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Null phase
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The picture is great - better than a foto from a normal scope I feel!!Originally posted by sdesic View Post
The USB Scope appears to be working really well.....
regards
AndyComment
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I was testing TGSL this weekend and I went to trashy area (foil, iron, pate "cans")
Tried to disc out most of that but I was unable. Mosquitoes attacked me also so I left.
Foil and iron are not so much of a problem disc is on middle position.
When I discriminate foil, what am I missing?
Some of gold stuff ... not zinc and nickel
Pate cans replaced iron bits
NemesisComment
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Discrimination Charts
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To put it in a nut shell discriminate foil and you loose silver such as pre 30s old six penny bits etcComment
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We don't have silver coins in last 70 years so ...
must stay away from trashy areas
I have another problem
I used epoxy and it shrunk coils unbalanced them
Building another pairComment
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Is there a way to reuse coil envelope which is glued with "epoxy" ?
I used strong glue in form of a silicone - corpus is ABS so no acetone.Comment
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Glueing Coils Down
We have all made this mistake!!Originally posted by sdesic View PostWe don't have silver coins in last 70 years so ...
must stay away from trashy areas
I have another problem
I used epoxy and it shrunk coils unbalanced them
Building another pair
But there is a relatively easy way to avoid it.
Roughly adjust for null.
First glue down say 50-75% of each coil. Keep scope attached while doing this. If ye if you mix too little.....if you mix too much, do not use it, simply throw it away. Mix the minimum each time or less and do it twice if you mix too little....
Let epoxy dry/harden.
Adjust for null.
Glue 50% of what is left unglued.
Let epoxy dry/harden.
Adjust for null.
Glue 50% of what is left unglued.
Let epoxy dry/harden.
Adjust for null.
And so on........
This will get you close to a perfect null adjustment I find.
I like epoxy due to it being waterproof etc., so don't give up on it too quickly....sadly it is heavy, so do not use huge amounts....
I hope this helps
Regards
AndyComment
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The one you made which shifted during potting - have u tried using it - it may be ok in use.
If u make more, dont go for an absolute null, the important factor is the phase relation between Tx and Rx signal.
When good, u can get rid of ferrite. Then you will be away ( oh and single beep not double with unclad coin )Comment
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I tried it and it is heavy and it is rejecting ferrite rod 5-6 cm
Less depth in field testing.
I adjusted sensitivity to half to remain silent.
Not very good in all metal mode - too much false signals - maybe it is my test ground.
Used disc over half to reject foil and to remain stable and silent.Comment
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Originally posted by sdesic View Post
Try small piece of graphite between the TX and RX move it around while watching the scope you might be able to re null your coilComment
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My next coil is fixed by hot glue only.
Remains on place and null.
I need to try it in field.Comment
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No matter it only has to be near. Give it a try. Hopefully you can rescue your coil.Originally posted by sdesic View PostComment
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FOR SDESIC,
only a thought you could try,
ive done it before on a coil that was a bit far out after setting,
it sounds crude, but it works,
although phase will be slightly delayed.
a copper penny on the outside of the coil shell,
on the topside, so you don't knock it off in use,
move it around whilst watching oscilloscope to get your null right,
mark the position, then superglue it !!
paint the penny black so passers by dont ask "what's the penny for !!"
works a treat, although many pure'ists would frown upon it.
LOL.Comment
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