Tweet
Hi everyone,
I just bought a second hand nokta IM28 coil that I want to use to build my metal detector (read ITMD, nows about electronics). I bought it because it was used in the nokta legend detector, a multifrequency machine, so I thought it was a pretty standard DD coil.
So today the coil arrived and I am reading some inductance value that I did not expect. I removed the connector in order to expose the wires and the situation is the one in IMG_A.
A: unipolar coaxial cable -> R = 42Ω, L = 5.82mH, C = 3uF;
B: bipolar coaxial cable
- Brown to black: -> R = 2.2Ω, L = 550uH, C = 10uF;
- Brown/Black to sleve -> R = 1.3Ω, L = 125uH, C = 5uF;
C: single wire without any kind of contact with the others;
Not sure if the capacitance measures have any meaning.
I think that A is the RX, B the TX and C the shield, but the behavior of the coil is weird, and i suspect that there might me some passive components inside (maybe just for nulling, like a recent thread) and that the TX is center plugged.
Why is the TX coil inductance so low? In order to oscillate it at 10kHz I should use a capacity of 330nF, but surprisingly it refuses to oscillate with C>50nF (using the oscillator at p. 75 of ITMD). Is the TX coil center plugged? These tests have been made using only brown/black wires.
Is the white wire the shield? Am I getting everything wrong??! Hope not hahah
Can you help me figure this out? Thanks!
I just bought a second hand nokta IM28 coil that I want to use to build my metal detector (read ITMD, nows about electronics). I bought it because it was used in the nokta legend detector, a multifrequency machine, so I thought it was a pretty standard DD coil.
So today the coil arrived and I am reading some inductance value that I did not expect. I removed the connector in order to expose the wires and the situation is the one in IMG_A.
A: unipolar coaxial cable -> R = 42Ω, L = 5.82mH, C = 3uF;
B: bipolar coaxial cable
- Brown to black: -> R = 2.2Ω, L = 550uH, C = 10uF;
- Brown/Black to sleve -> R = 1.3Ω, L = 125uH, C = 5uF;
C: single wire without any kind of contact with the others;
Not sure if the capacitance measures have any meaning.
I think that A is the RX, B the TX and C the shield, but the behavior of the coil is weird, and i suspect that there might me some passive components inside (maybe just for nulling, like a recent thread) and that the TX is center plugged.
Why is the TX coil inductance so low? In order to oscillate it at 10kHz I should use a capacity of 330nF, but surprisingly it refuses to oscillate with C>50nF (using the oscillator at p. 75 of ITMD). Is the TX coil center plugged? These tests have been made using only brown/black wires.
Is the white wire the shield? Am I getting everything wrong??! Hope not hahah
Can you help me figure this out? Thanks!