schematics
Hope, last posting twice is not my mistake!
Ok, I am trying to reduce the complexity but you are right without seeing it is hard to give an idea 8)
Here is what I tried;
1- first I try this microchip app-note deisgn;
https://www.electro-tech-online.com/custompdfs/2005/09/00236a.pdf
please see pic1
using ordinary NOT gates as an amplifier is a good idea, but the gain is not enough when I try a 100m cable. With little modifications it worked with 1- 30meters, freq is 120kHz.
2- Then I tried standart op-amp amplifier circuits a few just to see and get familiar with the op-amps, and especially concentrated on one circuit, please look at
**broken link removed**
**broken link removed**
I understand this circuit pretty well, the problem is this is designed for audio which is far beyond my PCM freq 120kHz. If this circuit can work for 120kHz I think I will be able to tune its AGC. As far as I can see LM358 is not suitable for such a gain.
So I tried to use the two stages of LM358, make the first stage an amplifier only and feed the second stage with this to amplifie again and use the AGC circuit. But could not sucessfull. The signal is not amplified enough in neither of the circuits. And there is noise at the output, even when I cut its relation with the coupler. I tried to decouple of the power supply, the noise attenuated a little but not dissaperaed.
3- I searched web for amplifier ICs, like MC1350 but its price is rather much for such a circuit, so did not tested yet.
Maybe I am missing some key points to ask, so I ask you "how do you amplifie a 120kHz signal", I try to write some details in my first posting such as voltage levels, but maybe these are not enough also?
Thanks,