Farzad E.

I'm trying to use an MSO5 series scope to do some low level measurements and I noticed persistent spurs at integer fractions of the sampling frequency, with significant spurs at 195.3125 MHz, 390.625 MHz and 781.25 MHz.

The level of the measured noise changes with the vertical settings and increases with larger vertical divisions.

I can even pick up a very faint (about -95dBm) 390.625MHz tone when the scope is running with a spectrum analyzer which sits next to it. The tone disappears when the scope is turned off.

Is this normal? I am new to Tektronix scopes.