TGSL poor sensitivity/deepnes

[Psyborg]

Hi guys, i finaly finished my tgsl v.3, homemade pcb.
But something is not good. I have very poor sensitivity. Metal screwdriver at only 4cm from coils,
so i have been checking out every part and TestPoint with my osciloscope. My osciloscope is analog Hitachi dual channel 15Mhz.
First general data about coils:
Tx coil 6.0 mH, 12.4Ohm, 16,6kHz calculated with osciloscope.
Rx coil 6.6 mH, 13.3Ohm, 14.7nF, also 16,6kHz calculated with osciloscope.
I use usb2 cable.

Can somebody give me some advice how to gain a better sensitivity/deepnes?

[Koala]

Hi guys, i finaly finished my tgsl v.3, homemade pcb.
But something is not good. I have very poor sensitivity. Metal screwdriver at only 4cm from coils,
so i have been checking out every part and TestPoint with my osciloscope. My osciloscope is analog Hitachi dual channel 15Mhz.
First general data about coils:
Tx coil 6.0 mH, 12.4Ohm, 16,6kHz calculated with osciloscope.
Rx coil 6.6 mH, 13.3Ohm, 14.7nF, also 16,6kHz calculated with osciloscope.
I use usb2 cable.

Can somebody give me some advice how to gain a better sensitivity/deepnes?

what's the null on the coil

[Psyborg]

Channel A tx coil - 5V/div, 20uS/div AC setup
Channel B rx coil not connected to board 0.2V/div AC setup

[Koala]

[ATTACH]45780[/ATTACH]

Channel A tx coil - 5V/div, 20uS/div AC setup
Channel B rx coil not connected to board 0.2V/div AC setup

I make that 400 millivolts on the RX pre the opamp

normally null is measured while connected on pin 7 of U101a

[dbanner]

TX 14.9khz
Rx 16.1khz
These are the resonant frequency of tgsl coils.

[dbanner]

Using oscilloscope to guesstimate frequency is not adequate for this task.
6.6mH with 14.7nF cap gives resonant frequency of 16.15khz.
There is formula for calculating the resonant frequency or you can use Android apk. Resonant calculator app.
Tx should be oscillating at 14.9khz.(colpitts oscillator 20nf(C1*C2/C1+C2)
Rx coil is tuned to 16.1 kHz.
Play with Rx coil for reject ferrite with trimmer while having best sensitivity to coins and silver.
Play with it delicately like romantic lover, while monitoring scope, you can see a little before deep null, gives best performance.

[dbanner]

Finally, buy cheap Chinese coil, and repurpose for tgsl.
Chinese lover is best for this task. Cheaper harder quicker faster.
Coil making and balancing is most difficult task for the beginner, Nevermind shielding, which is a task within itself.
Best to look for cheap coil compatible for tgsl. Spend 40 bucks.

[Psyborg]

Thanks to answers, i will give my best to make tgsl to the end.

[Psyborg]

Using oscilloscope to guesstimate frequency is not adequate for this task.
6.6mH with 14.7nF cap gives resonant frequency of 16.15khz.
There is formula for calculating the resonant frequency or you can use Android apk. Resonant calculator app.
Tx should be oscillating at 14.9khz.(colpitts oscillator 20nf(C1*C2/C1+C2)
Rx coil is tuned to 16.1 kHz.
Play with Rx coil for reject ferrite with trimmer while having best sensitivity to coins and silver.
Play with it delicately like romantic lover, while monitoring scope, you can see a little before deep null, gives best performance.

So , if tx coil need to oscillate 14.9kHz with 20nF (C1 and C2) then coil must have 5.7mH. Is that correct??
In pdf 101 write under 1." The basic Colpitts oscillator. Together with the transmit coil attached to J1, it provides a
14.5 kHz low power Tx signal to the coil, audio circuit, -5v converter and a signal to use as a
phase comparison for the receive circuit. Tx amplitude should be in the 16V range."
If is 14.9kHz then 6mH is ok.

[kt315]

open link. https://www.tesoro.com/info/manuals/...bremanual.html
you have to see your deeply mistake. operating frequency is 12kHz, NOT 14.5.

[dbanner]

I made mistake, 14.5khz for TX is correct and 16.1khz for Rx as in document. Make it so.
If using 12khz for TX, then Rx set at 13.6khz. See? Same spread between tx and Rx maintain proper "off resonance". Circuit will perform just the same.

[Ozoz_xba]

Hi guys, i finaly finished my tgsl v.3, homemade pcb.
But something is not good. I have very poor sensitivity. Metal screwdriver at only 4cm from coils,
so i have been checking out every part and TestPoint with my osciloscope. My osciloscope is analog Hitachi dual channel 15Mhz.
First general data about coils:
Tx coil 6.0 mH, 12.4Ohm, 16,6kHz calculated with osciloscope.
Rx coil 6.6 mH, 13.3Ohm, 14.7nF, also 16,6kHz calculated with osciloscope.
I use usb2 cable.

Can somebody give me some advice how to gain a better sensitivity/deepnes?

Show me your coils and the nulling.if nulling is not done correct then your deepnes is weak or none.i have no skope but with an voltmetre can calculate the frequency and doing the nulling good at concentric coils which take 1 euro at 28 cm in air...