finally good winding

[simonbaker]

Finally got a good winding with my coil winder using dfbowers method (glue on wire, top cover to contain coil).

Yesterday I blew it -- didn't notice one of my spacer nuts was loose and too high on one side -- made coils had square cross section on one side, thin rectangle on other. Waste of wire!

Using surfboard wax on wood to keep glue from sticking, being more careful to cover all surfaces.

Takes only a few minutes to wind.

-SB

[dfbowers]

Finally got a good winding with my coil winder using dfbowers method (glue on wire, top cover to contain coil).

Yesterday I blew it -- didn't notice one of my spacer nuts was loose and too high on one side -- made coils had square cross section on one side, thin rectangle on other. Waste of wire!

Using surfboard wax on wood to keep glue from sticking, being more careful to cover all surfaces.

Takes only a few minutes to wind.

-SB

Hey Simon,

Looks good.. What did you use for glue? I have been contemplating using epoxy instead of Spar Varnish for my next one as some others have done..

[simonbaker]

Hey Simon,

Looks good.. What did you use for glue? I have been contemplating using epoxy instead of Spar Varnish for my next one as some others have done..

I'm using this polyurethane stuff, but it takes a while to dry, holds up the works. Epoxy sounds good if you can wind fast enough.

I was thinking of good ol' resin + hardener, which is supposed to take maybe 10 minutes to an hour depending on what stuff you get.

But then I think your glue pot will harden solid, need a new one each time? Maybe paper cup makes good disposable? Polyurethane stays wet for months in the pot now with just a loose cap over over it. Also, you have to mix the resin with measured hardener, tricky for small quantities.

I'll keep looking for good, permanent, fast-drying glue.

It's probably important to use a good permanent glue, because if glue crumbles, the coil is only wrapped in tape and the coils could vibrate - maybe doesn't matter, but still...

I used to wind coils without glue or any cover on the form, then use zip-ties to bind it up every few inches (not as tidy as thread like some people, but easier). Ideally, if you could skip the taping and shielding, and instead drop the coils in a somewhat conductive (for shielding) but fluid potting that saturated the windings to stabilize them and then hardened, that would seem like a nice arrangement.

Did you experiment with graphite in your epoxy potting? Instinctively I wouldn't think it would work well because each particle might become insulated, but other similar techniques apparently work to some extent.

-SB

Looks like a few more pegs in my winder would reduce "bulges" between pegs, but they're not so bad in reality.

[simonbaker]

Tx coil

Got the TX coil wound, seems pretty good.

However, too much "varnish" got on the wire and pooled a little at the base. I could lift the coil because of wax, but could have been problem.

The weird thing is I actually modified my "glue pot" a little to try to get less varnish on the wire -- but I think I got more! Instead of running the wire over the lip of the can, I made a slot in the top and lip of the can so the wire passed through the slot -- I thought it would wipe the wire better -- but didn't I guess. Maybe back to the original way then.

So now I have two fairly good coils -- TX coil is 5.86 mH, RX coil is 6.30 mH. Amazingly, still don't know the ideal inductance relationship for the two coils, but depends on capacitors also, and they are never that accurate. But some day we should figure out what the ideal relationship for best gain without moving the phase too far.

I noticed a defect in my first (RX) coil -- some windings not glued on solidly, probably separated a little when removing coil. But they can be pressed together -- maybe with more glue. I think maybe I need to give more drying time before lifting coil so interior is really hardened.

So still learning.

-SB

[simonbaker]

foiled

Still having fun with coils.

Tried some foil tape for the first time. It is very wide, so I tried cutting a skinny strip to lay along the coil lengthwise instead of spiral wrapping, then just fold it around the coil -- seemed easier, but probably doesn't provide a "binding" effect like spiral wrapping. But the coils are glued anyway.

The 2 mil foil feels thicker than needed, but all I've got.

I had a thought - you can buy "conductive ink" for PCB repair, expensive, but I wonder how much needed to "paint" the coil?

I'd like to hear more experience with graphite mixtures also.

-SB

[simonbaker]

ferrite slug

nothing like a good ferrite slug in the morning...

[Micheal]

Is that coil gonna work with the scotch tape...i dont think so..shouldnt you have used scotch 24 farraday sheilding tape which works great.Just my opinion...or is this the wat to do it for DD coils

[simonbaker]

Is that coil gonna work with the scotch tape...i dont think so..shouldnt you have used scotch 24 farraday sheilding tape which works great.Just my opinion...or is this the wat to do it for DD coils

I don't know -- I'm using Scotch/3M Foil Tape 3311 because it is available in hardware store. It seems like heavy aluminum foil, so I imagine works about the same.

Probably much better ways to shield; I'll see how this works, although hard to know how your shield is working.

Scotch 24 Faraday sounds good though. How expensive?

Regards,

-SB

[simonbaker]

creepy

Slowly working to make a coil head out of resin same size as dfbowers shell and pot the coils in it.

Have to plan holes for cable wires and for extra jumper wires useful for testing different grounding schemes. Then think carefully because will pour the resin with coil upside down.

One problem -- my coils were formed slightly too "rounded" for nulling inside dfbowers form. So I have to squish them. But they have memory, and slowly creep back a little. So I can't null them until I bend them and leave them until they stop moving.

Always something to learn!

-SB

[dfbowers]

Slowly working to make a coil head out of resin same size as dfbowers shell and pot the coils in it.

Have to plan holes for cable wires and for extra jumper wires useful for testing different grounding schemes. Then think carefully because will pour the resin with coil upside down.

One problem -- my coils were formed slightly too "rounded" for nulling inside dfbowers form. So I have to squish them. But they have memory, and slowly creep back a little. So I can't null them until I bend them and leave them until they stop moving.

Always something to learn!

-SB

Simon,

I had the same problem with my coils.. I had to bend mine a little as well but in the long run it did not seem to cause an issue.. unless (see below).

Another problem I ran into was that by adding a shield it changed the resonance value a little.. and it's worse if the wires did not have a layer of electrical tape as the capacitance between the shield and the windings was even more. Also, I had two coils develop a short (before pouring epoxy) to the shield. It might have been the sharp edges of the copper tape or maybe I cracked the enamel while removing the coil from the form.

I was also wondering about the difference of putting the shielding on in a spiral fashion as opposed to the way you are doing it. I prefer your method but I have read arguments against it. My last two coils however have been with metalized mylar wound in a spiral.

Another thing I have learned. Make sure that the open end of the cable is plugged with hot glue or something as the epoxy can run down inside the coil and make it stiff! (school of hard knocks)..

Oh, and if you screw up a shell, I can easily send you a few more!

Looking forward to a few of your experiments with grounding schemes. I would like for someone, someday to verify or disprove my grounding methods.

Don

[simonbaker]

Simon,

I had the same problem with my coils.. I had to bend mine a little as well but in the long run it did not seem to cause an issue.. unless (see below).

Another problem I ran into was that by adding a shield it changed the resonance value a little.. and it's worse if the wires did not have a layer of electrical tape as the capacitance between the shield and the windings was even more. Also, I had two coils develop a short (before pouring epoxy) to the shield. It might have been the sharp edges of the copper tape or maybe I cracked the enamel while removing the coil from the form.

I was also wondering about the difference of putting the shielding on in a spiral fashion as opposed to the way you are doing it. I prefer your method but I have read arguments against it. My last two coils however have been with metalized mylar wound in a spiral.

Another thing I have learned. Make sure that the open end of the cable is plugged with hot glue or something as the epoxy can run down inside the coil and make it stiff! (school of hard knocks)..

Oh, and if you screw up a shell, I can easily send you a few more!

Looking forward to a few of your experiments with grounding schemes. I would like for someone, someday to verify or disprove my grounding methods.

Don

Thanks for the advice, I'll watch out for those issues.

Interesting about buffering the shield from coil -- I didn't do that. How much did the resonance change and how did you measure it?

Thanks for offer of backup shell -- may need it at some point. My first attempt will not use the shell but rather a mold I made from it and just resin. This is part of my low-tech experiments -- shell is much better way I'm sure and I'll save it for my "best" MD attempt.

Shielding is such a wildcard for me. I hope to check out the graphite I bought also. Unfortunately I'm slowing down experiments due to other stuff going on, but will keep trying.

I've still got a PCB with parts variations on it waiting to complete wiring, need to finish that. I also may replace my "SB mod" with just a smaller C9 capacitor as described in TGSL thread from now on.

My biggest problem is not having a low-noise lab to work in and test stuff. But no problem making an MD that works to 15 cm!

Regards,

-SB

[dfbowers]

Thanks for the advice, I'll watch out for those issues.

Interesting about buffering the shield from coil -- I didn't do that. How much did the resonance change and how did you measure it?

Thanks for offer of backup shell -- may need it at some point. My first attempt will not use the shell but rather a mold I made from it and just resin. This is part of my low-tech experiments -- shell is much better way I'm sure and I'll save it for my "best" MD attempt.

Shielding is such a wildcard for me. I hope to check out the graphite I bought also. Unfortunately I'm slowing down experiments due to other stuff going on, but will keep trying.

I've still got a PCB with parts variations on it waiting to complete wiring, need to finish that. I also may replace my "SB mod" with just a smaller C9 capacitor as described in TGSL thread from now on.

My biggest problem is not having a low-noise lab to work in and test stuff. But no problem making an MD that works to 15 cm!

Regards,

-SB

Yes, my experiments have slowed down a bit too.. they will certainly pick up when the weather goes foul around there and I have little else to do.

I did not measure the resonance difference.. maybe some thing to test and document, but it was just an observation that I made from making so many coils.

I may try your mod to see if it makes any perceivable difference. Little things certainly add up!!

[simonbaker]

Yes, my experiments have slowed down a bit too.. they will certainly pick up when the weather goes foul around there and I have little else to do.

I did not measure the resonance difference.. maybe some thing to test and document, but it was just an observation that I made from making so many coils.

I may try your mod to see if it makes any perceivable difference. Little things certainly add up!!

Hi Don:

Take a look at your DISC sync pulse at minimum pot setting. If it is clean, then probably no mod needed. If broken up, then I would try the C9 reduction to maybe 50 to 60 pF. But probably won't make noticeable difference!

Winter coming - a good time to hunker down and try some outlandish ideas.

-SB

[simonbaker]

it's a coil

This is my first potted coil, using latex rubber mold made from dfbowers shell and casting resin.

Resin lousy to use indoors due to very strong vapors, but it's inconvenient to null coils outdoors. However, if I do it again, I'll take scope outdoors.

I first poured a thin layer of resin to make the top of the coil head. Then I placed the coils and nulled them. Then poured second layer of resin to cover coils and make bottom of coil head.

Problem was that my mold was not quite deep enough to cover coils (or my first layer too thick), so I used plasticene to add extra "levies" (walls) to extend the mold and did a third pouring.

Results
-------

Coil head is pretty heavy. Could lighten it by drilling holes in the center piece. Feels quite strong. I plan to paint it white.

TX coil: 5.85 mH, 23.9 ohms
RX coil: 6.30 mH, 24.6 ohms

So probably not ideal inductances. But should be able to trim RX capacitor if necessary.

I have not grounded the shield to either the RX coil or the TX coil in the coil head yet, but I made three jumper wires sticking out to allow that for experiments.

Null signal at LF353 output is quite large, probably due to shield and cable capacitance. dfbowers warned me that wrapping shield directly on coil wires can do that - spacer material can help. I tried to null slightly on side of more overlap.

I connected coil to my PCB and dfbowers PCB. It does not give as good a signal as his coil, seems shorter beep and not as good depth. However, the resonances of the two coils are probably not as close together as with his coil, some C6 adjustment may help. Due to noise in my work area, can't give exact comparison.

Not really happy with it, but something to play with for now. Took all summer to make mold, collect materials, wind coils, etc. Need simpler, faster way.

-----------------
Whole bunch of pictures follow just for amusement.

Any resemblance to female anatomy is purely coincidental...

-SB

[simonbaker]

more pics

more pics...