BFO is the simplest form of metal detection technology, often used in entry-level or DIY kits. Uses two separate oscillators to create an audible beat. Frequencies shift when the search coil passes over metal.
The table below summarizes the key differences between the editions:
V. Practical fieldwork and methodology
A key detail for anyone referencing the PDF file is the book’s publication history. The "Inside the Metal Detector" PDF you may have encountered is likely the , published by Geotech Press in 2015 . This edition was a revised and updated version of the original, which debuted in September 2012 .
The idea for the book came about almost by accident, born from a recognized gap in available literature. George Overton explains: "Although there are many books available on 'how to use your metal detector', and numerous others dedicated to particular types of finds, there was a complete lack of any detailed information on the innards of the metal detector itself" . Carl Moreland added that both he and George had independently searched for such a resource and, finding none, began writing their own books. When they discovered each other's projects, they decided to merge their efforts. With Moreland's focus on technology and Overton's expertise in Beat Frequency Oscillator (BFO) , Transmit-Receive (TR) , and Very Low Frequency (VLF) designs, the collaboration resulted in a very comprehensive final product. Inside The Metal Detector George Overton Carl Moreland.pdf
Before this PDF existed, information about how metal detectors actually worked was fragmented. Manufacturers kept their schematics proprietary, and hobbyist literature was either too simplistic (user manuals) or impossibly academic (physics journals).
The PDF explains mathematically why a concentric coil creates a cone-shaped detection field and why a DD coil creates a blade-shaped field. More importantly, it explains the "null" point—the exact voltage balance required to make a detector quiet over ground but loud over a coin. BFO is the simplest form of metal detection
For the hobbyist, "Inside the Metal Detector" is a true project book. It offers several hands-on experiments and complete, buildable detector projects, providing a tangible way to learn the theory. These projects are designed to be both educational and functional, allowing users to understand each stage of detector operation. Some of the projects mentioned include:
Individuals who want to graduate from building basic radios to constructing complex geophysical instruments. The table below summarizes the key differences between
The text delves deeply into the geometry of VLF search loops (such as Double-D and Concentric coils).