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Hi Guys,
Long time reader, first time poster! With the help of this site, forum and other reading on the internet I've undertaken a project to build a PI mono-coil for a minelab. The coil works and its very quiet (even in residential areas where stock minelab coils don't play nice) however the major problem with the coil is its sensitivity (or lack thereof). I'm talking about not being able to hear a 1-2oz over anything more than about 6" in air. Wondering if you can take a look at my coil spec's below and let me know if you can see anything that stands out..
Wire: 72 strand litz
Turns: 8
Coil Resistance: 0.8Ohm
Coil Inductance: 200uH
Shield Material: Home made graphite paint on surgical tape
Shield resistance: 33 Ohm/Inch
Coil/Shield spacing: 1 winding of spiral wrap
I was originally aiming for 300uH/0.5Ohm on the coil however I wasn't able to get that and there's a trade off with increasing Coil Inductance (more turns) by also increasing coil resistance. Being a novice I really didn't know which was the lesser of two evils. I was also aiming for between 50-150Ohm/Inch on the shield, in my trials it was at about 60Ohm/Inch however when I actually did the final run it was much lower.
Have I reduced sensitivity by being too low on the inductance, not having enough spacing between winding/shield or is my shield too good? If the coil is super quiet (presumably from a well working shield) does that mean it's also impeding the signal getting out as well?
Appreciate your thoughts / critique
Thanks,
James
Long time reader, first time poster! With the help of this site, forum and other reading on the internet I've undertaken a project to build a PI mono-coil for a minelab. The coil works and its very quiet (even in residential areas where stock minelab coils don't play nice) however the major problem with the coil is its sensitivity (or lack thereof). I'm talking about not being able to hear a 1-2oz over anything more than about 6" in air. Wondering if you can take a look at my coil spec's below and let me know if you can see anything that stands out..
Wire: 72 strand litz
Turns: 8
Coil Resistance: 0.8Ohm
Coil Inductance: 200uH
Shield Material: Home made graphite paint on surgical tape
Shield resistance: 33 Ohm/Inch
Coil/Shield spacing: 1 winding of spiral wrap
I was originally aiming for 300uH/0.5Ohm on the coil however I wasn't able to get that and there's a trade off with increasing Coil Inductance (more turns) by also increasing coil resistance. Being a novice I really didn't know which was the lesser of two evils. I was also aiming for between 50-150Ohm/Inch on the shield, in my trials it was at about 60Ohm/Inch however when I actually did the final run it was much lower.
Have I reduced sensitivity by being too low on the inductance, not having enough spacing between winding/shield or is my shield too good? If the coil is super quiet (presumably from a well working shield) does that mean it's also impeding the signal getting out as well?
Appreciate your thoughts / critique
Thanks,
James
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