Getting ready to build the MPP

[Chet]

Hi KRinAZ, Attached is a photo of my coil. It is in an old 8” coil housing that a friend gave me. The coil form was box knifed out of foam filled art board which was lying around. It wasn't strong enough for the wire used so the windings have some BO-BOs from broken or bent sections. Even with the mistakes the principal goal was maintained by having good crossover of the wires (no parallel wires that would cause more coil capacitance). It is wound with 18 gauge Litz wire which was also available in one of my boxes of stuff.

Qiaozhi has a coil calculator at the top of the Coil Forum. Because of the zig zag pattern this coil will require some additional wire and turns to achieve the required inductance. It is easier to remove extra turns than to add if the inductance is wrong.

Air is the best dielectric for a fast coil. Sections of foam filer (tubes) used in the Chance PI Postings is a good way to stabilize the windings from bumps against rocks and bushes. Avoid using very much solid material such as epoxy or goop directly within or against the windings.

The coil works well on the bench. It will be tested outside after through experimenting and devising some kind of Ground Balance circuit. Click on the photo to expand or shrink.

[KRinAZ]

[QUOTE=Silver Dollar;197631]
That's the easy part, I still haven't figured out how to package it. I saw someone
who packed foam tubes around it then taped and glassed it to male a big donut
type housing. I cannot find the thread just now...

Found it - #30 on page 2 of the Chance PI coil thread: http://www.geotech1.com/forums/showt...-PI-coil/page2[/QUOTE] .

[KRinAZ]

I used a piece of wire 66 feet long that I had wound a mono coil with it
came out pretty close to the optimum value of 300 uh...

OK, cool, gives me a clue on wire length I need - do you remember what wire gauge & insulation it had?

.

[KRinAZ]

Have a look in this thread on how to make the form and how to wind it (look around #111);
http://www.geotech1.com/forums/showt...-PI-coil/page5

Check out post #111 you should be able to work out how to wind the coil from the pictures I posted, thanks SD.

Yes, thx much 6666!, found those a bit earlier - good that you posted those - that russian translated lacing image is pretty much the missing key.

It's still vague to me how to wire it but I'm guessing it will be clearer when I actually sit down and lace it up. Picked up Lexan today - .093" - and a 1/8" bit for my Dremel - I have an idea on an easy way to do some nice clean Lexan machining with just the Dremel and a simple jig - basically using it as a tiny router. It will cut the slots exactly the 1/8" width and terminate each slot with a round end as if I cut down to a drilled hole - but a cleaner straighter cut. Will shoot photos of course. Ultimately, if I get this basket weave thing (what's the correct term for these coils?) working, I'm going to make a full lace up set of directions and photos - kind of like the Boy Scouts knot making tutorials where they show every twist and turn making complicated knots look easy...

.

[6666]

Have a look in this thread on how to make the form and how to wind it (look around #111);
http://www.geotech1.com/forums/showt...-PI-coil/page5

Check out post #111 you should be able to work out how to wind the coil from the pictures I posted, thanks SD.

[Silver Dollar]

I used a piece of wire 66 feet long that I had wound a mono coil with it
came out pretty close to the optimum value of 300 uh...

[KRinAZ]

Have a look in this thread on how to make the form and how to wind it (look around #111);

http://www.geotech1.com/forums/showthread.php?18323-Chance-PI-coil/page5

OK, good, thx, I think I have all the info now to learn how to build one and set it up on the MPP.
I'm going to pickup lexan today and practice with string, then build it and measure it with my inductance/capacitance/resistance multimeters - then with the scope when I have a working MPP.
Thx again Silver Dollar!

That's the easy part, (the easy part, yikes!) I still haven't figured out how to package it. I saw someone
who packed foam tubes around it then taped and glassed it to male a big donut
type housing. I cannot find the thread just now...

.

[Silver Dollar]

Have a look in this thread on how to make the form and how to wind it (look around #111);

http://www.geotech1.com/forums/showthread.php?18323-Chance-PI-coil/page5

That's the easy part, I still haven't figured out how to package it. I saw someone
who packed foam tubes around it then taped and glassed it to male a big donut
type housing. I cannot find the thread just now...

[KRinAZ]

OK, update on the basket weave coil build info - I am becoming obsessed with building one of these LOL so I am putting together specific info and specifically for the MPP - when done I will put in a PDF complete with test results, measurements, etc.

I have found fragmented info on the form build and fiberglassing it. I believe I will be able to put together a layman's howto to build this for the MPP project.

The one thing that still eludes me is how specifically to wrap the wire on the form. I have found where folks have wound it wrong and had bad results, but have not found step by step of how to wind it correctly, could use some help on this...

[KRinAZ]

You can make an easy basket coil using a jig saw to cut the circle and then just drill holes.
I made this one;
[ATTACH]31435[/ATTACH]

OK, I'm in! I want to make one of these, might as well go for the "gold" and take a shot at building a nice fast self shielding coil right off!

If you have any sources of specific instructions, patterns, howto's that would be great - from what I could tell from the coil building posts, they seemed to assume someone already knows the basics of building these and knows how the form should be made, what materials are used, how to actually correctly wind it, etc.

It appears this coil is too big to fit in one of the pre-made DD coil shells, am I right on that? If so I'm guessing the most popular way to enclose it is via fiberglass work.

I did read that if someone is going to enclose it in fiberglass they use lexan for the form. I would really like to find the specifics on how to make the form, how to wind it, how to fiberglass it and include the pole mounts, etc.

I will continue searching for all this as well...

.

[KRinAZ]

I just remembered DBFlowers sells housings too. I got a couple 9" with covers off of him.https://sites.google.com/site/dbcoil...10-inch-shellsThis is one of his housings;[ATTACH]31437[/ATTACH][ATTACH]31438[/ATTACH]

Thx! - these are nice, now I know where to get one, I think the 9" would be the first one I would try

[Silver Dollar]

I just remembered DBFlowers sells housings too. I got a couple 9" with covers off of him.

https://sites.google.com/site/dbcoilshells/9-and-10-inch-shells

This is one of his housings;

[Silver Dollar]

Those housings came from Ebay, there was a guy from Bulgaria selling them there.
They were from this guy, I don't see them listed anymore though...

http://www.ebay.com/sch/mikronbg/m.html?item=111477300721&rt=nc&_trksid=p2047675.l2562

The center tapped coil allows a fast TX (as you drive only one side) and low noise on the RX
(as you use a differential preamp).

You can make an easy basket coil using a jig saw to cut the circle and then just drill holes.
I made this one;


The one shots I was talking about are the 4538's on some PI's they used 74HC221's which had
a minimum pulse width;

[KRinAZ]

...I built the coil described in the Coils Forum _ under Chance PI around Posts #110 -----126. It is a very good coil. And the 7.5-8” coil size is a good way to start, it is quieter, gets into smaller places, stays closer to the ground, and still has good depth on larger nuggets. Later I recommend that you not go above 10”, it will miss many small nuggets and is nosier and loses the other advantages of a small coil...
Hey Chet, OK, I've been reading that Chance PI coil post - I'm a bit overwhelmed at the moment, but that's a very interesting coil build (the basket weave thing) and it has the specs I will seek! I don't have the machining tools they are talking about for making the forms and such. Are they available somewhere, or did you make/machine one? Did you fiberglass yours like in the photos? I've never done fiberglass but could give it a try I guess, at least it would solve the problem of finding/making the coil housing...

.

[KRinAZ]

Hi KRinAZ,
I have completed the Minipulse Plus (rev C) kit. I am very pleased with the kit and the results.
Follow the build procedures which are very good.
Do not proceed to the next step without successful test results on the previous steps.
A few minor suggested changes; these may have already been updated in your build procedures.
Include the following parts into Step 3, Q2 (2N3904), R9 (10k) and R5 (20k)
Add to Step 7; for testing short PL3 again
Add to Step 8; for testing connect 50k Reject pot to PL3.
Thx Chet, will do on following the steps and testing/verifying each before continuing, & thx on those last 3 tips. Congrats on your MPP build!

I built the coil described in the Coils Forum _ under Chance PI around Posts #110 -----126. It is a very good coil. And the 7.5-8” coil size is a good way to start, it is quieter, gets into smaller places, stays closer to the ground, and still has good depth on larger nuggets. Later I recommend that you not go above 10”, it will miss many small nuggets and is nosier and loses the other advantages of a small coil.
Hmmm, I like the 8" coil idea - if I can get one built nice and fast I could just stick with it. Most folks I know really go for the big coils, but I seem to always like using smaller ones to get in tight spots. My bigger coils get me frustrated when I can't swing for all the rocks I bump into. My hunting grounds usually have lots of bigger rocks & boulders as well as seriously mineralized (of course lots of iron also) ground, took me a while to figure out how to run my GMT nice and smooth and quiet on this ground. & guess I'm not one who covers miles per day with their detector... I'll check out the Chance PI forum on that coil build info...

After you have it working read through the Replies to Minipulse Plus forum and try some of the recommended modifications.
Definitely will do!

.