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Does Anyone Still Make BFO Detectors


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On subject of coils and systems... I was out working some areas for relics with a couple others and one guy was killing it with an very vintage 70s Garrett Master Hunter BFO unit with a large home made looking square coil of pvc looking material. After looking into I found that BFO is Beat Frequency Oscillator and was popular before T/R VLF format machines. BFO was not good for small coin shooting and nugget hunting and lacked ability for quality discrimination from what I read but excelled in depth ability, especially on large ferrous cache targets as well as finding mineral deposits like drifts of black sands or veins of ore.

So are there currently any units that still use a BFO mode or format? I can find vintage BFO type units available very reasonably priced, is there any information out there on how to bring them up to current on a battery system and build large coils suitable for this type of cache detecting?

 

 

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That is news to me - BFO was on the way out when I got my first detector in 1972 and I went with that new-fangled T/R tech instead. BFO units have no ground canceling capability and so depth is extremely limited by today's standards. I have not heard of any sold new in many years. Another article by Carl Moreland BFO Theory

Garret was a major manufacturer of BFO units and most used ones seen for sale were made by them. Here is their generic operating instruction manual.

2009 thread about looking for BFO detectors

1976-garrett-master-hunter-bfo-metal-detector.jpg

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I get that BFO tech is a dinosaur in most of today's THers eyes... but like a two box or double coil T/R system it seemed to be very useful in finding deeply buried caches of ferrous materials. Really not a system that would interest most searching for other targets. From what I witnessed a unit like shown below that he had modified some and using a large 2 foot search coil he was very productive in finding caches of cans and bottles in privies up to 4 foot or better (large concentrations of rusting metal) which he said was producing a huge halo effect around the target.

I was using a 2 box system and a new PI unit and doing ok, but what most struck me was the other user's ability to only get readings on the larger deep targets in areas heavily infested with smaller metal and lots of surface debris he was able to work through and just find the deep pits with his system. Though I am sure much of his ability was user based on experience and knowledge of his reading signals as much as the actual hardware.

 

Thanks for further info Steve. I think I will work on building a BFO platform off an vintage unit and homemade coil and see if I can get any results. found some info here too on such... http://www.hobby-hour.com/electronics/s/bfo-metal-detector.php

 

On another note, I did see several forums where guys were still using such BFO units to find deposits of black sands not detectable with other detection modes.

Garrett Master Hunter 1.jpg

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I've got one of the old Master Hunters. It was the first detector I ever owned. It came with two sets of dual coils. You can select which coil you use by flipping a switch. Mine still works, though i rarely use it. A few years ago, when it was the only MD I owned, I used to locate my property boundary stakes.

Jim

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BFO detectors were popular in the 60's & 70's as the detecting hobby emerged. They were super-easy & cheap to build, a simple design can be made with only 3 transistors. Anyone could become a detector manufacturer. Garrett probably had the best designs, and they were about the last to continue making them, up til the early 80's.

BFO is not good on depth, in any category. That's why no one makes them any more. The only thing BFO did that was semi-unique was respond well to mineralization, something you normally don't want, unless you are tracking black sand deposits. But you can actually do that with some VLF models, if you know how.

Besides having the best BFO, Garrett also made the best assortment of coils. Here's an old photo of my vintage collection, in the middle is a Garrett BFO with the 24x24" square coil. It's easy to build a custom coil, it's just a single coil of wire, I think the inductance is around 500uH. Shielding is important because it's very sensitive to ground capacitance.

collection2002.jpg

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Impressive collection Carl! being a collector at heart I have thought about collecting those vintage units myself, have even owned a few back in 70s shown there. Thinking about it my very first detector was a brown Bounty Hunter Pro model and had a mineral/ metal tuning knob on it, so it was likely a BFO unit and it really was challenged for depth with is smaller coil. Though being a novice Im sure user error played a big part in my lack of success too!

From reading Carl's Geotech site there are likely better projects for me to focus on than BFO for deep metal cache detection. The magnetometer section and induction balance 2 box info and projects are very interesting and enlightening! 

 

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