Double D Coil

Hi all,
New to this board but I thought I would see what input I could get here. I'm designing my own IB metal detector and I'm looking for realistic numbers for DD coil inductance and dc resistance for the TX and RX side (Roughly 10" X 6"). I'm using these currently for simulation purposes and to set up the oscillator. I'll be running this detector @~ 7.5KHz. I'm also trying to figure out how much current to pass through the TX coil for reasonable field strength. I've found on older designs they are using nothing more than a single 2n2907 or equivalent colpitts oscillator to drive the coil. That would mean, depending on the inductance and series resistance that the AC current is +/- 100mA at best. I would have thought the current would be more, but maybe you don't need much AC current to generate a large enough field. Any thoughts or if your willing, measurements from your existing DD coil?

Thanks in advance,

Rob

Hi Rob,
I reckon you might be shakin the wrong tree as this forum usually doesn't get too technical, so if you don't get the answers you need you would be better posting on another forum but don't take offense!!!

Most the guys here want to know how to find more gold with what they have, not how to build one ,as they don't exist until proven to get gold.

If i am prooven wrong i'll wear it, but in the same token it wouldbe nice for a few of the lads to start getting a bit techo even if half of the Minelab constabulary reside on this forum

Ron

Rob I have a magazine on building all types of detectors,its an older one but has some useful info including coil construction just let me know and I'll send it.On induction balance detectors the coils are identical and mounted or tuned to have minimum induction in L2(coils are overlapped).The coil specs 32swg wound 40 turns around a 140mm dia former x 2 coils.Oscillator produces Rf bursts of 800Hz.This frequency would be targetted at larger deeper targets as a guess.To reduce current control the duty cycle,as in Pi's.
Hope this helps, Steve