I've got strange noise while using digital oscilloscope (Auris B-424). Spectrogram of this signal presented on this image: (X time in seconds, Y frequency in Hertz, in this image case from 0 to 50 MHz) Zoomed versions: 1, 2 On oscillogram noise looks like impulse interference with amplitude approximately 10 millivolts.
Simple scheme (fiber semiconductor detector) is connected to the input of oscilloscope with short 50 Om coaxial cable. Without anything on input channel noise is significantly lower (10-15 times), although still presented. Surge protector and ground used for powering oscilloscope and notebook. (outer conductor of coaxial cable is grounded too) My main guess is impulse interference from notebook and oscilloscope itself, but I can't find way to deal with it.
What do you think? What nature has this noise and is there any way to reduce it?