Double D Coil Question

[Shakin97]

Does anyone know any "standard" used for building the Double D coil for a IB detector? Let's assume about a 10" coil. I'll be using 24awg enameled wire for construction. What I'm looking for is what inductance and resistance is typically found on Double D coils on both the TX and RX on coils roughly this size. My best guess from what I've read is about 1mH TX and about 400uH RX??? I'm building my colpits oscillator and am targeting 15KHz but it is hard to figure out what the capacitance values are if you don't know the inductance.
Another question I would have is does anyone know roughly what the current levels are used in these coils? Is it just limited by battery life or concern about saturating the receiver?

Thanks!
Rob

[mikebg]

Does anyone know any "standard" used for building the Double D coil for a IB detector? Let's assume about a 10" coil. I'll be using 24awg enameled wire for construction. What I'm looking for is what inductance and resistance is typically found on Double D coils on both the TX and RX on coils roughly this size. My best guess from what I've read is about 1mH TX and about 400uH RX??? I'm building my colpits oscillator and am targeting 15KHz but it is hard to figure out what the capacitance values are if you don't know the inductance.
Another question I would have is does anyone know roughly what the current levels are used in these coils? Is it just limited by battery life or concern about saturating the receiver?

Rob, the Colpitts circuit is not convenient to work with a strong TX current because it requires two large capacitances connected to TX coil. For example, if tank capacity is 1uF (reccomended), for feedback in emitter you need capacitance 4uF. To avoid this, you should use oscillator circuit with two transistors as in White's Classic.
Moreover, at a frequency of 15KHz is obtained too strong GND signal if the ground is wet (conductive). Easier to adjust the elimination of GND signal if the TX frequency is lower, for example 7KHz.
For maximal sensitivity, the inductance of RX coil should be maximal and limited by stray capacitance. However for stability should be conneced a capacitor, for example 1nF.
Mike-BG

[Qiaozhi]

Does anyone know any "standard" used for building the Double D coil for a IB detector? Let's assume about a 10" coil. I'll be using 24awg enameled wire for construction. What I'm looking for is what inductance and resistance is typically found on Double D coils on both the TX and RX on coils roughly this size. My best guess from what I've read is about 1mH TX and about 400uH RX??? I'm building my colpits oscillator and am targeting 15KHz but it is hard to figure out what the capacitance values are if you don't know the inductance.
Another question I would have is does anyone know roughly what the current levels are used in these coils? Is it just limited by battery life or concern about saturating the receiver?

Thanks!
Rob

Tesoro detectors (such as the Golden Sabre) use a Colpitts oscillator with approximate coil inductances of TX=6mH and RX=6.5mH.

[mikebg]

Another question I would have is does anyone know roughly what the current levels are used in these coils? Is it just limited by battery life or concern about saturating the receiver?

The efficiency of TX coil (Ampere-turns divided to battery power drain) increases with TX supply voltage and tank capacitance. This is valid also when the TX coil is powered in a given tap which increases efficiency additionally.
A center tap works excellent and if the TX end stage is driven (not self-oscillating) as in White's models: Coinmaster, TM808 and Eagle Spectrum. For White's coils the TX tank capacitance is 1uF and for f=6500Hz the total inductance is about 540uH @ r=1.4ohm.
If the RF amplifier saturates because the AIR and GND signals are large, then you should decrease the gain.
Mike-BG