Falcon MD20

[jladre]

For clarification, Can someone post the correct schematic and coil construction for this device?

[ODM]

A good grade probe design with modern parts would be interesting to see. The Falcon design was based on amplitude/bias change, around 300kHz, but a pitch shift would likely do just as well. Self tuning is a big help with pitchshifters and relatively easy to do with modern MCU.

Perhaps the most unique part in Falcon is what they call sensitivity ring adjustment on the ferrite cored search head, and relatively many adjustments (due to rarely seen design) for a pin point probe to dial out the sensitivity. Many pinpointers are relatively insensitive to make them more straightforward to use.

[Teleno]

A good grade probe design with modern parts would be interesting to see. The Falcon design was based on amplitude/bias change, around 300kHz, but a pitch shift would likely do just as well. Self tuning is a big help with pitchshifters and relatively easy to do with modern MCU.

Perhaps the most unique part in Falcon is what they call sensitivity ring adjustment on the ferrite cored search head, and relatively many adjustments (due to rarely seen design) for a pin point probe to dial out the sensitivity. Many pinpointers are relatively insensitive to make them more straightforward to use.

The effect of the "sensitivity ring" (high conductivity loop) is to increase the oscillator's frequency. The same efect could be achieved by tuning via varicaps or MCU-selectable capacitors. In any case, at 400K Hz the level of sensitivity (minimum acceptable freq. shift) can be decided in software and selectable via (+-) push switches.

[ODM]

I think the sensitivity ring was also called focus adjust at some point as well (by users, not the manufacturer, at least in their recent manuals). It would make sense, a shunted turn does have an effect on field shape. Something to try in a field shape analyzer program, perhaps counteracting ground "compression" that can be noticed with rising frequency, to some extent. Probably not increasing sensitivity since it's a lossy element but possibly giving better pinpoint.

[6666]

Vackar oscillator at 400 MHz (amplitude is rather constant with frequency)

What are you planning on useing for the inductor , at 400 megs it will be a hairpin.

[6666]

For clarification, Can someone post the correct schematic and coil construction for this device?

Coil info.

[jladre]

Coil info.

thanks a lot 6666!

[Teleno]

What are you planning on useing for the inductor , at 400 megs it will be a hairpin.

I meant 400 KHz, sorry. At present I'm experimenting with Murata 1415440C.

[ODM]

That copper tape for a shield probably needs to be the thinnest one you can find, or other materials. Very thin lead sheet or nickel spray. Probably still better than aluminium foil because it's easier to make a small and clean solder joint to it instead of contact joining alu foil.

A bobbin like that murata will compress the field to its sides though for probing in sand that might not be bad. One ferrite shape that could be interesting is one half of a pot core. They use such ferrite cores for some inductive proximity sensors.

[Teleno]

A bobbin like that murata will compress the field to its sides though for probing in sand that might not be bad.

Though I haven't dismanteled this bobbin it appears not to be ferrite shielded, there's ferrite on the front and in the core but not on the sides (you can feel the wires with your fingers).

[ODM]

Yep, assumed they were built as spool from the picture. For use in soft ground with a more durable probe tip (fiberglass or aramide pipe), drawing grooves into the ground, it could sense the sides of that groove while being drawn, like a very shallow plowshare.

With one half of a round pot core, cross section like an E letter, the field is focused on just one side, I would assume making it better for probing downward without pushing the probe into ground. The field might not extend as far compared to a ferrite rod, even a short range detector would probably notice the difference.

[Tim]

Hi. I think I have found a mistake in the LAY file. Lower middle pot goes direct to .01&100K(RHS),and to cathode of D2. Anode of D2 joins cathode of D1, and .01(LHS). Can anyone confirm this against schematic? Perhaps interested parties with Sprint or other could update the etch? ( I only have viewer).

[Wahyu]

my first test diy md20falcon
https://www.youtube.com/watch?v=YBfccvcAecQ

[Tim]

Great stuff Wahyu! Are you in Indonesia? Phillipines? Malaysia?. Once you fit a 555 IC with R's and cap(s) you should be able to use speaker? Also this should allow for more sensitivity. Did the wiring of the diodes on the pcb need to be changed to match the schematic, as I indicated above?
I have not made this one yet. I bought a MD20 off Ebay- it cost AUD$300 at auction(new, unused). Then last week one sold for $170(bugger!).

I hope you can translate/supply some more information here. Thank you for sharing.

[karim1980]

Please, I want a pcb+coil+Electronic parts , and everything about the device falcon md20