in response to hector , silver wire has a lower resistance per meter than copper , so on resistance is lower but not by much , so for same number of turns you can have greater power or increace to the number of turns to get slightly better sensitivity / voltage deviation for same target , but is the cost worth it for the slight increace in performance ??
i have been doing allot of experimenting over the last few months , different coils , types , how many turns and seperate TX RX coils , so far , and only built a TX front end at the moment , this is some of what i have found:
results are using oscilloscope and a 3 inch square box piece of ali 3/4 inch square resting on coil:
"standard ish coil" 10inch, 30 turns 22 swg copper enamled wire , 165us on =0.25V deviation .
dual coil 10inch, TX 30 turns 22swg , RX 100 turns 30 swg copper enamaled wire wound together , 165us on =1V deviation.
but found dual coils can be quite noisy and seem to need more damping.
best result so far 12 inch, 100 turns of 0.6mm (about 22 to 24 swg) insulated wire simple bundle wrapped:
165us on = 1V deviation and 90ma av current @120hz
with 300us on time = 2.5v deviation and 200ma av current @120hz
only thing is , there doent seem to be any deviation beyond 6inch away with sample piece , so op-amped it times 100 ,
test piece is "picked up" ay 5 inches away but can't get any more distance.
so i'm doing something wrong , people are picking up small coins at 12 inch arn't they ??
the key seems to be the coil , electronics can only deal with the signal they are presented with , "they" cant "make it up" if the signal deviation isn't there then no more can be done with the electronic side of thing's.
the holy grail is the coil in my humble opinion.
using dual coils with some transformer step up increaces the deviation yes , but the distance at which a reaction starts is the same for me .
this "problem" , metal detectors in general is now praying on my mind , and that better can be done .
incidentaly , stumbled across an easy way of discrimination , on an underdamped coil that drops to 5v below top rail on it's first rebound , then oscilates for a while after, ali lifts the oscilations all together , and steel straightens out the wobbles but doesn't make them all rise as a whole.
so , i was looking for distance and stumbled accross discrimination.
ofo into a field now to look for ringpulls , might find some gold by accident.
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