BFO "Discussion"

[Davor]

Thanks.

[Qiaozhi]

Matchless is a cross-breed between a BFO and IB, in a sense that it mixes Tx with another oscillator.

I beg to differ. The Matchless is actually a simple IB detector.
Please see this article by Thomas Scarborough -> http://www.geotech1.com/pages/metdet...chless150c.pdf

In the article he describes IC1a as a transmitter running at 700Hz, and IC1b as a peak detector/sine-square converter. The transistor (Q1) stage attached to the receive coil is a simple preamplifier. The Matchless is definitely not a BFO. In fact, the acronym "BFO" is not even mentioned once in the article.

I suspect you're thinking of the Beat-Balance design -> http://www.zen22142.zen.co.uk/Circui...tgear/bbmd.htm

[Carl-NC]

Interesting discussion... I will play Devil's Advocate (sorry Tim, not implying you're the Devil), but first let's argue semantics.

"BFO" describes a particular design with 2 oscillators that are mixed together to create a difference frequency that usually drives the audio. I consider BFO to belong to a class I call "frequency shift" detectors, which also include PLL, off-resonance, and loaded loop. If we expand the discussion beyond strictly BFO then things get more interesting.

"IB" strictly refers to a loop that has 2 or more inductively balanced coils, but generally has been used to refer to detector designs that have a transmitter and a receiver that quadrature-demodulates the return signal for phase info. But an ordinary PI can use an IB coil, and so could a BFO for that matter. Speaking of transmitter & receiver, we have the term "TR" that has fallen out of vogue but also once described phase discriminators, which are now usually called "VLF" detectors, whether they run at 3-30kHz or not (the Fisher 1280x and White's GMT come to mind). But PI machines are also TR machines, and a BFO could be run at a VLF frequency if you like.

Semantics aside, BFO died a rapid death in 1977 when Bounty Hunter introduced the Red Baron. Everyone jumped on the motion-VLF bandwagon and BFO development ground to a halt. Garrett hung on for a few more years producing the Master Hunter, which had really good zero-drift performance. But motion-VLF hands-down outperformed the far more mature BFO technology.

About the same time Allen Hametta was building off-resonance discriminators called A.H. Pro. Very close cousins to BFO, they really could discriminate but had poor depth. VLF killed them, too.

Interestingly, companies are still designing frequency-shift detectors. Most pinpointers, including the Garrett, use a loaded loop design in which there is a single oscillator weakly driving a coil, and targets pull the coil off-frequency which causes a rise (or fall) in a level indicator. The White's security wand uses this, too. So "frequency shift" methods aren't dead.

I'd have to guess that none of the detector companies have any plans to revisit BFO or even off-resonance. That's not to say there is nothing left to do, but that it seems a lot wiser to stick with motion-VLF and PI for now. For years I've had a concept for a radical BFO design that uses an IB coil, operates at VLF, and simultaneously runs 2 frequencies. Yup, a multifrequency BFO! Who'da thunk it? With a good microprocessor, it might even discriminate. If Q & I get around to writing a new book, I think it would be fun to include it as a novelty design. My problem is time, as in, no time to build it and get it working. If anyone would like to volunteer to build a detector that no one else has ever built before, gimme a yell.

- Carl

[Qiaozhi]

For years I've had a concept for a radical BFO design that uses an IB coil, operates at VLF, and simultaneously runs 2 frequencies. Yup, a multifrequency BFO! Who'da thunk it? With a good microprocessor, it might even discriminate. If Q & I get around to writing a new book, I think it would be fun to include it as a novelty design. My problem is time, as in, no time to build it and get it working. If anyone would like to volunteer to build a detector that no one else has ever built before, gimme a yell.

- Carl

May I suggest that you donate the design to the forum as this year's Christmas project.
Last year I gave them the MiniPulse Plus, but I have nothing planned this time.

[Carl-NC]

Might just do that.

[pebe]

I beg to differ. The Matchless is actually a simple IB detector.
Please see this article by Thomas Scarborough -> http://www.geotech1.com/pages/metdet...chless150c.pdf

In the article he describes IC1a as a transmitter running at 700Hz, and IC1b as a peak detector/sine-square converter. The transistor (Q1) stage attached to the receive coil is a simple preamplifier. The Matchless is definitely not a BFO. In fact, the acronym "BFO" is not even mentioned once in the article.

I suspect you're thinking of the Beat-Balance design -> http://www.zen22142.zen.co.uk/Circui...tgear/bbmd.htm

The Matchless is just an IB detector that senses the imbalance of the receiver coil in the presence of any metal. It has no discrimination at all, so is not even as good as a BFO.

It is a simple circuit and the setting-up of the three pots could have been made even more simple.

[Tim]

Yep, well my BFO is more sensitive than the Matchless, and my homebuild IB/beat balance more sensitive again. Could someone pleas enlighten me- will a PI find gold in virtually solid ironstone? If so, will it find the same size piece, at the same depth, that it would on quiet ground?

[WM6]

May I suggest that you donate the design to the forum as this year's Christmas project.
Last year I gave them the MiniPulse Plus, but I have nothing planned this time.

As Santa Claus project could be OK too.

[Davor]

I suspect you're thinking of the Beat-Balance design -> http://www.zen22142.zen.co.uk/Circui...tgear/bbmd.htm

Yes, you are correct, I thought of this one.

Terminology is intertwined as Carl nicely described.

IMHO it is good to know basics of all these technologies, simply because they are going to stay with us for quite some time, at least in form of pinpointers. With just about any micro, and by means of interrupts, even some much older approaches like pulse-counting FM demodulation becomes viable. So yes, Carl's discriminating pinpointer makes sense.

[Tim]

My opinions of re-invention via new technology, and the basic principle that not all stones have been overturned has been shouted down here. Please, experts, don't bag us amatuers so easily. There may be some gold amongst the ideas you so easily dismiss.

Could someone please answer my question regarding detecting gold through solid ironstone, or will this mean some will have to eat their words?
As I have at least a small amount of humility, I won't mind if that someone is me.

[Gwil]

I'd like to know whether any type of detector can find gold through solid ironstone. It sounds pretty difficult to me, but there is no ironstone (or gold!) in my part of the world so I have no personal experience.

[Tim]

YEP! All quiet here. Squeak, squeak. Not even a mouse. God forbid if there is a place for non-PI technologies.

[Tim]

YAY! Gwil, old mate. My IB and BFO will both see a 1c copper coin through a set of fencing pliers. But apparently that has no bearing on this question?????????????? Because, apparently it is IRRELEVANT.. to what I don't know, maybe it's irrelevant to having an oscilloscope. HAHAHAHAHA!
Maybe Whites, Fishers and Minelab just don't want us to know something?

[WM6]

It sounds pretty difficult to me, but there is no ironstone (or gold!) in my part of the world so I have no personal experience.

The same, no personal experience regarding Tim question. So I can only guess what is possible or not.
I have a lot of ironstones (abandoned iron mine near to me), but not trace of solid gold in it, till yet.
But if I put 1.1gr gold nugget under about 4-5cm thick piece of ironstone, I can detect it, using some (prospecting p.a.) detectors.

[Tim]

Thanks WM6. Is that a PI or vlf or other? The original vehement disagreeance , which resulted in my LF discussion being drafted, followed by the deafening silence leaves me with no doubt some corporate disinformation is afoot. There is no capitalism available when a few cents worth of components can be snotted together by anyone, and perform on ground where derivatives of a specific fail.
Tick, tick, tick. I eagerly await the responses. Don't you DARE call this trolling, mods.