I have a circuit with an analogic part and with a digital part. The thing is that if i just turn on one of the voltage suppliers (doesnt matter wich one) i have a nice signal, but when i turn on the second voltage supplier i get a lot of noise even with the strobe in the air, not touching anything. I get a noise of 100mV peak-peak that adds to my signal.
I dont understand the question "what are the voltage suppliers?" you mean the brand?
They are not tied togheter as the digital part has its own ground, just like the analog. one is giving 5V(analog part) while the other is giving 3.3V(digital part)
Its ok, you've answered my question 5v and 3.3v. I was checking that there was no contention between the two voltages... All I can suggest is you make sure ALL IC's have 0.1uf decoupling caps.. I'm not so sure about the separate grounds though, I usually have a common ground that has a different path back to the supply.
I was just thinking... 50mhz... its kinda high for noise.. especially one that's affected by a linear power supply (noise on these are usually in the order of 50khz)
With so much lab equipment on the mains, you may need an isolation transformer... IF you source power temporarily from a battery (I'm assuming the source is from the mains at the moment) it would eliminate your circuit.
I'd guess this is a grounding problem. Try connecting both 'grounds' to a common point grounded with respect to the mains supply. Mounting your kit in a screening box also connected to that common point would probably help, too.