IDX problems

[Nupi]

Hi Koala, it seems that the reactance of your RX coil with the shield is not corect. Try to reduce the capacitor value of the RX coil until you get a better result.

[Koala]

Hi Koala, it seems that the reactance of your RX coil with the shield is not corect. Try to reduce the capacitor value of the RX coil until you get a better result.

Thanks for the suggestion Nupi might be a couple of days before I can test properly


I have something a bit wrong because at one end of the ground balance its not as bad as the other. Also the phase must be slightly out as I can't quite ground balance ferrite out nearly but its just out of range. Tried moving the null point around but it makes no difference.

not sure the hardboard I pasted the graphite onto was a good idea. The base of the hardboard is more sensitive to touch than touching the coil its self. Not sure if its the hardboard its self of the extra distance away from the shield.

Anyway air test on a silver half penny is roughly twice that of the original 8" coil but at 6.5" was slightly disappointed. Recently air tested a Golden Mask 1+ with the same coin and a 7" coil and that was 7". All ready using the LF347s I think but will double check.

[Koala]

One small observation that has no real bearing but maybe of interest. aluminum foil affects the null quite considerably but have not noticed any with the graphite. So if you are building a coil with a foil shield you would have to have it in place before nulling.

[dfbowers]

Thanks for the suggestion Nupi might be a couple of days before I can test properly


I have something a bit wrong because at one end of the ground balance its not as bad as the other. Also the phase must be slightly out as I can't quite ground balance ferrite out nearly but its just out of range. Tried moving the null point around but it makes no difference.

not sure the hardboard I pasted the graphite onto was a good idea. The base of the hardboard is more sensitive to touch than touching the coil its self. Not sure if its the hardboard its self of the extra distance away from the shield.

Anyway air test on a silver half penny is roughly twice that of the original 8" coil but at 6.5" was slightly disappointed. Recently air tested a Golden Mask 1+ with the same coin and a 7" coil and that was 7". All ready using the LF347s I think but will double check.

Yes, what Nupi said. I would substitute in additional capacitors until you can GB ferrite out around mid range of your GB pot. That might eliminate more than one issue.

[Koala]

Thanks I have taken a chance and epoxyed the TX in. Unfortunately its only 16C in the house and the epoxy needs 20 to set properly. Think it might be time for the hair dryer

[Koala]

Hope so taken a chance and epoxyed the TX in. To cold in the house for it to set properly. Might try a hair dryer

[Koala]

Still gluing it all together gave up with the hair dryer ended up with buckets of hot water on the top. No way I can get it ready for Sunday.

Lack of distance was my fault. One of the wires from the sense pot had broken off.

Still need to adjust the RX capacitor to get the correct phase but the now the Shield seems to have fixed its self ??? Can wave my hands around the coil touch the coil and the detector does not sound.


Only got the bottom half of the shied connected but seems very stable. Is there a good way to test its effectiveness

[dfbowers]

Koala. A perfect test is to swing your finished coil through wet grass.
Don.

[Koala]

Koala. A perfect test is to swing your finished coil through wet grass.
Don.

Thanks. Yep tough test. My last coil failed this that's why I am building a new one.

Wanted to test before closing up. Going to fiberglass all over when finished so no way to open it back up.


Ground balance is now sorted. Again my fault had to change the 33 cap for a 47 to get it to work then remembered I had modified the ground balance so I could use a standard Classic coil. Took the resistor I had added out and the 33 now balanced ferrite perfectly.


However the coil was working perfectly with the 33 before now its very jittery but can calm it down with the sens pot. I will not worry too much yet and try latter on maybe next door has switched something on. Also try with some fresh batteries. They still measure 10.5V under load but with the voltage drop of the diode it does not leave much of an overhead.


Distance on a cut half is superb. Getting and easy 8" up to an iffy 9" interesting its now different now the coils are glued down. Must be the slight difference on null. Before gluing it was quite a sharp cut of beep or not beep. Now its a sharp beep changing to scratchy beep for the last extra inch.

[Koala]

Not sure whats going on.

Tried some new batteries this evening no difference.

sometimes when you switch it on there is a is a constant chirping turns out its related to on position of the ground POT. Using a 20 turn less than 1 turn in either direction and the detector calms right on the point that ferrite is balanced the detector goes nuts.


Anyway have to put it back together as I am out tomorrow with it.

[Koala]

Made a bit more progress but it slow going as the epoxy is slow curing as its still only 16C in the house. Takes a day to go tacky and another day before its like a stiff plastic.


once the air gaps are fill with epoxy it became so much more stable compared to when it was tapped together





Got a spike just before each peak and trough on the RX pin 6 of U1 (pre amp output) Not sure if its just picking up the CRT oscilloscope but seems to be too regular?????

Does not seem to affect performance. Ground balance and discrimination is spot on.

[Koala]

Just given it a quick test on a lawn seems very stable. Ground balance great and does not alter when the coil hits the grass.

Discrimination is slightly different (i would say better) to my CC coil. Now an iron clad 2P makes grunt sound as you would expect with just enough discrimination to avoid a small nail/bolt but with the CC would give a good sound with way too much discrimination unless the coin was very corroded.

Not so good next to large iron guess that's because its a larger coil


There is a target in my lawn that I have not dug out. Its next to some large iron but is easy to find with the 8" however you would not find it with the 10" unless you knew where it is even then its hard to pinpoint


Might have to make a MKIII coil as it ended up a bit heavy

[Koala]

Work find on my lawn if a little heavy.

Epic fail chatters all the time manly if you hit the ground its sounds

also on some targets you get 3 beeps. One good signal became 3 beeps after I had taken the turf off. Dug it out and it was a piece of aluminum.

Back home. If I gently pat the coil nothing. If I knock the coil with my knuckles the detector sounds. However if I hit the coil with a nylon bolt the detector does not sound

[Nupi]

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

[Koala]

nylon bolt was a red herring.

it depended how far up the bolt you held it.

When in all metal mode. If I move my hand towards the coil the last mm or so there is a very slight rise it the threshold. When patting the coil this not quick enough to trigger detector to sound. How ever rapping the coil is.


putting the ground balance very negative (so ferrite makes the boing noise) stops this from triggering a sound you can be quite rough without it sounding.

So looks like I may still have a slight problem with shielding even though swinging the coil through long wet grass is fine until the coil touches the ground.