BFO "Discussion"

[Tim]

I'm pretty sure a BFO will do that. All ferrous nulled, and discernable audio difference between Ag Au and Al. Large inverted figure8 coil, or a 6 inch round/oval, depending on depth and sensitivity requirements.
Correct me if I'm wrong....

[Davor]

You are wrong.
Now that we fixed that, there are several good reasons to complicate things further from the BFO, and apart from the obvious shortcomings inherent to BFO (frequency pull, annoying constant beep, etc.).
You could have a proper discrimination even with off-resonance rig, but it did not do much with depth. The ground balance, as introduced by VLF-s was a major improvement. Motion filtering was another.

As for PI, it took over all the advancement recently, so there is a lot for VLF to pick up, and there are plenty of things just waiting.

Multi frequency is one of those. When I say multi frequency, it is not just using a single frequency at a time, but simultaneously (or sequentially) processing responses from two or more channels operating at separate frequencies. There are certain behaviours that separate targets from soil response at different frequencies, and however the approach and initial implementations seemed monstrous, with proper stimulus it is a walk in a park. The best advantage in my humble opinion is to have perfect discriminating device on a beach, and also on various difficult terrains. AND with almost no knobs to make it behave.

[Qiaozhi]

Correct me if I'm wrong....

I agree with Davor. You are most certainly wrong.
The BFO has many inherent problems, such as oscillator locking (Davor called it "frequency pulling"), constant [annoying] audio tone, poor sensitivity and depth, threshold drift, severely affected by ground mineralization, and very ineffective ferrous/non-ferrous discrimination. The bottom line is that BFOs are relegated to the very low end of the metal detector market, and are now only used in children's toys. Many attempts have been made in the past to improve the capabilities of the BFO, such as tuning the local oscillator to a harmonic of the transmitter. Unfortunately this only leads to increased stability problems. The BFO's days were numbered when TR detectors became available, and the final nail in the coffin came with the introduction of the VLF IB.

Sorry if you don't agree, but this is the reality.

[Tim]

Maybe we are talking 2 different BFO designs here. I have never persevered with any BFO remotely as useless as you suggest they all are. Are you suggesting the shielding and coil design improvements used with vlf and PI detectors have no advantage on a BFO? As for the "annoying constant beep", that it is not. It is a complex series of sounds, all of which are important, as expressed by your almighty oscilloscope. Without said "annoying constant beep" your oscilloscope would be a blank screen.
Tonight I have finished the final assembly of my IB "annoying constant beep"er, and look forward to in-ground testing in the coming days, with a view to coil improvements-to make more constant beeping.
Maybe next I will design a super high voltage detector that purposefully interferes with all other detectors for miles around, with its' "constant beeping".

Also it will be very interesting when I get my first BFO to the salt water, as despite what your experience suggests, I expect good results. Both detectors have 10 turns of external adjustment. The IB has 10 turns/100 ohms from zero up. For zero down simply switch the separate coil leads, so adjustment is on the Rx instead of Tx.
This oscillator circuit does not waver or drift. In my opinion auto ground balance has as many foibles as advantages, especially for inexperienced users. That said most PIs are useless without it.
I come into this arena with no pre-conceptions or prejudices, but I seem to be wading through them here. I really do hope my IB can perform well in-ground, and disprove some of the old wives tales held dear since the 1980s. If it's a performer, I may post the whole kit and kaboodle.
My interests lie mainly in dryland gold prospecting, so detecting small gold while ignoring ironstone is my aim. Neither my Infinium nor my GMT can do both.
Q your comments are bizarre. A BFO has total discrimination, not none. I am yet to encounter pulling or locking at all. The basic BFO I made has better detection than my gc1006 on all metal, zero discrim, and the IB is only a tad off the GMT. You all seem to be of the opinion that the laws of physics affect BFOs differently to vlf or PIs, but the laws of physics don't change. However the design is nearly infinitely variable. It is quite an advantage for me that the unwitting spread the corporate lies without first hand experience. The more people that believe PIs can discriminate, the better my chances of cleaning up after them. The more one-eyed PI operators, the less vlf operators. More ground for me. I thank the corporate masters for their greed-based oversight.

[rickb]

Troll?

Tim the troll and his posts need to be placed in his own thread so as not to pollute Davor's efforts with nonsense.

This forum has already lost to many bright individuals who now post elsewhere.
We once had a member on AVR Freaks that enjoyed posting misleading or bogus responses to questions. He was eventually banned.

Rick

[pebe]

Tim the troll and his posts need to be placed in his own thread so as not to pollute Davor's efforts with nonsense.

This forum has already lost to many bright individuals who now post elsewhere.

Rick

Can you explain why you think Tim's postings are nonsense? I, for one, would be interested to know.

[rickb]

pebe

He is derailing and taking this thread OFF TOPIC.

[bklein]

I don't understand the Arduino comment. Why suggest Arduino when you could use a ST M4 Discovery platform or the like and use DSP for much of the processing that is needed etc. I myself am not that credible with my suggestion as I am not a programmer let alone a DSP one - but I did take a look at DSP Concepts' Audioweaver and would think that perhaps this along with good programming skills (that I don't have) would be able to achieve the goals here.

[Tim]

I thought a 110khz IB WAS an LF? Again I say, correct me if I'm wrong. But don't bag me on a bunch of old wives tales. Rickb I would consider your comment to closer resemble trolling.
Rickb, I do appreciate the knowledge base here, and hopefully someone else may even learn something from stupid old me, but there is no need to turn disagreement into malice.
Do you have a monopoly here??????????
All this experimentation and tinkering here, is it relevant to metal detectors, or just to puff the chest feathers of the mathematically inclined?
So Rickb, my IB LF has no place for mention here in your opinion. Troll? Derailing? Nonsense? Of course this imbecile Tim doesn't know what he's talking about!
I mentioned my BFO because the IB is based on the same oscillator circuit.
What are you making, Rick?

[scrungy_doolittle]

The downside of low frequencies is that you lose spatial qualities as you go lower. For some it is only a binary sound that works. More options is better.
I'm on my merry way to capitulate and adopt a micro for discrimination processing part. Arduino is on top of my list.

Grin. I'm glad to hear that

The Aruino Mega is my favorite Arduino part, because it has a huge amount of I/O. These suckers (arduino's) are based on the AVR risc processor, so they are quite fast.

[scrungy_doolittle]

I thought a 110khz IB WAS an LF? Again I say, correct me if I'm wrong. But don't bag me on a bunch of old wives tales. Rickb I would consider your comment to closer resemble trolling.
Rickb, I do appreciate the knowledge base here, and hopefully someone else may even learn something from stupid old me, but there is no need to turn disagreement into malice.
Do you have a monopoly here??????????
All this experimentation and tinkering here, is it relevant to metal detectors, or just to puff the chest feathers of the mathematically inclined?
So Rickb, my IB LF has no place for mention here in your opinion. Troll? Derailing? Nonsense? Of course this imbecile Tim doesn't know what he's talking about!
I mentioned my BFO because the IB is based on the same oscillator circuit.
What are you making, Rick?

I would not consider 115 khz a low frequency. Low frequencies are generally considered in the below 20khz audio range. Pure BFO's are not good at discriminating, or anything else.
There is a difference of course, between IB and BFO even if they do use the same frequencies.

[bklein]

I don't get where you guys are going with this thread. The original focus was the suggestion of using binaural audio generation for target discrimination and localization.
The type of detecting means is not as important (to me anyway) as determining whether binaural audio would work for target discrimination in a heavy surf beach detection environment.
It would be cool if someone could make up a demo - something like this:
Make up a map on the pc screen with dots representing gold, iron, silver, copper, aluminum targets that you can place before the test. Then use the mouse as your "detector" and move over the targets while listening to the audio in your headphones. Play surf sounds on speakers. Does it work well - seem practical?
I like the idea of binaural sound but am not sure it will work. I don't get how it helps with discrimination. And if I move a coil over a target what is supposed to happen binaurally in the audio?
I'm thinking mono sound with timbre characterization would work better and be more practical. Assigning pitch to ID numbers is not good enough - analog modulation schemes may work...

[Tim]

Whatever the system, surf noise or a low hearing level of the user could be overcome with sufficient amplification. I consistently see here the old wives tale that BFOs cannot discriminate. Nothing could be further from the truth. Anyone who has actually bothered to test one would know this.
Even the metal washer/ring that fools modern vlfs will not fool a BFO.
20khz and below is Vlf. 20khz-500/1000khz could be considered LF. This is also probably fuelling this myth, and the marginalising of BFOs usefulness, as in my experience, with my oscillator circuit, the signal is sub-standard for non-ferrous until above 50khz.
I feel all of these points have been overlooked in the electronic analysis favoured by most here. Simulating a circuit does not make the result gospel. And starting with poor oscillator circuit will only ever achieve poor, or sub-optimal results. If you can design/find a good oscillator via the BFO, then that is the one to pursue.
I agree with bklein-assigning pitch to ID numbers is not good enough, and analogue modulation, although old hat, could achieve successful binaural ID.

[pebe]

See here for a definitive labeling of the various frequency bands:

https://en.wikipedia.org/wiki/Radio_spectrum#IEEE

[WM6]

..... with my oscillator circuit, the signal is sub-standard for non-ferrous until above 50khz.

.

Hi Tim, I didn't understand what you really mean with above cited sentence.

Otherwise I fully agree with you, that proper BFO design are able to distinguish between (or identification) Ferrous and Non-Ferrous (magnetic) metals.

Been able to distinguish, does not mean that BFO's are able to discriminate (filter out) different metals, this two MD features are not the same things.