IDX problems

[Koala]

Help shielding is driving me mad


I have built a new 27cm DD coil


Made the shield with graphite and yacht varnish. One side came out at 100 ohms per square in the other is 500


no mater how I connect the shield I can not make the coil stable.


Even touching the coil cable makes the detector sound of even if its near the control box.


so I disconnected the shield from the cable and and placed a separate wire to the connector. A slight touch of the original data cable still make the detector sound off as does touching anywhere on the coil underneath or on top makes no difference.

touching the new ground wire and the detector does not sound even if its the bare wire

A factory coil works fine

Tried USB2 cable and high quality microphone cable.

tried top and bottom shield only to ground pin on connector

tried top and bottom shield plus RX earth to ground pin on connector

on the connector side I have tried just the ground pin and the ground pin and connector shell

Must be missing something simple

Other than that the coil is working great as I have nearly twice the detection range on a silver cut half over the factory 8"

[6666]

Picture ?

[sinclairuser]

hi Koala, i could not get graphite shields to work on the vlf coils i have wound, they behaved as if no shield was fitted, the two completed dd coils i made have alu foil 6" coil and copper foil 9" coil,
the 6"coil has a simple foil wrap(really thin wrapping foil), applied on top of thick self amalgamating tape to give some distance from the wire,
the larger coil was done the same way except i used some thin copper foil (non adhesive) i got from the craft dept in the "range".
the copper foil is best since its 1/2 an inch wide on a spool so its easy to wind, it also takes a solder tag wire, the alu foil was a nighmare it kept breaking, i used conductive glue to add the tap wire.
check craft shops and suppliers for "fine copper ribbon", it was £6.00 for 15 meters and will make a few coils.
aly.

[Koala]

Picture ?

not much to show with a photo as the shield is now covered in two mm of foam

[Koala]

hi Koala, i could not get graphite shields to work on the vlf coils i have wound, they behaved as if no shield was fitted, the two completed dd coils i made have alu foil 6" coil and copper foil 9" coil,
the 6"coil has a simple foil wrap(really thin wrapping foil), applied on top of thick self amalgamating tape to give some distance from the wire,
the larger coil was done the same way except i used some thin copper foil (non adhesive) i got from the craft dept in the "range".
the copper foil is best since its 1/2 an inch wide on a spool so its easy to wind, it also takes a solder tag wire, the alu foil was a nighmare it kept breaking, i used conductive glue to add the tap wire.
check craft shops and suppliers for "fine copper ribbon", it was £6.00 for 15 meters and will make a few coils.
aly.

[ATTACH]32684[/ATTACH]

oops have some copper slug tape but the RX coil is glues to the base.

[Koala]

thought i would do I quick and dirty test with a sheet of aluminum kitchen foil. At first I thought everything was okay but then realiszed that when the foil is near the coil the null alters. After readjusting is just constantly chirps away.

With the foil shield or original graphite shield or both the coil is unstable even blowing the air above the coil is enough to make it sound.

[dfbowers]

Just an observation I made with a couple of my builds in regards to stability. When using LF347s instead of LM324s for U3, it turns my IDX into a really hot machine.
If I set my GB control too low I can cause instability even with stock coils. Just rocking my coils ever so slightly causes false signals. Setting by GB control at or close to where ferrite slugs are rejected, my IDX is stable and causes no issues at all.
Don

[golfnut]

If you get really good sens, I guess there is something else going on.

It may be you Rx coils is actually resonating with your Tx.

This makes unusable jumpy machines with probs like your one.


Try detuning the Rx coil /cap with an additional 2n2 to pull it down a bit and have a test

[Koala]

Just an observation I made with a couple of my builds in regards to stability. When using LF347s instead of LM324s for U3, it turns my IDX into a really hot machine.
If I set my GB control too low I can cause instability even with stock coils. Just rocking my coils ever so slightly causes false signals. Setting by GB control at or close to where ferrite slugs are rejected, my IDX is stable and causes no issues at all.
Don

Good idea. Had already adjusted to ferrite to test but adjusting does make a slight difference to the constant chirping. However at no setting is the coil close to stable.

[Koala]

Don't know if this will help.

Noticed this but forgot to mention in original post.


Coil is on a wooden stool. If I touch the stool the detector sounds. As I let go there is a series of about 8 decending in volume chirps about 1/2 second very consistent happens every time

[Koala]

If you get really good sens, I guess there is something else going on.

It may be you Rx coils is actually resonating with your Tx.

This makes unusable jumpy machines with probs like your one.


Try detuning the Rx coil /cap with an additional 2n2 to pull it down a bit and have a test

Tried unfortunately did not help. Also loss the ability to reject ferrite. Tried readjusting the null but could not get the phase correct did not spend that long though as the original problem was still there

[Koala]

Going to spend some time getting this coil 100% as I have a day digging planed next Sunday and would really like to use it because of its extra depth and ground coverage over my stock coil.

don't know what next to try though

[Koala]

Had a quick check of an original coil connector. RX and TX pins show resistance as expected Shield and coil connector shell are connected together and no other readings so does not look like anything funny is going on inside the coil.

[Koala]

Still no idea whats going on but some magic has happened.

Taken the extra 2n2 off. Soldered the original shield back. Still good distance. But its working much better

Now if I touch the wooden stool nothing. Blowing over the coil nothing. Still slightly sensitive to the coil being touched.

Don't know why ? Been apart and back together dozens of times





100% sorted out the cable being sensitive touch. Must have some ground loop problem. If I jump a cable from the ground pin to the detectors metal case its fine. Even though I have continuity between the case connector and pin. Not sure what the permanent solution will be might try taking the connect off the case and clean everything back up for a better contact.
Even though is should not be a problem as a factory coil works fine.

[Koala]

Can't epoxy the TX winding down till I understand this instability. At the moment it is working fine except the phase is too far out to ground balance. With the ground balance at one end of its travel coil is okay ish. At the other end the detector is very unstable and detects my hand, breath and touching anything near the coil.