TESORO GOLDEN SABRE

[pito]

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

[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]

Proper bias/offset make sine symmetric, to high gain make amplitude limit.

@cristiano.sar

Go from this (right drawing )

to this


Then reduce gain and get this

[pito]

the problem never goes away = it is go away very easy with this phase shifter + potentiometer for amplitude regulation.


There is no need to waste time for perfect coil nulling, just make it less than 1V ........

[Carl-NC]

After looking at the video again, I think the null is OK, but something is wrong with the preamp. I would check the negative power supply, see if it is connected correctly and maintaining regulation. Or try a different opamp.

[pito]

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.

Positive voltage: +7.97v, negative voltage: -6.37v. = This is your problem; the voltages should be the same

[kt315]

but something is wrong with the preamp.

where he bought the opamp? is it chinese special for aviation and space usage?

[ArchibaldSTM]

pito...It's not a problem. TGSL has power supply +8 volts / -5 volts

[pito]

If you have unsymmetrical positive and negative voltages the limitation will be oslo unsymmetrical, for small signal where is no limitation sin will be without flats.

[ArchibaldSTM]

We are not interested in the lower half-wave --- only the upper half-wave is used for subsequent processing

[pito]

the question was in post #6223

[cristiano.sar]

Thanks for the help.
I changed the LM358 by 2 others of different brands and the result is more or less the same. Also tested the resistors and capacitors around the power supply and all is within the spec. Anyway the negative voltage is always around -6.4v . Now I'm waiting another LM358 just to do another test. I also noticed that moving the RX coil, in a certain position I have an almost perfect sine wave of the RX. I will try a little more and if I can't get good results I will make another board (purchased some from pcbway) because this one was my first and was home etched.

[pito]

Now I'm waiting another LM358 = wasting the time , it is not going to help.
I also noticed that moving the RX coil, in a certain position I have an almost perfect sine wave of the RX = because input signal is so small that after amplification it is below amplitude limitation.
The simplest solution is reducing amplifier gain by increasing capacitor across pins 6 and 7, 10pF it is wrong.

[Adam24]

I am working in Protel DXP,,he is very dificult ,,I recommend you eagle,,but find full version,,,,ask your friend is this board tested ,,does it work,,,I started to losing faith in people and projects on this forum,,i made a board for Coin hawk and he doesnt work,,then I made'd board for white 3900 and he also doesn't work,,I am investing lot of time and effort,,,in last time that was vain..

Hi there this is Adam from Egypt,so have you found a schematic with clear print detailed yet workable.thanks

[kt315]

Hi there this is Adam from Egypt,so have you found a schematic with clear print detailed yet workable.thanks

i still have a PCBs' batch on GMT KING COBRA (GMT GOLD SCORPION) and can send to you. 18 euro cost with sending.