Antenna, RF, Ground Scanning


    This page covers the Principles of Radio Waves and Antennas.

Below find an idea to build a GPR.


The Project:

    Looking for Gold?


Understanding the Wave, Cycle, and Beam pattern:

Beam Pattern, directing the Modulated Signal.

Build your own Antenna, a handy Calculator! (

    The Wave
Amplitude: (Voltage) is the height (size) of the wave.
Gain: How effective the Antenna sends and receives the wave.

    The higher the decibel, the more powerful the wave. High DB = High power.

    Power supplied to the Transmitter equates to propagation, high Wattage is good for Ground Penetration under wet conditions, but is very bad in open air, a powerful wave may hurt people and living things, and the wave will overtake other signals on that "Band" (frequency), or alter signals and cause distortion, note too that Side Lobes and the back of the Yagi can also emit and cause disturbance at high power.

(Chopping: removing the top or bottom of the wave)

Chopping a Wave upon receiving it, is called Band-pass. Used to filter signals, for example the tweeter speaker in your car, sending Low amplitude signals to that speaker along with sending high frequency to the subwoofer would cause unwanted results.


    Frequency is how often the wave occurs within a time frame, a High Frequency wave will not travel very far if faced with obstruction. In sound High Frequency would be a high pitch noise, a high pitch noise doesn't travel well threw objects, a low base on the other hand will. Using that analogy we'll build a GPR that uses a relatively LOW frequency in the general scope of things.

Low Frequency will travel further, in the case of a speaker and Sound Waves, Low Frequency creates a thump that you feel and a long wavelength, these waves have High Bandwidths and the peeks/ valleys are far apart, ELF in Radio is an example of a Low Radio Wave frequency band.

The 433MHz Arduino Transmitter Receiver modules that are being used in this project have a Band Width of 0.69 Meters, for every 0.69-Meters one cycle would have occurred, this wave is defined as an Ultra High Frequency Wave.

Frequency and Bandwidth are not directly proportionate, we need to consider Amplitude to calculate the size of the Band. Power is determined by multiplying Amperage*Amplitude; or Joules/Amperage = Amplitude; or Joules/Amplitude = Amperage

DB/ BDi:

Decibel is a unit of power, it is how much of the sent power is returned and used, and the amount of energy that's transmitted after generating the signal using a "Tank" Circuit.
The DB "Decibel"is a Logarithmic Equation like that of "Index Notation" (Powers of 103/ 102) or for example the Earth Quake "Richter Scale", all three are Logarithmic equations.

A High Gain antenna must be large, the size is measured in "Wavelengths", for an example a Full Wavelength Dipole Antenna used for this project will have to be 0.69-Meters long or 3.28084 Feet long. We make up for that by coiling wire, like in real-estate, we go up instead of out. We can use equations also to help us increase the Gain on receiving antenna like using Parabolic equations and deflectors.
High Gain/ Directional Antennas include the Parabolic Dish, the Yagi antenna, others are also in use.

DB gain for a receive antenna is the measure in Watts, for how well the antenna receives the radio wave energy.
Antenna Gain and Distance go hand and hand, Energy cannot be created or destroyed only transformed, the total amount of energy it would take to radiate in all directions while using a High Gain Antenna would be way too high, it would be greater than the sum of the transmitter power, making omnidirectional high gain transmitting impossible.


Impedance matching (resistance matching) is important when trying to detect or work with Radio waves, efficiency decreases as impedance miss match values increase, the Radio Signal will get lost in both cases of Transmission and Reception, at high levels of resistance (Impedance).


Propagation (sending) the radio wave, Frequency Propagation noted above is one part to Propagating a Radio wave, skipping, dead zones, polarisation (antenna positioning), time of day, time of year, solar radiation, all play a part in Propagating a Radio Wave.


A loss of wave power, attenuation occurs over distance naturally, as the wave moves away from the transmitting point it expands and moves away from itself, eventually becoming indistinguishable; or the wave hits objects and distorts/ absorbs into them.

Polarisation: If you have a Horizontally aligned antenna for sending, the Antenna for receiving needs to be in the same position, if the antenna is at a 90 or 45-degee angle from the Horizon, the receiving antenna should also be at the same 45-deg angle, if the antenna is positioned Vertically, the receiver Antenna should be the same.


If Amplitude equals the size of the wave, then how do we pinpoint small objects? How do we direct the wave to a point? We have one other issue, the Frequency being .69 meters long, combined this Band is quite large and will cover a large area. Solution: The Band-Pass Filter.

Yagi Beam Pattern:


GPR (Ground Penetrating Radio Project) Concept:

In theory a Transmitter and Antenna will emit a Directed Radio-Wave into the earth, the wave would continue on or dissipate from absorption of ground medians, such as Rock and water, however in some cases, the Radio wave will be received by an Omni directional Receiver Antenna from the Radio waves Reflection off minerals such as Pyrite, Tin, Gold, or Silver, the more conductive the more reflective, the collected data can later be plotted using software (see images below).

The Radio Receiver will be set to receive a Modulated Signal at a specific wavelength (frequency) of 433MHz, this signal will be logged in CSV format, this way it can be loaded/ imported, into a variety of different programs that generate charts or mathematical models, the signal is Modulated to carry a simple number or string for identification.

Experiment a little, try to detect some (1-Gram) of Gold and some Silver (an ounce or two) above ground, adjusting the angle of the Transmitter and Receiver until a signal is received by reflection, do this a few times and move over the Object to see if the signal is dropped or picked up when desired, from this move the Gold/ Silver strategically underground, dig a small hole in a Planter, mark the location and start testing by covering the Gold or Silver with different materials, pack down for different density, and add Water for moisture tests, ask questions and get answers to establish a Database.

After a Database has been established an equation from the found information can be used to adjust depth for different materials, a Sketch can also be written to monitor ground condition/ composition based on the Data store.

To make it work a Radio wave has to reflect off of an object like Gold, then skip up toward the Receiver Antenna, in all other cases the Radio wave should just keep going, and/ or dissipate into the earth, returning no reading, each reading will be recorded and exported to csv format for generating a plot/ graph later (see images below) showing exact location of each hit along a specific length plain.


The speed the sensor travels across ground will not matter much, only a specific depth can be plotted each pass, and the data is being plotting to a grid, by using a defined distance (the distance traveled over a Fifty-foot linear Plot measured using a 50' Tape), if too many returns are received within a period of time some of the returns can be ruled out automatically, the returns just wouldn't fit in the plotted (allocated) distance, time simply does not matter in this case, only distance traveled.

The Radio wave should be modulated, this way specific waves sent from a transmitter can be precisely plotted.

All that's required to make this idea work is a return over distance, it can be any value chosen, not just the number "1" one or "0", the goal is to receive the Data as CSV, then using a Personal Computer and a program like Excel plot in 3D, all the returned readings (if any) over distance, please see the images below from testing the Transmit Antenna using the Receiver.
Do we fly, or do we drive over the ground?

The angle of the Wave being sent from the receiver antenna will change position on the plotted path if Driving Over a large object, if other sensors and Mechanics are not used to reposition the antennas, data acquisition loss will take place while driving over objects.

Flying maybe the best idea, but what if a flying machine isn't available?

A Zip-Line and tether can always be used, it can be designed to give a maximum travel distance of fifty feet and keep the sensors (Transmitter Receiver) level; microcontrollers, motors, and a sensor module can be used to adjust for any wind problems on the fly, same as the case with the Truck above if it's moving over objects and changing the Propagation (sent) angle.

Passing over the same line and adjusting the sensor angle along with transmitter power will make plotting a 3D view of what's underground possible, section by section the earth below can be sliced into images from plotted lines. Trees are no problem if the Antennas can pass over them, wood and cardboard do not attenuate (resist) the signal very much.

To make this work the sensors (Antennas) need to be adjustable, attenuation (resistance) also needs to be considered, wet soil will prevent the Radio Waves from penetrating the Earth any real distance, for example if the Angle of the Transmitter and Receiver is set for a deeper scan wet ground may prevent any returns at all.

That's all for theory, time to start building and testing.
Below are some results from a test of the above Yagi antenna, a link to an online Calculator can be found above if you want to make your own Yagi, as seen in the above image the Yagi used in this example has a Wood Dowel boom, the Director, Reflector, and Driving Elements are Coper Tube.

Using the values provided from the Online Calculator four pieces of Coper where cut and fastened to the Boom, one Driving Element is connected to Ground via Coax (Impedance Matching, 50-Ohm for the receiver) and the other to the Antenna I/O via Coax on the Module.

The Transmitter Antenna needs to be Directional, the Receiver Antenna may work as an Omnidirectional (All direction) Antenna.

The Transmit Antenna needs to be tested safely and legally, so let's test using the receiver module and Arduino by uploading some code below to the Arduino Microcontroller.
Origin Website url ,

This code:

Without using a transmitter the above code gave the below results using Excel:


How to make a graph:
Add a Comma to The Spacers used in the Code Above, with the Arduino connected open the Serial Monitor, under Tools in the Arduino IDE GUI, let the list run for a while, unplugged the Arduino from the PC leaving the Serial-Monitor open when enough data's collected, copy the code using the H-Key command "ctrl and C" at the same time (Windows Operating System), pasted it to a Text File and save as a CSV File.
A CSV (Comma Separated Value) file can be loaded into Excel or OpenOffice, actually any Database you like, for example a MySql Database in Web Design, a UI (User Interface) called "PHPMyAdmin" can be used to load any CSV for future analysis into a Mysql table. Any "Structured Query Language" Database works with CSV files.
With the code loaded in Excel select all the Columns and "Insert" a Graph from the Insert/ Graph in the menus bar above.
More results:

Soil Penetration Tests:
More on this topic to follow:
Modulation Sketch for Transmitter and Receiver.
Receive RF:

#define rfReceivePin A0  //RF Receiver pin = Analog pin 0

 #define ledPin 13        //Onboard LED = digital pin 13


 unsigned int data = 0;   // variable used to store received data

 const unsigned int upperThreshold = 70;  //upper threshold value

 const unsigned int lowerThreshold = 50;  //lower threshold value


 void setup(){

   pinMode(ledPin, OUTPUT);




 void loop(){

   data=analogRead(rfReceivePin);    //listen for data on Analog pin 0



     digitalWrite(ledPin, LOW);   //If a LOW signal is received, turn LED OFF





     digitalWrite(ledPin, HIGH);   //If a HIGH signal is received, turn LED ON






  RF Blink - Transmit sketch 
     Written by ScottC 17 Jun 2014
     Arduino IDE version 1.0.5
     Transmitter: FS1000A/XY-FST
     Description: A simple sketch used to test RF transmission.          
 ------------------------------------------------------------- */
 #define rfTransmitPin 4  //RF Transmitter pin = digital pin 4
 #define ledPin 13        //Onboard LED = digital pin 13
 void setup(){
   pinMode(rfTransmitPin, OUTPUT);     
   pinMode(ledPin, OUTPUT);    
 void loop(){
   for(int i=4000; i>5; i=i-(i/3)){
     digitalWrite(rfTransmitPin, HIGH);     //Transmit a HIGH signal
     digitalWrite(ledPin, HIGH);            //Turn the LED on
     serial.print(1 Pin High);   //Print “1 Pin high” to the Serial Monitor
     delay(1000);                           //Wait for 1 second (resolution)
     digitalWrite(rfTransmitPin,LOW);      //Transmit a LOW signal
     digitalWrite(ledPin, LOW);            //Turn the LED off
         delay(i);                            //Variable delay
So after all that.... What does CNC have to do with Antennas and RF? 
RF is used in Remote Control of CNC'd things.

Other Project Examples that use Arduino and the RF Radio Transmitter Receiver Module:

Assemble, experiment, enjoy! But please follow the rules, some frequencies and transmit frequencies are prohibited and some can cause personal harm, interfering with any Emergency Service is Prohibited by Law.

For as far back as we know Gold has been the most valuable commodity for art and trade, Gold not only is rare, but it's not like other metals, it's conductive but it's not ferrous, or magnetic, making Gold hard to trace.

Gold today is still hard to find, some tools can be used for extraction of the rare metal, even some other metals can be used to help, for example Mercury, but there isn't much for new technology.

Sure today there are Metal Detectors, VLF detectors can locate Gold, but they aren't the best at it. Modern GPR can't be used for detecting gold, however that maybe because of the way the Modern GPR is configured and/ or programmed, it could be the way the modern GPR is designed.  

GPR (Ground Penetrating Radar) is a method used to survey objects located underground by use of Radar.

For this Project, instead of Radar the chosen Bandwidth will be in the UHF Radio Band opposed to the Radar Band. The idea is to direct Radio Waves into the Earth that get absorbed by non conductive materials, and reflecting conductive materials, reflected, received waves are then logged and mapped out, in this case Gold and Silver are the target testing elements.

This project will in this case work on the UHF (Ultra High Frequency) 433MHz Frequency, or a 0.69 Meter-Band, so instead of a GPR "Ground Penetrating Radar", we'll have a “Ground Penetrating Radio”.

Radio is not limited to the 433MHz UHF Receiver/ Transmitter modules used in this project, or the Radio used in a Car, Radio extends to Radar, WiFi, even Bluetooth.


0Tue, 23 Jan 2018 09:54:52 -0600 0