DUAL FIELD QUESTION

[daverave]

does a dual field coil have to have the same amount of turns for the large and small coil ???

[Carl-NC]

In most cases you can get away with pretty much whatever you like as long as they are damped properly. You can try equal turns or equal inductance (inner coil has 1.4x the turns of outer). I don't recall how they are split in the SMPI and TDI. I do think there is an optimal split that the stock TDI coil did not achieve because it had worse ground pickup in Australia than a straight mono, so TDI-Oz units ship with a mono. But it's not been a problem except there.

[daverave]

i scraped my other coil with the 140 uH inductance and used the same wire to try and make a dual field coil being a 12" coil the wire was enough for the larger coil...but i could not match the turns ratio cause to complete the small coil ive had to use two lengths of wire joined together...but total inductance is good at around 280uH...but im worried about joining two lengths of wire with solder cause i read somewhere on the forum that the coils can detect the small solder joint...so not sure how to proceed ????

[Carl-NC]

The solder joint does create eddies but it's a static target (moves along with the coil) so effectively it gets ignored. Don't worry about it.

[daverave]

thanks carl.

[daverave]

ive just started damping the dual field coil and im a bit confused...i used the damping setup as bb sailour recomended...i was able to damp the 12" coil at around 700 ohms...but the small coil would not damp using the bb sailour setup so i tried a 1k power potentiometer and smaller coil damped at 50 ohm !!! is this correct or have i made an error ????

[Carl-NC]

I don't know what BB recommended, but 50 ohms is quite low. Something's wrong.

[daverave]

i will have to double check it...the other problem is that the delay is only around about 5us....and i cant see that working with salt water beach without ground effect.

[Carl-NC]

5us is incredibly aggressive. 12-15us is about as low as you can go in salt water.

[daverave]

not sure how to get around this 5 us problem ???

[Carl-NC]

Define the problem...