure 4 shows the material needed to make two probes.

First, use a high-quality drill bit and drill a 3/16″ hole through the center of one of the end caps and just slightly into (but not through) the inside roof of the other end cap (see Figure 5). High pass filter adalah The brass rod should slide through the hole with a considerably tight fit which is why you want to use a high-quality drill bit. High pass filter audio Cheap bits tend to have inaccurate sizes. High pass filter circuit using op amp Drill a hole in the side of the 6″ long pipe to accept the banana jack and solder the wire to the jack. High pass filter pdf Assemble everything but the top end cap. High pass filter ecg You may want to clean and paint the short pipe section for a sharp appearance.

With the rod pushed through the assembly by a couple of inches use the clamp to attach the wire to the rod (Figure 6). High pass filter explained Finally, add the top end cap making sure the rod goes into the half-hole in the inside roof, then push everything together. High pass filter symbol You may want to add PVC cement to the end caps and some epoxy where the brass rod goes into or through the end caps to hold everthing together securely. High pass filter derivation Sharpen the tips of the probe rods (to about 45-60 degrees) to make it easier to push them into the ground.

In Figure 6 you may have noticed that the connecting wire from the banana jack to the rod is spiraled around the rod. Capacitor high pass filter This technique generates a molecular polarization field that is directly induced into the probe rod and eliminates all false (ghost) signals. High band pass filter The spirals should be wound in opposite directions for each probe. A high pass filter Once the probes are finished you will need to make a pair of banana wires to connect the MFD transmitter to the probes. High pass filter bode plot The finished probes are shown in Figure 7.

This concludes the instructions for the MFD transmitter. Uses of high pass filter Together with the L-rods described in Building LRLs the total package is shown in Figure 9. High pass filter theory The materials cost of this package should be around $50: $15 for the L-rods and $35 for the transmitter. Rc high pass filter calculator It is exactly equivalent to MFDs being sold for up to $2000.

At this point you should be ready to try out the MFD. High pass passive filter Insert the two probes into the ground about 2-3 feet apart. Frequency response high pass filter Using banana wires connect the probes to the MFD transmitter. High pass filter code Turn on the transmitter and grab the L-rods. What is low pass filter and high pass filter Walk a circle (about 10-12 feet out) around the probes until the L-rods cross – you have located a potential signal line. High pass filter noise Mark this point. What does high pass filter mean Imagine a line connecting the marked spot and the middle of the probe area. High pass filter on vocals Move farther away (say, 30 feet) along this line and, using the L-rods, try to locate the signal line. High pass filter c Continue moving away from the probes as long as you are able to detect the signal line. High pass filter online Make sure you mark all of your signal hits.

At some point as you move farther away from the probes you will cease detecting the signal line. Rc circuit high pass filter If you detect a signal line out to a certain distance from the probes but the signal seems to stop, then where it stops should be the location of the target. Difference between high pass and low pass filter Before you dig, you can verify this by moving the probes 90 degrees around the target point and triangulating. High pass filter laplace The target will be at the location where the signal lines cross.

There are two potential pitfalls with MFDs and both are due to the incredible sensitivity. Butterworth high pass filter theory An MFD has the ability to pick up target signals from as much as 10 miles away, though 1-3 miles is more typical. High pass filter working This means that it can take quite some time and effort to trace out the signal line. High pass filter noise reduction Once you have the target pinpointed you may have to face another problem: depth. Active high pass filter transfer function The MFD can detect targets as deep as 100-200 feet, so locating the target is only half the battle. High pass low pass filter If a metal detector does not verify the existance of a metal target at the identified location then you should bring in excavation equipment. High power low pass filter If no obvious target is found when you reach 200 feet, then the target was most likely subatomic gold particles – you cannot see it and most chemical analyses will not detect it either, but the MFD will.