IDX-PRO+VDI

[Koala]

Don't know what's going on. Stripped it all off and started again still the same. Giving up and starting again


I will keep the coil and try some graphite on it when I get some.

[golfnut]

If during your tests it was not potted, then I would expect it to false when touching things, as there is a small movement of the coils wrt to each other. This can give enough of a phase shift to give a valid signal.





Im trying to think of reasons for your fail...

One difference with wrapped screen is their proximity to the coil - they are generally better conductors and they are much closer to the coil so are tightly capacitively coupled to the coil.

A small change in distance of the screen wrt to the coil (a bump or shake ) can pull Rx tank or Tx tank a handful of degrees and your unit can register the change in the initial phase (null signal) as a valid phase shift and signal a false.

Some people put a couple of tape layers on the coil prior to screen this would reduce capacitive effects a little




The graphite screens are higher resistance and further away from the coils - so are less capacitively coupled to coil - so they interact with the coil a lot less. Plus when potted there is minimal movement of coil to screen - like a finished commercial coil.


The positives from your build attempt were getting 400mV at preamp out - this is very usable. Also arranging the phasing in order to reject the ground/ferrite correctly, and having good sens too!

[Koala]

If during your tests it was not potted, then I would expect it to false when touching things, as there is a small movement of the coils wrt to each other. This can give enough of a phase shift to give a valid signal.





Im trying to think of reasons for your fail...

One difference with wrapped screen is their proximity to the coil - they are generally better conductors and they are much closer to the coil so are tightly capacitively coupled to the coil.

A small change in distance of the screen wrt to the coil (a bump or shake ) can pull Rx tank or Tx tank a handful of degrees and your unit can register the change in the initial phase (null signal) as a valid phase shift and signal a false.

Some people put a couple of tape layers on the coil prior to screen this would reduce capacitive effects a little




The graphite screens are higher resistance and further away from the coils - so are less capacitively coupled to coil - so they interact with the coil a lot less. Plus when potted there is minimal movement of coil to screen - like a finished commercial coil.


The positives from your build attempt were getting 400mV at preamp out - this is very usable. Also arranging the phasing in order to reject the ground/ferrite correctly, and having good sens too!

Cheers first coil I made was fine and served me well. Hit one too many rocks on the beach with it and now either works or noisy but is epoxy in so can't be repaired.

Did tune the RX to over 40 cm on the first and this was a mistake. New build was just the standard capacitors and got 37 cm but super
stable.

Using different epoxy and possibly tape from the original. First was polyester new is epoxy.

Epoxied the new coil to a couple of strips of wood. Now the wood is sensitive to touch. It's very consistent and does not matter where you touch it. In use it behave very much like the wet grass video I watched on here awhile back.

[der_fisherman]

A few questions! and a few comments, hopefully useful....

[QUOTE=Koala;193958]Cheers first coil I made was fine and served me well. Hit one too many rocks on the beach with it and now either works or noisy
but is epoxy in so can't be repaired.
Did tune the RX to over 40 cm on the first and this was a mistake. New build was just the standard capacitors and got 37 cm but super stable.
Using different epoxy and possibly tape from the original. First was polyester new is epoxy.
Epoxied the new coil to a couple of strips of wood. Now the wood is sensitive to touch. It's very consistent and does not matter where you touch it.
In use it behave very much like the wet grass video I watched on here awhile back.[/QUOTE

If anything I write here you already knew, please ignore it, but it needs to be here for people who maybe are not as up to speed as you are....

Do you know the differences between epoxy and polyester?

Other than price, (Epoxy is more expensive), epoxy is best and will stick to almost anything if the surface is properly cleaned (except some plastics!). Do always clean and dry off well, I always use with methylated spirits (Meths) (denatured spirits in some countries) for that. It is cheap and easy to use and cleans well.

Polyester will not even properly stick to fully cured polyester!! Only when the previous coat has only just started to gel will it stick!!! On dry Polyester, it will appear to stick but can break suddenly. Whereas epoxy will stick to both fully cured and still make a good bond. (assuming clean, no dust and some mechanical roughing up for where strength is paramount - but not needed for coils!!!)

Meths helps ANY glue to make a better bond, even hot melt glue. Cleanliness is always important, clean throwaway rubber gloves are useful.....and cheap. If you get either resin on your skin, or anywhere where it should not be, if it hasn't cured, then Meths will remove it safely.

Using Meths with a toothbrush, also removes solder flux very well from DIY PCBs, especially important in sensitive circuitry. Dab dry with kitchen towels and don't let it dry "dirty". Use more Meths even after it looks clean, scrub all solder connections well, examine for cleanliness with an eyeglass or similar.....and for good soldering!!

What wood did you use? I almost always use "ply" wood (multilayer), one that is guaranteed waterproof, for boat building and the like (but I still keep it in a warm dry place for sometimes YEARS - first!) and I have never seen the effects you mentioned.....maybe yours is/was too wet and you have sealed it in? Just a thought!!

I route out a channel for each coil, which reduces the amount of resin needed and therefore the weight. When coil is nulled and fully fixed, I fill up the rest of the channel with epoxy and styrofoam for both heat insulation and weight. Caution, some glues melt styrofoam I have found, test beforehand...Then I sand down the epoxy till its flat with the plywood and then seal and paint/spray.....seal well and give at least 24 hours to harden. This gives a good looking strong coil head. Otherwise you need to buy a shell (or make one!!)

You can also route away large areas of wood, where it is not needed as the epoxy will add good strength any. Even adding some glass fibers may improve strength as well, but I have never done that. I have added thin strips of fine linen on the finished coil, before filling the rest of the channels, which also helps stiffness......glass is heavy!!

Otherwise I personally have no idea what is causing that sensitivity, but someone here will!!

Some melamine (camping for example) plates can be roughed up with sandpaper enough to get a good Epoxy bond....sadly they are sometimes a bit small for really large coils! But totally waterproof....several shapes available, one being long oval!! I have seen them used, but I have never used one myself, except for eating off!!

Any absorbent material, once dry, needs to be sealed with a good paint to stop moisture ingress. A good epoxy based paint would be best I believe in most cases, but I have usually simply used a car paint spray can.....several coats. Very cost effective and easily touched up, where epoxy paint must be mixed and goes off quickly....

When using Meths, use it outside or in a well ventilated room with no naked flames, lighted cigarettes or similar. But it is far safer say than petrol or similar as the vapor from meths rises and gets destroyed by UV from the Sun.....Petrol (Gas in the US), fills all the low lying areas and can cause dangerous explosions....

Best of luck, keep in touch

Andy

[golfnut]

you mentioned that a factory coil was perfect.


Is that coil a DD like yours?

[Koala]

you mentioned that a factory coil was perfect.


Is that coil a DD like yours?

No

I have two 8" CC one older white and one newer black coils

Neither are for the IDX so had to add a resistor to the ground POT so they would balance correctly.

The black coil deferentially punches above its weight. Tested its null awhile back can't remember exactly the figures but was only a few Mv on pin 6 but the wave form was very jagged not sine like but very stable.

Pin pointing is excellent on the factory coil very easy to be within a few mm on coin size objects. If pin pointing is not consistent the object will be something like a horseshoe. Also very good for small items like 22 cartridge cases.

Main reason for the 27DD is ground coverage the factory coil is pathetically slow going as you can only move forward 4" or so per swing.

After I get a good 27DD I would like to make a 950 copy to compare. I have a feeling it will have the edge on out and out performance in the fields around here as there is not much mineralization but a lot of iron masking due to broken plows and and horse shoes. Watched a few monte nail tests on YouTube and CC of the same size as DD seem to do better but I could be wrong.

[golfnut]

I use a NEL Hunter on my IDX 0 9x11" and covers ground well. Just about gets small silver at 6.5"

I set up for 12kHz and found a bunch of things and it generally behaves.

It doesnt like bbeing shook and not wet grass.


concentrics seem to be more stable generally. The cone shape profile in the soil I find a bit trying

[seadoggy]

My IDX Pro with 2 coil CC 22cmm and DD 27cmm

[Koala]

My IDX Pro with 2 coil CC 22cmm and DD 27cmm

[ATTACH]30656[/ATTACH][ATTACH]30657[/ATTACH]

Well done looks very professional.

Are you happy with its performance.

[Koala]

Shield

Still got problems.

Started again.

Wound a new RX and TX

Two layers of PVC tape

layer of space blanket conductive side up left gap

Wind spiral tap wire

Two layer of PVC tap

Same problem on contact with the windings.

Test okay on the bench but anything touching the PVC causes a false signal.

Shielding works as far as a charge near the coil. Unshielded blowing over the coil would cause it to false now very stable.

Have noticed that after touching the windings it takes a second to settle again.

Tried adding some extra insulation between the RX and TX no difference

Re wired the plug

Running out of ideas.

[Silver Dollar]

I never had much luck with shielding either. It usually cuts the signal way down.
Someone said the mylar might have breaks in the continuity caused by folding.
Any way to check this on your coil?

I've resigned myself to buying coils as none I have built are usable. I just got an ancient
Fisher 440 11" coil for $16 off ebay. I hope I can make it work!

I used the Tracker coil on my Bandito and have another Bounty Hunter coil for the IDX
that's going in my daughters BH JR. I'll probably try a few PI detectors as the coils for them
are easy to make!

[Koala]

SHIELD

Cheers Silver Dollar trying to get to the bottom of this.

Shielding works to a point as movement around the coil now has no effect.

Any touch of the coil causes a signal however gentle so coil is unusable over grass.

You can go to less than a mm and it's fine. Got an empty wire spool put that on the coil and the same signal when I touch it so spacing the coil will not help

Measured the working coil and its different

1-2 33ohms
1-3 22M
1-4 n/c
1-5 n/c
2-3 22M
2-4 n/c
2-5 n/c
3-4 22M
3-5 22M
4-5 3.8ohms

looks like there is some sort of resistor/s connecting the shield to both the RX and TX ?

[golfnut]

You mentioned that your original coil is falsing and you suspect it has gone bad.

New coil attempts false also.



Is it possible its something in your IDX?

[seadoggy]

Well done looks very professional.

Are you happy with its performance.

Thx .i am very happy!,only tricky part is shield Concentric coil i spend alot time to get good shield.

[Koala]

You mentioned that your original coil is falsing and you suspect it has gone bad.

New coil attempts false also.



Is it possible its something in your IDX?

I have two factory coils and they work fine. Mine you that does not necessarily mean too much as they are wired slightly different

Both of the two I have just made behave the same. Was very careful with the shield on the second one yet identical.