TESORO GOLDEN SABRE

[Carl-NC]

The fact that the problem never goes away no matter where the RX coil is placed suggests that the main problem might be a bad null. Another possibility is that there is too much preamp gain.

[pito]

not very well nulled. = flats on top and bottom, he got it only on one side

[Carl-NC]

Thanks, another question, what could be the reason of not having a perfect sine shape in the RX preamp output? My RX waves have always some flat bottom.

You either have too much offset in the preamp or the coil is not very well nulled.

[pito]

some flat bottom. = incorrect bias

[cristiano.sar]

Thanks, another question, what could be the reason of not having a perfect sine shape in the RX preamp output? My RX waves have always some flat bottom.

[pito]

In VLF direction finders the shield is used to have sharp null , the same is in metal detectors.....

[cristiano.sar]

I'm experimenting coil nulling with my TGSL.
My coil is shielded with graphite (about 1.2k resistance) and connected to the board via usb 2.0 cable, using the shield connected to pin TX-2.
While observing the waveforms in oscilloscope I noticed that when I have the shield disconnected and move the RX the coil around I have more room to find the desired phase shift while with the shield connected it seems more difficult if not impossible to get it.
Is this a normal behaviour?

Shield disconnected: https://youtube.com/shorts/tSZ8m-IoOu4
Shield connected: https://youtube.com/shorts/KqA1BemDo3s

[cristiano.sar]

I'm having a similar problem.
Positive voltage: +7.97v, negative voltage: -6.37v.
My TGSL TX amplitude is around 10v, checked the resistance of J1-1 to ground with the TX coil disconnected and it measures about 0.7 Meg, should I worry about?
Thanks.

Well, I just found that the problem is my scope, the button at 5v/Div does not work very well, just moving it some millimeter clockwise or using the 2v/Div I can get around 14 and 15v of TX amplitude.

[cristiano.sar]

Sorry, I meant the regulated V+ at the LM7808 output pin 3 (should be +8 Volts) and the negative supply rail (from Diode D6 and Capacitor C5, should be about -5 to -6.5 Volts).

Easiest place to check is the V+ and V- pins of the IC's, see the schematics. They should all (except CD4024) show +8 volts on the V+ pin and approx -5 to -6.5 volts on the V- pin.

If your V+ and V- "rails" are correct voltage, let's concentrate on your oscillator section (TR1, C1, C2, R1, R2, R3). Something seems wrong there. Make sure values of parts are correct and transistor working OK -- I guess you already did that somewhat.

It is also possible something is draining current from your oscillator, like a solder bridge between traces. Check the resistance from J1-1 (same as TR1 collector) to ground. It should be really high, mine measured over 2 Meg.

If you have any extra coil approx 6 mH, disconnect your TX/RX coils and just connect the extra coil directly to oscillator and measure voltage. If possible disconnect the cable also. This is just in case you have some wiring problem in your cable or TX/RX coils.

Regards,

-SB

I'm having a similar problem.
Positive voltage: +7.97v, negative voltage: -6.37v.
My TGSL TX amplitude is around 10v, checked the resistance of J1-1 to ground with the TX coil disconnected and it measures about 0.7 Meg, should I worry about?
Thanks.

[Justihnno]

Hello! Has anyone simulated the circuit in Orcad and can they please help me with it?

[mostafalesnar91]

https://m.youtube.com/watch?v=lVrwQNLVg98

[mostafalesnar91]

there is a way to balance by ferrite ring (offer by russian). take the ring and put in center of coil.
input in it a wire of TX coil and a wire of RX one. you must seek up optimal number of the turns and their direction.
i have his pic somewhere but can not find right now.

I followed qiazhi's advice, I balanced the coil to remove the ferrite!!!here is noise in this film in the home environment, otherwise the device works fine, I just can't remove the foil with the disc volume.

[kt315]

there is a way to balance by ferrite ring (offer by russian). take the ring and put in center of coil.
input in it a wire of TX coil and a wire of RX one. you must seek up optimal number of the turns and their direction.
i have his pic somewhere but can not find right now.

[mostafalesnar91]

expected... now a good time to throw out first coil and to make second.
i noticed you do not want to hear suggestions. your ears seems covered by wax.

The ferrite is rejected and disc mode works fine so I'm on the right way!!!

[kt315]

expected... now a good time to throw out first coil and to make second.
i noticed you do not want to hear suggestions. your ears seems covered by wax.