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Products => Test Equipment => Topic started by: ronsch on May 07, 2015, 05:05:10 pm

Title: Siglent 1102CML FFT Peaks
Post by: ronsch on May 07, 2015, 05:05:10 pm

I recently purchased a Siglent SDS 1102CML (100Mz) scope and was using it to look at some noise on a power supply.  I noticed two stable peaks in the FFT at 50Mz and 100Mz which remained even when I removed the probes..  I am relatively new to scopes and am wondering if it is typical to have FFT peaks on harmonics of the scope frequency.  I have attached a screenshot.  Any suggestions are welcome.

Ron

Title: Re: Siglent 1102CML FFT Peaks
Post by: tautech on May 07, 2015, 09:54:54 pm

Quote from: ronsch on May 07, 2015, 05:05:10 pm

I recently purchased a Siglent SDS 1102CML (100Mz) scope and was using it to look at some noise on a power supply.  I noticed two stable peaks in the FFT at 50Mz and 100Mz which remained even when I removed the probes..  I am relatively new to scopes and am wondering if it is typical to have FFT peaks on harmonics of the scope frequency.  I have attached a screenshot.  Any suggestions are welcome.

Ron

Welcome to the forum.

It is normal to see all sorts of garbage if the probes are not terminated to a DUT.
Internally the SDS1000 series have 3 clocks, 25, 30 and 100MHz. (check the Service manual)
Even the lowest BW model in the SDS1**2C*L has the same clocks.

BTW to check PSU noise/ripple one would normally use AC input coupling and mV/div amplitude setting, then adjust timebase and triggering to analyse the displayed waveform.