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im using 24 awg 18 strand wire and ive cut it too short length...is it ok to re join the wire with a solder joint...will it detect the solder joint...also is graphite shielding better than scotch 24 screening tape ???
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Umm what kind of coil are you making? I have "stretched" my coil wires by soldering
on a bit more but they have been for VLF only. On a PI you generally don't want solder
in the coil especially if you went to the trouble of using Litz wire. Could it work with the
shorter wire? What indctance did you want and do you have now? -
i was making a coil but the inductance was only 140 uH as i cut the wire too short so i decided to scrap the coil shell and make another dual field coil using the same wire but because dual field coil was smaller than the coil i scraped the inductance was higher...but then the problem was making the small inner coil as i didnt have enough wire in one continuous length...so i need to solder two pieces tog ether to match the same amount of turns for both coils !!!
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Well if in doubt work with what you have. Just try to use the minimum solder possible.
If you look at commercial coils they use pcb boards, relays, caps and resistors in them.
If might not be the perfect coil but will most likely work just fine!Comment
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ok thanks
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I was thinking of getting some Litz and making a PI coil maybe I should make a
dual field? Where did you find a housing for it? The solid disk ones would look
funny I think. Also are you going to shield it?
I have a 10" coil with no shield but no working detector yet to try it out...
Also a dual field would require some damping resistors in the coil shell so a splice
in the wire wouldn't be a big deal.Comment
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ive already made a dual field coil some time ago....using a whites 12" coil cover housing.....great for pinpointing !!!! i use scotch 24 shielding but i was thinking of using graphite paint this time but not sure which is best to use !!!! no splice needed as you wind both coils separate.Comment
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The original Dual coil used a resistor after the first coil so would need to be in the housing
unless your running 4 wires back and making the connections in the PCB box.
You can put a ferrite bead over the solder joint to hide it from the coil field.
Minelab has a patent for it.
http://www.google.com/patents/US20130057286Comment
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i put the resistor in the housing but maybe better using four core cable so resistor in control box so can be changed easy or for experimenting...i could use less turns on the smaller coil and not solder but i thought large and small coil had to have the same ratio of turns...maybe i will ask about it on the forum.Comment
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Someone once wrote that a damping resistor on each winding is best so
a dual adds a damping resistor 1/2 way through the coil. It still acts like a
single coil but is better damped and has more magnetic density in the center
(of a large coil). So an 18" with 6" center coil might act like a 12" by the
small coil filling in the field...
The damping resistor is fixed once the resonant freq is determined so
seems it would be better inside the housing (but hidden by ferrite?)..Comment
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i cannot test for resonant frequency as i have no signal generator as yet....i try and do things by trial and error and see what results i get....i didnt hide my resistor with ferrite and the depth is not bad compared to a friends whites dual field...i use to think large coils say 15 - 17" were to be desired but ive come to believe that a coil about 12" with small inner coil is the best for the beach...to be honest i cannot dig deep holes so why make big coils ??? my dream machine if i could afford one would be a whites tdi pro....great depth with only 12" coil !!! to me whites the best !!!!Comment
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I'm not sure how to accuratly tune the inner coil damping resistor.
You can use a PI machine with coil to broadcast to a new coil that
is not connected to a MD to see the resonant frequency.
PI coils are somewhat like an FM antenna. Any old piece of wire will work
though a proper antenna uses 1/4 wave and a ground plane etc.
So even with a splice and nonoptimized damping as long as your finding
good stuff it doesn't matter...Comment
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Check out this thread;
http://www.geotech1.com/forums/showt...t=double+field
It says there is a trade off between depth and small target sensitivity and in general a dual doesn't
go as deep as the same size mono...Comment
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i saw a field test done with a whites tdi with a dual field coil and it was hitting US nickles down to 16" which i thought was good proformance...not sure if mono coil would go any deeper.....carl would be the one to verify this.Comment
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