Build one of the simplest Cave Radios possible, DIY or from a kit
Radiolocator Kits Available!
Finally a cave radiolocation and thru-the-Earth magnetic communication device that can be assembled by anyone with basic shop and soldering skills, with no test equipment required.
Because of their limited vertical and horizontal range, these radios are intended mainly for use in smaller/shallower caves, locating new entrances, and for demonstrations, practice, etc.
The performance is modest, but a pair can be constructed in a weekend, and with the two-way capability they are great fun.
This radio, named the Basic-1, uses a single dual op-amp IC to perform both receive and transmit (beacon) functions in one unit. The operating frequency is 1750 Hz. Transmit can be either CW (Morse Code) or a beacon pulsing 5 times/second. The loop antennas are 19 inches (48cm) diameter. A single 9V radio battery will power a radio for days, even in transmit mode. A pair of Basic-1 radios can communicate straight down through 200 feet (60 meters) of rock in ideal conditions. Accurate Radiolocation (which requires a strong signal for sharp signal nulls) is limited to about 67 feet (20 meters) depth.
Another version of this radio, the Basic-2, uses a second dual op-amp and a heavier loop to improve receiver performance and greatly increase the transmitted signal. The Basic-2 costs significantly more to build because of the high cost of copper wire, and has half the battery life, but increases range to 300 feet (90 meters) for communicating and 100 feet (30 meters) depth for Radiolocating. The signal drops off as the cube of range (doubling distance drops the signal to 1/8), which makes long ranges difficult with simple equipment.
Finally a cave radiolocation and thru-the-Earth magnetic communication device that can be assembled by anyone with basic shop and soldering skills, with no test equipment required.
Because of their limited vertical and horizontal range, these radios are intended mainly for use in smaller/shallower caves, locating new entrances, and for demonstrations, practice, etc.
The performance is modest, but a pair can be constructed in a weekend, and with the two-way capability they are great fun.
This radio, named the Basic-1, uses a single dual op-amp IC to perform both receive and transmit (beacon) functions in one unit. The operating frequency is 1750 Hz. Transmit can be either CW (Morse Code) or a beacon pulsing 5 times/second. The loop antennas are 19 inches (48cm) diameter. A single 9V radio battery will power a radio for days, even in transmit mode. A pair of Basic-1 radios can communicate straight down through 200 feet (60 meters) of rock in ideal conditions. Accurate Radiolocation (which requires a strong signal for sharp signal nulls) is limited to about 67 feet (20 meters) depth.
Another version of this radio, the Basic-2, uses a second dual op-amp and a heavier loop to improve receiver performance and greatly increase the transmitted signal. The Basic-2 costs significantly more to build because of the high cost of copper wire, and has half the battery life, but increases range to 300 feet (90 meters) for communicating and 100 feet (30 meters) depth for Radiolocating. The signal drops off as the cube of range (doubling distance drops the signal to 1/8), which makes long ranges difficult with simple equipment.
Basic-2 Radiolocator with loop formed from PVC electrical conduit
I have assembled several radios and loop antennas that have been range-tested on the surface. During testing in an open field I detected noise from power line harmonics that I eventually traced to a buried wire that I was able to Radiolocate and follow for hundreds of feet. The abandoned wire was not connected to AC power at either end. Apparently, magnetic fields and/or earth currents from distant power lines induced current in the wire. Later, I found a second abandoned wire in an adjacent field! This is another good use for a sensitive broadband audio frequency receiver. One successful cave Radiolocation test was done with a Basic-1 in less than ideal conditions.
I have put together a few kits with most of the required parts including PC board, case, Telex 610 mono 600 Ohm headphones, wire, controls, connectors, knob, and electronic parts, which are 100% thru-hole. Not included is the battery, the bubble levels needed for accurate locating, the loop form, the loop wire, and the optional piezo sounder (a Radio Shack item). Links to documentation for assembly and use are found below. t would not be difficult for an experienced person to assemble a radio from junk box parts even without the PC board, but some test equipment might be necessary for frequency alignment. I am selling at my cost as a service to the small Cave Radio Community. If there is enough interest, quantity purchases should bring the prices down.
The following costs exclude postage. Contact me for a quote at the email address on the bottom of this page. I will take a personal or bank check, or PayPal. PayPal will be 5% extra if you are paying by credit card rather than withdrawing from a PayPal account. Note that you do not need to have a PayPal account to send money. I will send you the name of my PayPal account.
A single Basic-1 radio kit is $34.00. You must purchase your own loop wire (~$17.00) plus 2 bubble levels (~$4.00) bringing the total cost to ~$55.00 not counting the loop frame, optional piezo sounder, or battery.
Note that you you need two Basic-1 radios and loops to do radiolocating, bringing the total to ~$110.00.
A single Basic-2 radio kit is $35.00. You must purchase your own loop wire(~$30.00) plus 2 bubble levels (~$4.00) bringing the total cost to ~$69.00 not counting the loop frame, optional piezo sounder, or battery.
Two Basic-2 outfits will cost ~$138.00. I recommend the Basic-2 for it's better performance.
For those with a well stocked junk box, I will sell the PC boards at my cost of $4.25 plus postage. These are professional epoxy double-sided boards with plated-thru holes.
Note that the two parts kits are not interchangeable because the values of the loop tuning capacitors are different. The loop wire gauges are also different. However, the same PC board is used in both kits.
A complete history and technical description of the Basic-1 and Basic-2 radios, including specs, schematics, and parts lists are found in the PDF article The Simplest Radiolocator .
Complete assembly instructions for the kits are found in the PDF article Constructing the Basic-1 and Basic-2 Radiolocator/Communicators from kits. If constructing from my kits, I highly recommend printing out the following 3 PDF sheets and laying out each of the small parts on them before starting construction. This should avoid installing resistors or capacitors in the wrong place, and ensures that you have all of the correct parts.
Parts for the PC board
Front Panel parts
Additional parts to make the radio a Basic-1 or Basic-2
The Basic-2 radios can be constructed with different diameter loop antennas. See the PDF loop antenna table.
A French translation including schematics and parts lists is found in the PDF document MONTAGE ET UTILISATION DES BPS BASIC-1 /2 Traduction Dominique ROS. Note that this has not been updated recently!
See Locating Ground Zero to understand the shape of the magnetic fields and how to use them to easily locate the point directly over a beacon placed in a cave.
Print out the Depth Table to estimate the depth of the cave after locating ground zero. To estimate depth, move horizontally a known distance from ground zero (a distance similar to your guess of the depth is good), then tilt the loop away from ground zero (with loop axis aimed at ground zero) to find the signal null. Measure the tilt angle from vertical; find the d/l value for this angle; then multiply by the distance to ground zero to find the depth. For example if the angle is 20 degrees and ground zero is 10 meters away, the depth would be ~42.4 meters.
Practice, practice, practice, before attempting a cave, even inside a 2-story house or barn! I am always available to answer any questions.
NOTE! Stan Sides built a pair of Basic-2 radios and in Dec 2013 used them to do a radiolocation in Mammoth Cave at the end of Little Bat Avenue at a depth of about 120 feet. This is the radiolocation depth record for these radios as far as I know.
I have assembled several radios and loop antennas that have been range-tested on the surface. During testing in an open field I detected noise from power line harmonics that I eventually traced to a buried wire that I was able to Radiolocate and follow for hundreds of feet. The abandoned wire was not connected to AC power at either end. Apparently, magnetic fields and/or earth currents from distant power lines induced current in the wire. Later, I found a second abandoned wire in an adjacent field! This is another good use for a sensitive broadband audio frequency receiver. One successful cave Radiolocation test was done with a Basic-1 in less than ideal conditions.
I have put together a few kits with most of the required parts including PC board, case, Telex 610 mono 600 Ohm headphones, wire, controls, connectors, knob, and electronic parts, which are 100% thru-hole. Not included is the battery, the bubble levels needed for accurate locating, the loop form, the loop wire, and the optional piezo sounder (a Radio Shack item). Links to documentation for assembly and use are found below. t would not be difficult for an experienced person to assemble a radio from junk box parts even without the PC board, but some test equipment might be necessary for frequency alignment. I am selling at my cost as a service to the small Cave Radio Community. If there is enough interest, quantity purchases should bring the prices down.
The following costs exclude postage. Contact me for a quote at the email address on the bottom of this page. I will take a personal or bank check, or PayPal. PayPal will be 5% extra if you are paying by credit card rather than withdrawing from a PayPal account. Note that you do not need to have a PayPal account to send money. I will send you the name of my PayPal account.
A single Basic-1 radio kit is $34.00. You must purchase your own loop wire (~$17.00) plus 2 bubble levels (~$4.00) bringing the total cost to ~$55.00 not counting the loop frame, optional piezo sounder, or battery.
Note that you you need two Basic-1 radios and loops to do radiolocating, bringing the total to ~$110.00.
A single Basic-2 radio kit is $35.00. You must purchase your own loop wire(~$30.00) plus 2 bubble levels (~$4.00) bringing the total cost to ~$69.00 not counting the loop frame, optional piezo sounder, or battery.
Two Basic-2 outfits will cost ~$138.00. I recommend the Basic-2 for it's better performance.
For those with a well stocked junk box, I will sell the PC boards at my cost of $4.25 plus postage. These are professional epoxy double-sided boards with plated-thru holes.
Note that the two parts kits are not interchangeable because the values of the loop tuning capacitors are different. The loop wire gauges are also different. However, the same PC board is used in both kits.
A complete history and technical description of the Basic-1 and Basic-2 radios, including specs, schematics, and parts lists are found in the PDF article The Simplest Radiolocator .
Complete assembly instructions for the kits are found in the PDF article Constructing the Basic-1 and Basic-2 Radiolocator/Communicators from kits. If constructing from my kits, I highly recommend printing out the following 3 PDF sheets and laying out each of the small parts on them before starting construction. This should avoid installing resistors or capacitors in the wrong place, and ensures that you have all of the correct parts.
Parts for the PC board
Front Panel parts
Additional parts to make the radio a Basic-1 or Basic-2
The Basic-2 radios can be constructed with different diameter loop antennas. See the PDF loop antenna table.
A French translation including schematics and parts lists is found in the PDF document MONTAGE ET UTILISATION DES BPS BASIC-1 /2 Traduction Dominique ROS. Note that this has not been updated recently!
See Locating Ground Zero to understand the shape of the magnetic fields and how to use them to easily locate the point directly over a beacon placed in a cave.
Print out the Depth Table to estimate the depth of the cave after locating ground zero. To estimate depth, move horizontally a known distance from ground zero (a distance similar to your guess of the depth is good), then tilt the loop away from ground zero (with loop axis aimed at ground zero) to find the signal null. Measure the tilt angle from vertical; find the d/l value for this angle; then multiply by the distance to ground zero to find the depth. For example if the angle is 20 degrees and ground zero is 10 meters away, the depth would be ~42.4 meters.
Practice, practice, practice, before attempting a cave, even inside a 2-story house or barn! I am always available to answer any questions.
NOTE! Stan Sides built a pair of Basic-2 radios and in Dec 2013 used them to do a radiolocation in Mammoth Cave at the end of Little Bat Avenue at a depth of about 120 feet. This is the radiolocation depth record for these radios as far as I know.
Stan Sides at Radiolocating at Mammoth Cave