IDX-PRO+VDI

[Silver Dollar]

Well all the factory coils I have seen use graphite to shield. It forms a resistive barrier
as opposed to a conductive one. So it drains the charge better. The idea with a conductive
one is to show the coil a uniform capacitance so external changes are not seen.

Others seem to have had no problem with conductive shields. I have a coil I made with al foil
shield but haven't been able to make it stable.

The factory Tesoso's seem to tie the Shield to TX minus although on my new Deep Search it is
totally seperate. How do you have the grounds in your coil wired?

It looks like 22m is the coupling from shield to ground in that coil, maybe try a 20 meg resistor
from shield to ground? It might drain the charge and act like resistive shielding?

[Koala]

The factory Tesoso's seem to tie the Shield to TX minus although on my new Deep Search it is
totally seperate. How do you have the grounds in your coil wired?

Tried every combination I can think of

Would like to know how others have succeeded

[der_fisherman]

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.

Exactly how did you connect the grounds and where?

[Koala]

Tried both the TX and RX just to the cable shield
Tried both the TX and RX to both the earth side of the RX and the cable shield (Exactly the same)

at the connector end I have tried both with and without the connector shell connected (original has cable shield to connector shield)


In all metal mode it depends which part of the coil is touched as to weather the threshold goes up or down.

[der_fisherman]

Tried both the TX and RX just to the cable shield
Tried both the TX and RX to both the earth side of the RX and the cable shield (Exactly the same)

at the connector end I have tried both with and without the connector shell connected (original has cable shield to connector shield)


In all metal mode it depends which part of the coil is touched as to weather the threshold goes up or down.

Did you try running both shields to the electronics (no short between them and not connected to the coils) and connecting them at the correct point(s) on your PCB. believe that was the advice from someone on either TGSL or IGSL at some point. I also used it on several home builds made over the years. HiFi systems use the same method to increase stability and reduce interference. One central earthing point....
Also, the width of the "gap" is important, I use about 1 cm, but I am far from being an expert on this point and I would refer you to the experts here.....not me!!
There is somewhere here an excellent .pdf from dbowers, that is well worth reading for any VLF build of "D" coils....but could not find it anywhere, but someone will know exactly where it can be found. Read that fully, both parts I & II....You will love it.....Look here:-
http://www.geotech1.com/forums/showt...light=tgsl+101
regards
Andy

[Koala]

Cheers

Only using 4 core cable with screen. People have had success using USB2 cable which does not have enough cores for separate earths ?

Getting somewhere but don't know where.

Disconnected the shield at the coil and there is no noticeable difference looks like it could be a cable connection fault

With no coil installed you can touch the metal case and threshold does not alter. Same with factory coil.
But when I install my coil threshold changes if I touch the metal case or the headphone cable.


Not 100% sure how the cable connector should be connected check the original but it's been potted.

[Silver Dollar]

My guess is your Mylar is discontinuous. Any part that is not connected to the drain wire will act
as a cap and pick up noise. Try wrapping kitchen foil around the outside of the coil temporarily
and ground that. If it solves your problem the mylar is the fault...

[golfnut]

Ive done this foil trick in emc work in test houses for radiated sprious emissions for some well known brands,

it just lets u rule stuff out quick

[der_fisherman]

Cheers

Only using 4 core cable with screen. People have had success using USB2 cable which does not have enough cores for separate earths ?
Getting somewhere but don't know where.
Disconnected the shield at the coil and there is no noticeable difference looks like it could be a cable connection fault
With no coil installed you can touch the metal case and threshold does not alter. Same with factory coil.
But when I install my coil threshold changes if I touch the metal case or the headphone cable.
Not 100% sure how the cable connector should be connected check the original but it's been potted.

I personally use only 2 core cable with shield, one cable per coil......shields connected to the central earthing point on the PCB, nowhere else.....but thats just me.

I have never ever attempted to use USB cable as some are of very poor quality I am told....

Hopefully one of the experts will chime in with some good information....that info about mylar is very interesting and possibly helpful. How did you connect the mylar to the cable shield? Did you measure at the break point that it was continuous, using an Ohmmeter?

regards

Andy

[golfnut]

When stuff is that lively it can be things oscillating, out of band. It could be daft stuff like the audio amp oscillating at low RF.

[Koala]

I personally use only 2 core cable with shield, one cable per coil......shields connected to the central earthing point on the PCB, nowhere else.....but thats just me.

I have never ever attempted to use USB cable as some are of very poor quality I am told....

Hopefully one of the experts will chime in with some good information....that info about mylar is very interesting and possibly helpful. How did you connect the mylar to the cable shield? Did you measure at the break point that it was continuous, using an Ohmmeter?

regards

Andy

Tried USB2 (branded) but now on good quality mic cable at the moment. Known to work according to MD4U.RU forum

Even without the tap wire it is continuous using an multi meter

Tried only connecting to one point. Difference could be that I am using a metal box that's grounded (technically - rail) to the PCB POTs and connector. Maybe I need to insulate the coil connector however the factory coil works fine

Looking forward to sorting this but out all today detecting.

[Koala]

My guess is your Mylar is discontinuous. Any part that is not connected to the drain wire will act
as a cap and pick up noise. Try wrapping kitchen foil around the outside of the coil temporarily
and ground that. If it solves your problem the mylar is the fault...

Nice and quick test. I will do this first but out all day today will post results.

[Koala]

When stuff is that lively it can be things oscillating, out of band. It could be daft stuff like the audio amp oscillating at low RF.

See what your saying. But seeing as I have two coils here that work properly I am guessing the problems I am having are my own doing with my homemade coils. Would like to know how the factory coil is wired as there is high ohms between both TX and TX and shield and the connector is also connected the the shield (is that just a short from the shield pin or separate in the coil end)

[der_fisherman]

See what your saying. But seeing as I have two coils here that work properly I am guessing the problems I am having are my own doing with my homemade coils. Would like to know how the factory coil is wired as there is high ohms between both TX and TX and shield and the connector is also connected the the shield (is that just a short from the shield pin or separate in the coil end)

High ohms between the two shields is exactly what is usually needed (though what you wrote is a little ambiguous!). Then they will be "linked" to that central earthing point ONLY when plugged into the control unit. (assuming that I correctly understood your post!)

If your search head has low ohms between the two when not plugged in, you have probably found your problem(s)....
Generally speaking:-
There should be no contact between either coil and either shield.
There should be no contact between shields in the search head, though they may be linked in the plug. If so, you will need to separate them before measuring.
There should be no "loops" anywhere, that is, no link say between shields at the search head and the plug or control unit.
There should be no links in the head between the coils.

Some professional search heads have caps in them, which must be taken into account when using on your own control unit.....I am not clever enough in this to have a personal opinion with any validity on this point....sorry.

regards

Andy

[Silver Dollar]

My homemades show lots of noise. One has center tapped RX and no shield, the other
Has metal screening as a shield. My original Tesoro brown coil works great and is wired like this;


The 2 shields are connected and used as the TX minus. RX minus is tied to shield in the coil housing.
Some say this isn't the best configuration.

My Deep Search is a bit different. The RX is center tapped (center point goes to TX minus) and the
shield is totally separate.


I have tried different wiring schemes too on my homemades and haven't gotten satisfactory results jet.

The Deep Search has weak volume. It responds similar to the Brown one (strong volume at close range)
but just sounds smaller. I was looking for the volume control on the other coil to turn it down and on this
to turn it up. Not really sure what causes that it seems to be duty cycle of the audio??