Is this IGSL oscillator correct?

[MartyJ1963]

Hi all,,,,,I've been struggling to learn how to null 'DD' and 'CC' coils these past couple of months and I saw a post by Hyena (Tomas) saying that a lot of Inductance meters weren't to be trusted when solely relying on their readings in regards to tuning a certan Inductance to a specific frequency. I have several different Inductance meters and they all give totally different inductances when measuring the same coil so I understand what he's saying!,,Anyway,,Tomas suggests to build an Oscillator to connect the coil to, to find the frequency of the coil under test, and then calculate the inductance from that etc,,,,I have drawn the IGSL Musk oscillator in order to try this method as it is the IGSL Musk coil I'm struggling to null,,,As I've still got a lot to learn about electronics I'm wondering if some kind person would check my drawing for me to see if I have drawn it correctly,,,and also what power would apply to the circuit? I would be immensely grateful. Thanks,,,Marty

[chemelec]

Not sure why your getting different readings from your meters, or What Meters your Using?
Just a fixed frequency Oscillator is not very good.
It would be better if you were to use a Calibrated Signal Generator and a Oscilloscope to determine a peak waveform at resonance.

Especially at Higher Frequencies, you also need to take into account Any Parallel Capacitance to the Coil.
This Includes Capacitance in your Wires.

[MartyJ1963]

Hiya Chemelec,,,,I hope you enjoyed your holidays!,,,and I'm really sorry to hear about your health,,I really do hope things start getting better for you and send you my best wishes. Thanks for the reply to my post. More than anything, I really wanted to know if I had drawn the Oscillator correctly, and what power I had to apply to it for it to operate. I have 3 different inductance meters and they all give different inductance readings for the same coil. I have a Hantek DSO 5102P scope but I'm still learning to use it as I only bought it last August. The coil I'm trying to tune is a 'DD' for the IGSL Musk version. The TX=1MH and the RX=14.7MH. One of my meters says the coils measure near enough correctly (within a few UH) but the other 2 meters says I'm miles out!,,lol. I'd like to build this oscillator to try a known capacitor with it to measure the inductance and see what that tells me. Thanks again. Marty

[dbanner]

Hey, balancing/ nulling/ tuning coils is not good for one's own health. It is most difficult part of making metal detector project. Get clean bill of health first from good medical practitioner before attempting.
Now the final coil inductance is not so important so long as it is within say 2℅ of what is required. A few tens of uH up or down is of little consequence.
What is important is required Resonant frequency of the TX( the transmit signal I assume is sinus for tgsl/Igsl)
Connect the tx coil to your transmitter and measure the frequency of the waveform generated. You can do this using a frequency meter or a software program on computer via soundcard.
Just adjust capacitance up or down to get correct frequency bang on. Simple enough.

[dbanner]

So long as the intended inductance is in the ballpark, fasten the coil down to something with some tie straps. Make little board for various values of adding/ subtracting capacitance in 1 nF steps.
Have little 500picofarad variable trim capacitor connected for fine tuning.
After circuit oscillating at correct frequency then measure/ calculate amount of capacitance and replace with fixed permanent cap. Closest to required.
The frequency spread between the tx and Rx resonance is critical for circuit to work properly.
So if tx is say 100hertz above what is required, then adjust Rx resonance frequency to 100herrz more in order to maintain the spread. Get it?

[MartyJ1963]

@Dbanner,,,,,Thanks again for all the info,,,,Regards, Marty

[MartyJ1963]

Hi all,,,,Can anyone tell me if the IGSL Oscillator I drew is correct please and what voltage I need to apply to it to test a coil on?,,,Thanks in advance,,,Marty

[Hyena]

Musk oscilator

I think now its corrected... next time please always attach schematics.

[Hyena]

Its feeded with stabilised 8V in circuit - through 7808, but you can power it even directly from 9V battery.

[Davor]

Original oscillator is supplied with stabilised voltage, so all the biases are fixed against it. The only two problems with voltage stabilisers are their ridiculously high noise, and their voltage margin. Both problems should disappear with a slight design change that makes bias independent from rail voltage. When AB->C mod is applied, the bias turns off anyway, and battery supply becomes the ultimate power source. No 1/f noise whatsoever.