In 1962, I built a BFO metal detector of my own design in high school electronics. My instructor entered it in the California State Fair and it won the blue ribbon that year. It just pitted two oscillators against each other, with one being controlled by the operator and the coil of the other being at the end of a broomstick. The judges said "it looks crappy but it works good." It would detect a quarter at about 4".
I found a silver nugget with it, near an old smelter in the gold country of the Sierra Nevada Mountains, near Mokelumne Hill. After that, I built another, much simpler one, which pitted the single coil's oscillator aganst a six transistor radio station, for the bfo works. You listened to that squeal on the radio as you searched. It also worked very well, and I found many coins with it in my mom's front yard. That yard eventually yielded up over 100 coins, to my various detectors.
I could not keep up with the newer models coming out, so I finally had to start buying top-of-the-line models as they came out. I had Whites, Big Bud Pro, Technetics, Gold Mountain, Compass X-100, Garrett's, and Garrett's GTI 2500, a fantastic machine that all but eliminates digging up any trash at all!
The Gold Mountain machine was a big step down from my Technetics with no ID-ing capability at all. But after work and evenings and weekends, I found 750 coins within my first 30 days with it.
No one had ever searched the grassy parking strips (only about 1 1/2 feet wide) along our sidewalks before. They were full of coins, from a 1900 Indian Head at a half inch on up to mercury dimes and war nickles, silver quarters, and rings too. The neighborhood only started being built up in the late 1930's. All of those 750 coins were within only two blocks of my home, in one month, with a non-ID detector.
