IDX problems

[Koala]

Do you know what the resonance frequency of the RX and the TX coil is, with the shield ?

Short answer don't know
However

Pretty sure my windings are close to the original spec on the IDX thread

TX wire from 0.70 to 35 laps - 0.587 mH - within 1 mF capacitor
RX wire from 0.15 to 270 laps - 35.6 mH - 0033 mF condenser inside

With the correct capacitor on the TX and RX with or without shield measures the TX oscillator at 6.5Khz measured on a oscilloscope.

Phase between the TX and RX must also be close as the detector will ground balance fine

[Koala]

Mmmm triple beep sorted. 8" coil works fine new coil fine on a copper penny but gives a triple beep and a silver cut half penny. New batteries did not last long (Only done less than 16 hours normally does near 40) measures 9.6V in circuit which is normally fine. However when I put new batteries in I get nice strong single beep to 8" on the cut half(which is more than before?).


Can make it work in several ways. Reduce sensitivity. Turn down threshold. Or make the ground balance very negative. All have an affect on depth

As it only seems to fail over the last few MM

I have changed coil to a MKII and a 1/2 LOL and now even heavier by fiber glassing a foam spacer under the coil

Have to go out detecting to test as it works find on my flat lawn even if the grass is wet


When building a new coil are spaces important and if so where and how big. coil to shield? shield to outer shell?

what resistance are we looking for when making a graphite shield

[Koala]

Been doing some testing. Still not 100% happy

Place a worn copper penny 10" down under the lawn. Get a tone swinging way above the ground but only get a really nice tone if the disc is at zero. At this setting most iron is accepted. Makes no difference where the ground balance or threshold is set.

Setting the ground balance very negative and quite a long way below ferrite seems to have very little if any difference on depth but the coil appears to be much more stable although the real test will be in a field.

Air test. Get a nicer tone near its maximum depth if I turn the threshold down slightly but means pinpoint mode no longer works unless you turn it back up. If threshold is at its optimum level for pinpoint mode the last inch of depth is loader but broken tone and you probably not dig it.

Finally new problem. With both homemade or factory coil installed if I touch the metal box of the detector it sounds. At the moment I have the boards outer edge to the box connected and the metal case of the POTs connected

Anyone know the answer to

When building a new coil are spaces important and if so where and how big. coil to shield? shield to outer shell?

what resistance are we looking for when making a graphite shield

[Nupi]

Maybe you could suffer from a harmonic frequency or a oscillation?

[Koala]

Thanks Nupi not sure whats going on.

Need to get in the real fields soon for a proper test. The flat lawn is a bit of a cheat.


Found one fact from all this testing. In disc mode with the disc at it's minimum the distance on a cut half is 9" With just enough disc to make a small rusty bold make a crack sound if swung across the short side but still sound okay if swung down it's length. Distance is reduced to 6". A sliver six penny it does not make much difference if the coin is flat to the coil but if the coin is on it's edge then distance is roughly halved with the disc turned up and with enough disc to fully block the small bolt the coin is almost undetectable on it's edge.

[Koala]

Frustrated now.

Had an idea though maybe some kind of static buildup in the resin I used. thought I would test with by placing some conductive paper tapped over the coil.

Reset the threshold. Reset the ground balance to ferrite.

Can't test it because it's fixed it's self.

No idea why. Not changed anything as far as I can remember. I have taken top of the box. Added some hot glue inside the coil connector and plugged the headphones in and out.

[Nupi]

It could be that the spirit of Murphy inhabited in your home with you now???

Get the hell out of here!!!!

[Koala]

Ahh its back.

Looks like a GND loop type problem and not a shield problem

If I disconnect the coil connector locking ring it's fine connect it back up and it fails again very consistent at the moment. Time for some more test. At least if it remains consistent it should be easy to beat

[Qiaozhi]

Ahh its back.

Looks like a GND loop type problem and not a shield problem

If I disconnect the coil connector locking ring it's fine connect it back up and it fails again very consistent at the moment. Time for some more test. At least if it remains consistent it should be easy to beat

If the coil connector has a metal body, then you need to make sure it's connected to the shield ground.

[Koala]

If the coil connector has a metal body, then you need to make sure it's connected to the shield ground.

Cheers


using 4 core cable

The shield is connected to the outer shield of the cable at the coil end


At the connector end it is connected to both the connector and the GND pin which as far as I can tell is the same an an original coil.


Have check something is not amiss in the connector as if I unbolt the connector from detector and have it floating in the air its also fine


Looks like this one sorted and just need a bit of fine tuning.

Thanks everyone.

[Koala]

For the life of me I can't see what I have done wrong. No big deal as if I isolate the metal detectors connector from the metal box it works fine if I pull the metal locking ring back it works fine.

Factory coil works fine as it is though. Opened the factory coil connector shield is only connected to one pin and to the connector shell. Same as mine. Can't tell if 5 core has been used as its covered in hot glue

[golfnut]

It may be a ground loop?

Good practise is to pick a single common ground spot and bond all relvant grounds to that chosen point.

[Koala]

Finally got out to give the coil a proper test. Unfortunately there was not much to be found in those fields. They were quite a noisy fields and full of rubble on the top and hard clay underneath.

Coil did not preform as well as expected.

With the machine ground balanced there is a lot of false signals mainly from any small rise in the surface of the ground.

Also the coil is not kept perfectly flat to the ground then the detector sounds.

Raising the coil a inch or more of the ground and ground balance set far too positive made the detector usable but it was still slightly unstable

Strong signals are not a problem as I can still pick them out from the back ground noise. However must be missing lots of the weaker signals.

Did mange to pick up a two shilling coin one of only a handful of coins from the day. Depth is also good pulled out the top of an aluminum can from over two foot down took some digging out in the clay next time is will be a bronze age axehead.

Have to play around with the settings some more and try in some different fields. Still not quite 100% happy with the coil but its the best I have made yet.

[Koala]

Been awhile but I have now had a play with the coil.

Ground balance metal detector and set of swinging across the field

Wet grass was not a problem so think my shield is fine

Get loads of falsing. Bumping the ground, clump of grass or tilting of coil would all cause it to sound off


Found that if I turn the ground balance much more positive and the coil quietens down lovely and don't seem to loose too much if any depth in the ground. Still picks up a Victorian penny at well over 12" in my lawn.


Still need to learn the coil as it behaves quite different to the stock 8". Mainly the double and treble beeps which are quite common with this coil.

Some shallow coins flat to the surface give a double beep but if I lift the coil it changes to a single.

But also some coins on edge give a double beep one direction but not if swung at 90 and some long thin iron does the same thing ?????

Do the same lift coil trick as before and both the iron and the coin on edge turn from a beep to a grunt. Need to get some more hours in digging both sure I will learn the difference Maybe thumb the discrimination up a bit over these louder shallower targets.


Looks like its a keeper. Need to get over some nice ground for a proper test. Strange how much more positive the ground balance needs to be over the stock coil but guess that's due to so much more signal coming back.

[golfnut]

good sens on the vic penny,

the double on close pass is the target signal phase plus the Tx or Rx coil detuning minutely introducing enough of a phase shift to give another bang.

If u put a det over say a radiator, the Tx shifts by tens of Hz!