Siglent SDG2042X 30MHz Sine Wave THD vs. Output Power

[graybeard]

I measured the sine wave THD (total harmonic distortion) of my new Siglent SDG2042X function generator last night using my Siglent SVA1015X spectrum analyzer.   The total harmonic distortion at 0dBm output into 50 Ohms at 30 MHz exceeds the published specification of -55 dBc by more than 10 dB.  This is excellent.  However the distortion rises with output power and increases to -45 dBc at 5Vpp (18dBm).



I used an external 20 dB attenuator in combination with the SVA1015X internal attenuator for the +10 dBm and +18 dBm measurements.

+18 dBm


+10 dBm


For the 0dBm and -20 dBm measurement I removed the external attenuator and used only the SVA1015X internal attenuator.

0 dBm


-20 dBm


For the -45 dBm measurement I turned on the SVA1015X internal preamplifier.  In this measurement you can see noise floor plus spurs of the of the output of the SDG2042X is at -95 to -100 dBm above 60MHz.

-45 dBm


If I were to use the SDG2042X as a low distortion RF source at 30 MHz I would stick to output powers between -20 dBm to 0 dBM and use an external attenuator, since the distortion increases above 0 dBm.

Overall my initial impression so far of the SDG2042X is this is excellent performance, especially for the price.

Chris

[kg4arn]

Thanks. I just bought one a week ago but haven’t looked at the output spectrum yet.

[graybeard]

Thanks. I just bought one a week ago but haven’t looked at the output spectrum yet.

Mine arrived on Monday.  I bought it from Saelig since they offer an EEVblog member discount.