giuhalftrack
Jr. Member
- Jul 13, 2017
- 64
- 64
- Detector(s) used
- BFO's (DIY), Tesoro Silver, Tesoro Outlaw
- Primary Interest:
- All Treasure Hunting
anyone here interested in BFO detectors ?
I started out with a Bounty Hunter BFO back in the 70s. BFO detectors can be very sensitive since the human ear is very good at hearing a slight momentary change in pitch. I remember hitting pennies at 6". I upgraded to a Compass induction balance machine. Although the Compass was easier and faster, it could not get the depth of careful BFO use. It would be interesting to design an analog machine using either phase lock loop detection or adjustable active narrow audio bandpass filtering. Another approach might be a BFO at VLF with regeneration and down conversion to audio. Keep the soldering iron hot! Ed.anyone here interested in BFO detectors ?
Got a Relco Pacesetter right here! wow! forgot I had it. Had a Bounty Hunter in the late 60s. Best hot rock (leaverite) locator ever made😋I started out with a Bounty Hunter BFO back in the 70s. BFO detectors can be very sensitive since the human ear is very good at hearing a slight momentary change in pitch. I remember hitting pennies at 6". I upgraded to a Compass induction balance machine. Although the Compass was easier and faster, it could not get the depth of careful BFO use. It would be interesting to design an analog machine using either phase lock loop detection or adjustable active narrow audio bandpass filtering. Another approach might be a BFO at VLF with regeneration and down conversion to audio. Keep the soldering iron hot! Ed.
very cool memories.I started out with a Bounty Hunter BFO back in the 70s. BFO detectors can be very sensitive since the human ear is very good at hearing a slight momentary change in pitch. I remember hitting pennies at 6". I upgraded to a Compass induction balance machine. Although the Compass was easier and faster, it could not get the depth of careful BFO use. It would be interesting to design an analog machine using either phase lock loop detection or adjustable active narrow audio bandpass filtering. Another approach might be a BFO at VLF with regeneration and down conversion to audio. Keep the soldering iron hot! Ed.
I haven't thought of it, but may also be the best choice for meteorite too. I'm not a meteorite hunter and don't know them that well, but considering the iron content and usual magnetic qualities But Still Best to use them in States without HighGot a Relco Pacesetter right here! wow! forgot I had it. Had a Bounty Hunter in the late 60s. Best hot rock (leaverite) locator ever made😋
Because BFO operates on proximity effect it will probably never equal (or even come close) to what IB can do. That said, there are some fun things you can do with BFO.Let me briefly explain what i mean... let's say that if i compare the search frequency with a set value in software (reference frequency) i don't need a stable reference oscillator so i have eliminated all the problems connect to it.
thank you Carl your post is of great inspiration to me.Because BFO operates on proximity effect it will probably never equal (or even come close) to what IB can do. That said, there are some fun things you can do with BFO.
Yes, you can use the micro to generate the reference frequency. An NCO will give you the resolution you need with the bonus that you can implement an instant retune button. You can also use an input compare/capture channel to just measure the TX frequency directly, no need to compare to anything. Of course in both case you are really comparing the TX frequency to the micro's clock.
Furthermore, you can make a VLF-BFO. You can also make an IB-BFO. You can make a multifrequency BFO. You can combine them all to make a VLF-IB-MF-GB BFO. Lots of fun things to play with. Visit the Geotech web site (geotech1.com) for more info.
thank you Carl your post is of great inspiration to me.
yes i know geotech1, I'm a member, I read a lot and post rarely, I got your book too...
I'm not looking to revive an old technology to discover some secret advantage hided by evil corporations.. I'm only an enthusiast, let's compare my interest to people that love shooting muzzle loader rifles... it doesen't make sense go hunting with those rifles but.. they like it.
Now that I think of it, I've got a Relco Pacesetter in the closet. If anyone is looking for one for their collection etc. Pm an offer.Got a Relco Pacesetter right here! wow! forgot I had it. Had a Bounty Hunter in the late 60s. Best hot rock (leaverite) locator ever made😋
On the other hand, knew an old boy that wouldn't give up his BFO even for a VLF TR machine & he'd hunt circles around us all day.
yeah build this one too... the most interesting feature was the multiplication of frequency shift. For 1Hz of frequency shift at the coil you ear 8Hz on the earphone this overcome the limitation of the human ear to distinguish small changes in the frequency (tone). the quartz reference oscillator is another improvement.best BFO i ever made was ETI 561, actualy a usefoul design with solid depth too. Very sensitive on small items, very stabile and quite useless on grass.
Shield thy coil.best BFO i ever made was ETI 561, actualy a usefoul design with solid depth too. Very sensitive on small items, very stabile and quite useless on grass.
Using a PLL frequency multiplier is how you do a VLF-BFO. Some BFOs also operate on mixer overtones, I don't recall what the ETI561 did.yeah build this one too... the most interesting feature was the multiplication of frequency shift. For 1Hz of frequency shift at the coil you ear 8Hz on the earphone this overcome the limitation of the human ear to distinguish small changes in the frequency (tone). the quartz reference oscillator is another improvement.
this is very cool. I saw your video and subscribe your channel, I hope you post more videos "in action". I made a "digital BFO" by myself too... nothing special I think it is normal that we all go to the same "idea", the possibilities offered by the MCU's really cut out many plagues of the BFO implementation.Hi This is an old thread, But I am certainly interested in BFO detectors.( I designed one, if you search for 'super-bfo backyard test' on youtube). The original idea of BFO , in its very name, is neat, as are the suggestions to further improve the power of a BFO. But let me tell you how easy and powerful a BFO can be now; As I write this, I have a microprocessor on my desk that cost 2 dollars, and It can measure the slight change in frequency of one- part-in-20 million. This chip has inside it, all the components that used to be external and had to be carefully designed back in the early 2000s, including the 20MHz oscillator and precision voltage references, so it was unimaginable back in the day when BFOs were first invented. Long-story short, if you believe 'a few transistors and some resistors' is a simple circuit. My design has basically one chip. To get technical; but as you may already know, if you have your BFO running at a frequency , say 15kHz, and you want to measure a slight change in frequency. Then the trick was to 'beat it' (mix it) with another oscillator and get a difference, an audio tone. Impressive how this was achieved with analog circuitry. Now, you can 'just measure the frequency directly', and detect when it changes by even by 0.000001 Hz. The amplification and Audio tone , can be anything you like. Hence how my design has a different beep for IRON. (Because iron increases the inductance of the coil (at close range), and non-iron conductors tend to decrease the inductance). For reference, the exact micro I'm talking about is an atmel 'ATTiny'
Drawbacks of BFO: Sensitive to the ground, 'Capacitance' and conductivity. Very touchy and noisy in general.
But, these issues can be solved.