BFO Coil Works For PI Detector?

[GB_Amateur]

I recently bought (from Steve) a White's Sierra Pulse Pro (SPP) PI detector which is effectively a TDI/SL without a delay adjust (locked at 10 microseconds) and without a conductivity switch (locked in the 'All' position).  When I took it down to the creek with the Minor John 5in X 9 in folded mono coil I was disappointed when it floated.  Apparently most coils are either for dry land use (thus lightweight) or for underwater use (heavy).  I've been spoiled by my Fisher Gold Bug Pro 5 inch round DD which exhibits (by design, I'm confident) neutral buoyancy, meaning it neither sinks nor floats when placed under water.

Besides the three coils that Steve included in the sale I now have a fourth -- a 3.5 in X 7 in White's coil, which I understand was an early (prototype?) version no longer available.  Unfortunately it joins the 5x9 Miner John, the White's 12 inch "Mono Aussie", and White's Super Pulse 150 (mm diameter mono) as floating searchcoils.  Of these four only the 12 inch Mono has an open structure.  There are other coils available from White's and from Razorback (Miner John) but they don't seem to advertise whether or not they float, sink, or are neutral buoyant.   Furthermore, as those of you who own PI detectors know, they aren't cheap, so buying with the hope that they will work well in water seems like a costly hypothesis.

I had an idea, which seems crazy, but then occasionally crazy ideas work out.  I have a Garrett BFO Master Hunter detector I bought as a backup (for a Garrett's Groundhog 15 kHz VLF/TR) back in 1979.  BTW, it still works.  I also read in Charles Garrett's 1985 "The Advanced Handbook on MODERN METAL DETECTORS"

[GB_Amateur]

(sorry, hit the wrong key)  ... that the PI and BFO share the property that they both have a searchcoil that shares one loop for both sending and receiving.

So, you might now guess what I'm thinking.  Could I mate the Garrett BFO coil (which is neutral buoyant) to my White's SPP/TDI?  Yeh, I know, "you'll shoot your eye out, kid!".

 

[DDancer]

Adapt it and give it a go. No harm. Well a little... PI coils are made from a different wire type with different insulation requirements as well as a bunch of other LCR stuff. But hey might be intersting. Otherwise a sand bag works for bouyancy.  Not shooting your eye out :) just playing with fire. Hehh.  Let us know eh?

[Ridge Runner]

GB

I too have a SPP and I find it's a good PI detector. My question is don't you have enough coils with it ? If you see a puff of smoke it will too late but it's your cat and you can skin it like you want.

Chuck

[Steve Herschbach]

You do have a lot of remaining warranty but that would be a one way to void it. Not a good idea. Contact Miner John for a recommendation - he might even custom make a coil for you. You might also try looking for a used Coiltek Platypus coil. Finally, there is the old sock full of sand tied to top of coil trick.

[Hard Prospector]

With PI's, the coils are very specific to the electronics and tuning (including the length of wire from loop to control box) 

Your creating a "zombie PI", I wouldn't go there. BTW, I would keep any TDI  far away from water. Even a quick dunk and its done.

[RickUK]

Why go to all that complicated trouble to adapt something that probably would not work,K.I.S.S keep it simple stupid.

Anderson shafts do a Whites Coil Weight that should cure the problem.

The Anderson Coil Weight is designed to fit the Whites Dual Field and Beach Hunter 12” (300mm) Coil. The Coil Weight will help reduce buoyancy issues common to these coils. Coil Weights are made from an all natural material coated with a yellow poly finish. Comes with instructions and mounting ties.

 

Coil Weight

Although i have never used one that should sort your coil floating problem out

[Roughwater]

 

You could use a multimeter that reads inductance and read across the pins on the connector of a good coil and compare it to the same pins of the connector of the coil you want to use.  Check the resistance as well.  

It's been a few years but I made a few coils for a Whites TDI detector.  They were mono coils and actually worked pretty well.  Part of the design requires that you make enough wraps to give you a specific Inductance.  It think it's around .300 mh but doesn't have be exactly .300. Unless you have some electronics background it may not be something you want to do. You can get a usable meter for between 30 to 50 dollars.  Probably much cheaper and simpler to just buy the coil weight or go with sand in the sock.  

The attached pic is a partially built coil i made.  Not a lot to one, at least not to a mono coil. After getting the coil to the point that you see in the picture, put a thin plastic wrap around it and another wrap of fine mesh for shielding, a little soldering, stick it in a coil frame and your done for the most part.  

 

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[Roughwater]

Pic of same coil nearly completed.  As you can see, not a lot to a mono coil but still takes a number of hours to build one by hand.

 

[Roughwater]

TDI with home made coil attached.