BFO with PI

[Kev]

Hi,
I was lying awake last night in the wee hours you know how you do, and my thoughts took me back to the first metal detector I ever made, it was a Beat Frequency Oscillator type. I have always been impressed by how well that machine worked, not so much the depth, because it was poor, but the metal/mineral discrimination. Depending upon which side of the wave you tuned it to, the frequency would go up for mineral (including ferrous) and down for non ferrous, or vise versa.

Now I began to think about how my Goldquest used to tune to a point where it seemed to beat in tune with another harmonic which made it much more sensitive although harder to listen too since the sound was tinny.

Next my thoughts led me to a point of combining the BFO principle with a PI.
Now this could be stupid but I don't know ? ?
Take a slice of the decay curve and 'beat' another synthesized signal with it, (maybe 1/t) so that they cancel each other out in air, retune after lowering to the ground with no metal under the coil, and away you go. Slight phase differences in the different metal decay curves will produce a different resultant frequency, metal/mineral dependant frequency.

Just thought I'd kick it off to see if anyone else has thought of a simple way to accomplish it.

Cheers
Kev.

 

[Eric Foster]

Hi Kev,

Many years ago a detector was produced in the UK call GROUNDHAWK. It was a combination of a PI and a BFO. You had to switch between one mode and the other, but it was quite popular with land detectorist for identifying iron. The BFO mode, obviously did not have the range of the PI mode, but it was still useful. A PI mono coil is very compatible with a BFO circuit.

Eric.

 

[UK Brian]

Last I saw of (Tony or was it Peter) Wright was when he was testing the Groundhawk with a large coil (about four feet wide) on our local treasure beach. It was suspended from shoulder straps so you stood inside the coil and your feet were the pinpoint position.
Only problem was you couldn't carry a spade or dig so a partner was needed. You also looked a bit of a ********.

 

[Eric Foster]

Hi Brian,

Perhaps this is the latest version?

Eric.

 

[Kev]

n/t

 

[jackg]

Eric,
That photo you posted of the large elip coil rigged up with plumbing pipe is just an attempt to swing a 42 inch DD on an SD minelab detector.
How do I know? because I took the Photo at our test patch and both people in the pic are my prospecting partners.
John

 

[Kev]

n/t

 

[UK Brian]

What about posting a picture of you and your 'Long Tom' 'Big Tom'? coil. See getting old, can't remember names anymore.Now that was a big coil, not like the tiddler above.

 

[Paul (Ca)]

Hi Kev,

Sort of related to your thread only in this case a BFO coil was used on one of Eric's Pi's, Mounted a garret BFO coil onto a AquaSport pi "name is close" several years ago.

Once made a deal with someone on the forum and when the AquaSport arrived the coil was bad, This person "from Fla." burned several others and then disappeared. Anyway, Mounted in a BFO coil and adjused a couple of trimmer pots on the circuit board and the Pi worked! Granted, Depth was lousy but it worked

Then Eric, Provided me with a name of company back east in "Fla." that specializes with this unit and they sold me the correct coil for a super cool price. After readjusting the trimmer pots, the unit was getting maximum depth again.

I guess BFO and Pi's do have allot in common,
HH, Paul (Ca)

 

[Kev]

Hi John,
Sorry for laughing,:blush: it was just reading Brian's post and then Eric's staright after one another cracked me up. It's certainly not a one man band is it? You'd need a cobber to dig the signals for you? Any good finds would make it all worthwhile.

Cheers
Kev