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Offline GarrettManRPTopic starter
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« on: June 06, 2020, 11:52:07 pm »
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Hi folks! I'm new here and looking forward to discussing some things. For example, What determines the sensitivity of the search oscillator? Does running the oscillator at the absolute minimum gain make the circuit more sensitive? My understanding was that you wanted the maximum voltage possible on the coil so the magnetic field would be the strongest but my tests have shown that larger peak to peak voltage on the coil does not improve detection range for the same size target. My old homemade beachcomber BFO originally ran on 6 or 9 volts. I have tested up to 30 volts and detection range was not noticeably different. I have noticed for years that most detectors run on pretty low voltage so that must not make any difference as strange as that sounds. I am going to breadboard the colpitts again and test with minimum gain to see if it matters but I wanted to ask here to see what others think or better yet have someone who knows to explain it.

Thanks.

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Offline nickel_n
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« Reply #1 on: June 08, 2020, 07:12:28 pm »
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if you haven't look at this book all ready

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https://www.amazon.com/Inside-Metal-Detector-George-Overton/dp/0985834218

its a good way to get started

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« Reply #2 on: June 08, 2020, 08:12:34 pm »
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Hello again GarrettManRP  . Besides the book that Nickel-N was talking about,
I'm looking now for BFO and VLF reference folders or schematics for you to read that I will try to post here.

But in the meantime since we are talking about BFO Machines, the Very First Metal Detector I bought was from Lafayette Electronics back in 1971 in Tacoma, Washington. Store was located off of Steilacoom Blvd/South Tacoma . I bought it for $49.95 !!!

It was the Bounty Hunter 1 , the cheapest one. It worked great !!!  Found several Buffalo Nickels and some Big Military Bullets dated 1917 over by Browns Point Beach in 1971 !!!

Great Memories

Stay Safe................Eugene

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Offline GarrettManRPTopic starter
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« Reply #3 on: June 08, 2020, 08:37:03 pm »
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Very cool!
A funny coincidence, I live in ďLafayetteĒ Va.

My Dad built the beachcomber from popular electronics July 1967 back in the late 60ís. That was the first detector I ever new. I built one using the same circuit in college. I have always had ideas for improving the depth but never had the time until recently. Now Iím tinkering again. My Brother and I metal detect around some old homesteads once in a while and we like to dig everything anyway so the BFO is ok for that. Using a homade detector from the 60ís makes it more fun somehow.

That old beachcomber operated at higher frequency though, around 500kHz I think. Thatís higher than most BFOís that came later. About the best we ever did on coins was 6 inches from a 6Ē coil. And of course you only have ferrous vs non-ferrous discrimination.

Looking forward to seeing the material you are looking for.

Thanks.

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« Reply #4 on: June 09, 2020, 08:07:48 am »
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Welcome!

The coil itself has more impact on depth but only to a degree. At some point your electroinics can't drive the coil so it's a balance you need to determine.

Let me know your level of expertise and we can discuss this further. I am a semi-retired engineer and don't want to pile snow on your enthusiasm. We had a member here that I tutored in the past but he passed away way too soon. I took him from a multimeter level to programming microcomputers. Smart man. I miss him.

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It's all about that moment when metal that hasn't seen the light of day for generations frees itself from the soil and presents itself to me.
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Offline GarrettManRPTopic starter
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« Reply #5 on: June 09, 2020, 11:58:15 am »
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Sorry for the loss.

I am not an engineer by schooling but I worked as a technician at a mobile robotics company for about 6 years and have been a tinkerer since childhood. Iím still learning though. Iím playing with oscillators and looking to improve on the old BFO design as a learning experience. Iím interested in determining what makes the colpitts oscillator the most susceptible to inductance change. From circuit design to types of capacitors (low resistance and temp stability) to the type and size of coil wire (Litz?). The old BFO from the 60ís used 50+ year old technology. Iím thinking that using modern tech it can be made better. Granted it will still be a BFO but Iíd like to think it can be made to detect deeper be more stable and I plan to add a meter.
I am interested in learning more about EM fields with focus on detectors. I recently researched field shaping and found some interesting articles but nothing that I can apply to detectors as of yet. Anything that can increase the effectiveness of the EM field is interesting to say the least. For 50 some odd years we have been working under all the known limitations. Iím trying to think outside the box.
Iíd even like at some point to add an onboard micro controller and get into some signal processing.
So that maybe shows you where Iím going. I have also done some pic32 project work communicating with I2c sensors, rs232, designed and built motor controllers, amplifiers, pic32 motherboards, used xbee radios, circuit board layout, use meters, scopes etc. I am also a software developer.
Having said all that I think I have more desire and interest in things than I have skills to back up but thatís the curse of being a jack of all trades.

Any help and discussion is welcome and appreciated.


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